Dr. Jeff Masters' WunderBlog

Hurricane Irene: New York City dodges a potential storm surge mega-disaster

By: JeffMasters, 04:14 PM GMT del 30 novembre 2011

On August 24, 2011, I had good reason to fear New York City's worst-case storm surge disaster might be named Irene. As Category 3 Hurricane Irene ripped through the Bahamas on its way to North Carolina and New England, our most reliable hurricane forecasting model--the European (ECMWF) model--predicted that Irene would intensify to Category 4 strength with a 912 mb central pressure as it grazed the Outer Banks of North Carolina, then slowly weaken to a Category 3 hurricane before hitting southern New Jersey. Just a small perturbation from this scenario would bring Irene over New York City as a Category 2 hurricane. Since Irene was an exceptionally large storm with winds that covered a huge stretch of ocean, the storm had a much larger storm surge than it peak winds would suggest, and could have easily brought a storm surge of 15 - 20 feet to New York City. The storm would arrive during the new moon, when tides were at their highest levels of the month, compounding the storm surge risk.

Thankfully, the ECMWF model was wrong, and Irene's eyewall collapsed before the hurricane reached North Carolina. Irene made a direct hit on New York City as a tropical storm with 65 mph winds. Irene's storm surge reached 4.3 feet at the Battery on the south shore of Manhattan, which was high enough to top the city's seawall and flood low-lying park lands and roads near the shore. Fortunately, the water was not high enough to flood New York City's subway system, which could have easily occurred had Irene's winds been just 5 - 10 mph stronger.


Figure 1. Wind forecast for August 28, 2011 made on August 24, 2011 by the ECMWF model for Hurricane Irene. The model predicted that Irene would be a Category 3 or 4 hurricane with a 936 mb central pressure four days later, just south of New Jersey.

New York City: my number one storm surge disaster concern
I met last year with the head of the National hurricane Center's storm surge unit, Jaime Rhome, and asked him what his number one concern was for a future storm surge disaster. Without hesitation, he replied, "New York City." I agreed with him. Strong hurricanes don't make it to New York City very often, since storms must hit the city from the south or southeast in order to stay over water, and most hurricanes are moving northeast or north-northeast when they strike New England. New York also lies far to the north, where cold water and wind shear can tear up any hurricane that might approach. But if you throw the weather dice enough times, your number will eventually come up. New York City's number came up on September 3, 1821, when what was probably a Category 2 hurricane with 110 mph winds struck the city. The water rose 13 feet in just one hour at the Battery, and flooded lower Manhattan as far north as Canal Street--an area that now houses the nation's financial center. The maximum storm surge from this greatest New York City hurricane is unknown, but could have been 15 - 20 feet, which is what NOAA's SLOSH model predicts could occur for a mid-strength Category 2 hurricane with 100-mph winds.


Figure 2. The height above ground that a mid-strength Category 2 hurricane with 100 mph winds would would create in New York City in a worst-case scenario. The image was generated using the primary computer model used by the National Hurricane Center (NHC) to forecast storm surge--the Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model. The accuracy of the SLOSH model is advertised as plus or minus 20%. This "Maximum Water Depth" image shows the water depth at each grid cell of the SLOSH domain. Thus, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. This Maximum of the "Maximum Envelope of Waters" (MOM) image was generated for high tide and is a composite of the maximum storm surge found for dozens of individual runs of different Category 2 storms with different tracks. Thus, no single storm will be able to cause the level of flooding depicted in this SLOSH storm surge image. Consult our Storm Surge Inundation Maps for the U.S. coast for more imagery.

New York City's storm surge history
During the December 12, 1992 Nor'easter, powerful winds from the 990 mb storm drove an 8.5-foot storm surge into the Battery Park on the south end of Manhattan. The ocean poured over the city's seawall for several hours, flooding the NYC subway, knocking out power to the entire system. One train had to be backed out of a tunnel that was filling with water, and hundreds of passengers were rescued from stranded trains. Portions of the Port Authority Trans-Hudson Corporation (PATH) train systems in New Jersey were shut down for ten days, after low points in the rail tunnels flooded and major damage occurred to the control signals. Passengers had to be rescued from a train stalled in the PATH tunnel. Surges only one to two feet higher may have caused massive flooding of the PATH train tunnels. La Guardia Airport was closed due to flooded runways. Roadway flooding was also widespread—FDR Drive in lower Manhattan flooded with 4 feet of water, which stranded more than 50 cars and required scuba divers to rescue some of the drivers. Battery Park Tunnel held six feet of water. Major parkways were flooded in Nassau County, Westchester County, and New Jersey. Mass transit between New Jersey and New York was down for ten days, and the storm did hundreds of millions in damage to the city. The situation was similar in September 1960 during Hurricane Donna, which brought a storm surge of 8.36 feet to the Battery, and flooded lower Manhattan to West and Cortland Streets. The November 25, 1950 Nor'easter brought sustained easterly winds of up to 62 mph to LaGuardia Airport, and pushed a large storm surge up Long Island Sound that breached the dikes guarding the airport, flooding the runways.


Figure 3. Water pours into the Hoboken, New Jersey underground PATH mass transit station during the December 12, 1992 Nor'easter. Image credit: Metro New York Hurricane Transport Study, 1995.


Figure 4. Flooded runways at New York's La Guardia Airport after the November 25, 1950 Nor'easter breached the dikes guarding the airport. Sustained easterly winds of up to 62 mph hit the airport, pushing a large storm surge up Long Island Sound. The storm's central pressure bottomed out at 978 mb. Image credit: Queens Borough Public Library, Long Island Division.

Sea level rise and New York City
According to tide gauge data, sea level at the Battery at the south end of Manhattan has risen about 1 foot since 1900. This is higher than the mean global sea level rise of 7 inches (18 cm) that occurred in the 20th century. Global sea level rise occurs because the oceans are expanding as they heat up, and due to melt water from glaciers. The higher sea level rise in New York is due to the fact the land is sinking along the coast. These processes will continue during the coming century.

The U.N.'s Intergovernmental Panel on Climate Change (IPCC), predicted in 2007 a 0.6 - 1.9 foot global average sea level rise by 2100. However, they did not include melting from Greenland and Antarctica in this estimate, due to the large uncertainties involved. A paper published by Pfeffer et al. (2008) in Science concluded that the "most likely" range of sea level rise by 2100 is 2.6 - 6.6 feet. Three major sea level papers published since the IPCC report was issued in 2007 all agree that the IPCC significantly underestimated the potential sea level rise by 2100. In a 2009 interview with New Scientist magazine, sea level expert/ glaciologist Robert Bindschadler of the NASA Goddard Space Flight Center in Greenbelt, Maryland, commented, "most of my community is comfortable expecting at least a meter (3.28') by the end of this century." Sea level expert Stephan Rahmstorf added, "I sense that now a majority of sea level experts would agree with me that the IPCC projections are much too low." However, he cautioned that the popular media tend to focus on the upper limits of these newer projections (1. 5 - 2.0 meters), and "reaching the upper limits is, by definition, extremely unlikely.""

The sea level rise situation will be worse in areas where ocean currents have a large impact on the local sea level. This is the case along the Northeast U.S. coast, where the balance of forces required to maintain the very strong and narrow Gulf Stream Current means that sea water is sucked away from the coast, lowering the relative sea level from North Carolina northwards. During the coming century, the addition of large amounts of heat and fresh water into the North Atlantic due to higher precipitation, river runoff, and increased melting of glaciers is expected to weaken the Meridional Overturning Circulation (MOC) (also referred to as the thermohaline circulation), a global network of density-driven ocean currents. Weakening the thermohaline circulation will allow the Gulf Stream to spread out, resulting in sea level rise along the Northeast U.S. coast. Hu et al. (2009) found that a slow-down of the Meridional Overturning Circulation by 48% may occur by 2100, resulting in a 0.1 - 0.3 meter (0.25 - 1.0 ft) rise in sea level along the U.S. Northeast coast and Canadian Atlantic coast. This rise would be in addition to global sea level rise from melting glaciers and thermal expansion of the waters. A similar study by Yin et al. (2009) found a slow-down of the Meridional Overturning Circulation of 41% by 2100. New York City was in the region with the highest expected sea level rise from this ocean current effect--a rise of about 0.2 meters (0.75 feet) by the year 2100. If the Atlantic thermohaline circulation were to totally collapse, the authors predict a 4 ft (1.2 meter) rise in sea level along the U.S. Northeast coast solely due to the change in ocean currents. The IPCC predicts that such an abrupt climate change event (rather ridiculously depicted in the movie The Day After Tomorrow) will not occur in the coming century, though.

The future: Stronger hurricanes for New York City?
According to a summary statement endorsed by 125 of the world's top hurricane scientists at the World Meteorological Organization (WMO) Sixth International Workshop on Tropical Cyclones, in San Jose Costa Rica, in November 2006. "it is likely that some increase in tropical cyclone intensity will occur if the climate continues to warm." This makes intuitive sense, since hurricanes are heat engines that convert the heat of the ocean waters into the mechanical energy of wind. Turn up the thermostat, and you increase the energy available to make the strongest storms stronger. One major reason hurricanes weaken quickly when they approach New England is that the coastal waters cool dramatically north of North Carolina. As ocean waters warm during the coming century, hurricanes will be more able to maintain their strength farther to the north. One of the reasons the ECMWF model was simulating a 936 mb Hurricane Irene hitting New Jersey was because ocean temperatures off the mid-Atlantic coast were 1°C (1.8°F) above average during August 2011--the 7th warmest in recorded history. These high ocean temperature were due to the exceptional heat wave that gripped much of the mid-Atlantic during the summer of 2011--every state along the coast from Florida to New Jersey had a summer that ranked in the top four warmest summers since 1895. Such heat waves and warm ocean temperature are expected to become the new normal by mid-century, resulting in increased chances for strong hurricanes to make it to New England.


Figure 5. Summer temperatures along the U.S. Atlantic coast during 2011 ranked as 2nd - 4th warmest on record from Florida to New Jersey, resulting in exceptionally warm waters along the coast for Hurricane Irene to feed off of in late August. Image credit: National Climatic Data Center.

The other major reason that strong hurricanes have trouble making it to New England is that wind shear generally increases as one gets closer to the pole, due to the presence of the powerful winds of the polar jet stream. However, climate change theory predicts that the jet stream should migrate poleward during the coming decades, potentially reducing the amount of wind shear hurricanes arriving in New England will experience. A 2008 study by Archer and Caldeira found that the jet stream moved northwards 125 miles per decade during the 22-year period 1979 - 2001, in agreement with climate change theory. However, the migration of the jet stream northwards may also mean that hurricanes will be less likely to be caught up in a trough of low pressure embedded in the jet stream, resulting in fewer hurricanes swinging northwards to impact New England. At this point, it is hard to say whether or not changes to the jet stream due to climate change will alter the frequency of strong hurricanes reaching New England.

New York City's inadequate sea wall
The floodwalls protecting Manhattan are only five feet above mean sea level. At high tide, the water is only 3.5 feet below the top of the seawall, so clearly Manhattan is going to have a serious storm surge problem by the end of the century if sea level rise reaches the 3-foot plus figure many sea level rise scientists are predicting. As Ben Straus of Climate Central pointed out in a blog post on Irene, "sea level rise will amplify the impact of future hurricanes and Nor'easters. If we replay the 20th century but add an extra foot of sea level at the start (the extra foot we indeed started with in 2000, compared to 1900), about six events would produce higher water levels than the Nor'easter of 1992." Remember, the 1992 Nor'easter crippled the city's transportation system for ten days and caused hundreds of millions in damage. A Category 2 hurricane like the 1821 hurricane would be far worse, and could result in severe global economic consequences. A 15-foot storm surge from such a hurricane would swamp JFK and La Guardia airports. Manhattan would flood north to Canal Street, shutting down Wall Street and New York City's Financial District. The Holland Tunnel, much of the NYC subway system, and the New Jersey PATH mass transit systems would all flood. Many of the power plants that supply the city with electricity might be knocked out, or their docks to supply them with fuel could be destroyed. Nearly half a million people and almost 300,000 jobs lie within the Federal Emergency Management Agency (FEMA) 0.2-percent-annual-chance flood zones that would be inundated. As New York Times columnist Nate Silver wrote, such a disaster would likely cost near $100 billion. Furthermore, he makes the point, "Keep in mind that New York City's annual gross domestic product is about $1.4 trillion, one-tenth of the nation's gross domestic product, so if much of the city were to become dysfunctional for months or more, the damage to the global and domestic economies would be almost incalculable."


Figure 6. The seawall protecting Manhattan at Battery Park is only 5 feet above mean sea level. Tidal range at the Battery is plus or minus 1.5 feet, so at high tide a storm surge of just 3.5 feet is needed to send water over the seawall and into Manhattan.

Flooding of the NYC subway system
The U.S. Federal Transit Administration released a report in October 2011 called, "Flooded Bus Barns and Buckled Rails: Public Transportation and Climate Change Adaptation". The report says that with three feet of sea-level rise, the flooding produced by a 100-year storm at current sea levels will require only a 10-year storm, in other words, a tenfold increase in the frequency of flooding. Even without sea-level rise, a 100-year flood (an 8-foot storm surge) would inundate substantial portions of the subway system, whose tunnels generally lie twenty feet below street level. With sea-level rise though, the flooding occurs more rapidly and is more severe. A 100-year flood with a four foot rise in sea level would flood a large fraction of Manhattan subways, including virtually all of the tunnels crossing into the Bronx beneath the Harlem River and the tunnels under the East River. Flood waters enter the subway tunnels mostly vertically via ventila­tion grates and entrances as the streets flood, but also via inclined rail and road tunnels. Hydraulic computations show complete flooding takes only 40 minutes. Recovery would require obtaining huge quantities of pumps and hoses, awaiting restoration of power to the electrical grid, pumping out the flood waters, cleaning out miles of muddy and debris-filled platforms, stairs, tunnels and trackway, assessing the damage, and repairing problems. Much of the signal equipment and controls in the tunnels would be damged by salt or brackish water and would need to be disassembled, cleaned, and repaired or replaced to avoid corrosion and irreparable long-term damage. This specialized equipment, some of it 100 years old, is difficult to obtain and in many cases no longer manufactured. Researchers estimate a minimum recovery time of three to four weeks to reach 90 percent capacity, although when engineers were presented with the question, they believed that it could take one to two years to recover fully. This also assumes trains were moved to portions of the system with elevations above flood levels, in anticipation of the storm and were thus not damaged. Additional problems could result if the flood waters were contami­nated with toxins. Combined economic and physical damage losses from subway tunnel flooding under a 100-year storm surge were estimated at $58 billion at current sea levels and $84 billion with four feet of sea-level rise, assuming a linear recovery and an estimated subway outage time of three to four weeks.


Figure 7. New York City Subway vulnerability to a 100-year flood of 8 feet, with a 4-foot sea level rise. Blue lines are flooded subway tunnels. Orange areas have elevation less than 30 feet at present. Subway tracks are typically 20 feet below street level. Image credit: New York State Energy Research and Development Authority (NYSERDA), ClimAID: Responding to Climate Change in New York State, Draft Version, 2010.

What to do? Build a storm surge barrier
As I discussed in Part One of this series on U.S. storm surge risk, three cities in New England--Stamford, Providence, and New Bedford--have already built hurricane storm surge barriers that have more than paid for the cost of their construction in damages saved. Many coastal cities will need to substantially improve their flood defenses in coming decades due to rising sea levels. For New York, the best solution is to place three barriers at strategic "choke points"—the Verrazano Narrows, Throgs Neck, and the Arthur Kill, argues Douglas Hill of Stony Brook University's Storm Surge Research Group. I'll present his arguments in a guest post in Part Three of this series on storm surge risk in the U.S., coming up sometime in the next week.

Resources and references
Storm surge barriers: the New England experience: Part One of this series on U.S. storm surge risk.

The National Hurricane Center's Interactive Storm Surge Risk Map, which allows one to pick a particular Category hurricane and zoom in to see the height above ground level a worst-case storm surge may go.

Wunderground's Storm Surge Inundation Maps for the U.S. coast.

Climate Change Adaptation in New York City: Building a Risk Management Response: New York City Panel on Climate Change 2010 Report

Climate change information resources for NYC from Columbia University.

Landstrike is an entertaining fictional account of a Category 4 hurricane hitting New York City.

Colle, B.A., et al., 2008, New York City's vulnerability to coastal flooding: storm surge modeling of past cyclones, Bull. Am. Meteor. Soc. 89, 829–841 (2008).

Hu, A., G. A. Meehl, W. Han, and J. Yin (2009), "Transient response of the MOC and climate to potential melting of the Greenland Ice Sheet in the 21st century", Geophys. Res. Lett., 36, L10707, doi:10.1029/2009GL037998 29 May 2009

Rignot, E., and P. Kanagaratnam (2006), Changes in the velocity structure of the Greenland Ice Sheet, Science, 311, 986. 990.

Yin, J., M.E. Schlesinger, and R.J. Stouffer, 2009, "Model projections of rapid sea-level rise on the northeast coast of the United States", Nature Geoscience 2, 262 - 266 (2009).

Lady Liberty not at risk from a storm surge
As a side note, the Statue of Liberty is not vulnerable to a storm surge, since the good lady stands atop a 65-foot high foundation and 89-foot high granite pedestal. However, the 305' height of the lady's torch above the foundation means the statue will experience winds a full Saffir-Simpson category higher than winds at the surface. The statue is rated to survive a wind load of 58 psf, which is roughly equivalent to 120 mph winds (Category 3 hurricane). However, a mid-strength Category 2 hurricane with 105 mph winds will be able to generate 120 mph winds at a height of 300 feet, and would theoretically be capable of toppling the Statue of Liberty.

Jeff Masters

Hurricane Sea level rise Climate Change

Updated: 03:00 PM GMT del 02 Dicembre 2011

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The 2011 Atlantic hurricane season: another strangely active one

By: JeffMasters, 04:08 PM GMT del 28 novembre 2011

Wednesday marks the final day of the 2011 Atlantic hurricane season, and it was another very odd year. The season featured a huge number of named storms--nineteen--tying 2011 with 2010, 1995, and 1887 as the 3rd busiest year for tropical storms. Only 2005 and 1933 had more named storms since record keeping began in 1851. However, 2011 had an unusually low percentage of its named storms reach hurricane strength. The year started out with eight consecutive tropical storms that failed to reach hurricane strength--the first time on record the Atlantic has seen that many storms in row not reach hurricane strength. We had a near-average average number of hurricanes in 2011--seven--meaning that only 37% of this year's named storms made it to hurricane strength. Normally, 55 - 60% of all named storms intensify to hurricane strength in the Atlantic. There were three major hurricanes in 2011, which is one above average, and the total Accumulated Cyclone Energy (ACE)--a measure of the destructive potential of this season's storms--was about 20% above average. The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is no doubt at least partially responsible for 2011's unusually high count of named storms, but near-average number of hurricanes and ACE. Both 2010 and 2011 had nineteen named storms, making it the second busiest 2-year period in the Atlantic behind 2004 - 2005. Even when one considers that 2 - 4 tropical storms from both 2010 and 2011 would likely have been missed before the advent of satellites, the tropical storm activity of 2010 - 2011 is still very remarkable (in 2011, Tropical Storm Franklin, Tropical Storm Jose, and the unnamed 19th tropical storm of September 1 would probably have been missed before satellite technology came along, since they were all weak, short-lived storms that did not impact land or shipping.)


FIgure 1. Tracks for the Atlantic tropical cyclones of 2011.

Another below-average hurricane season for the U.S.
For the second consecutive year, despite a near-record number of named storms in the Atlantic, the U.S. had far fewer strikes by tropical storms and hurricanes than average. Favorable steering currents steered most of the storms in 2010 and 2011 past Bermuda and out to sea. During 2010, only one tropical storm hit the U.S., despite a season with the 3rd highest number of named storms--nineteen. Only two named storms hit the U.S. in 2011: Tropical Storm Lee, which hit Louisiana with 60 mph winds, and Hurricane Irene, which hit North Carolina on August 27 with 85 mph winds, and made two additional landfalls in New Jersey and New York the next day. Tropical Storm Don hit Texas on July 29 as a tropical depression and did not count as a landfalling named storm, according to post analysis by NHC. Wind shear and dry air from the Texas drought made Don rapidly weaken before landfall on Padre Island National Seashore north of Brownsville. During the 15-year active hurricane period from 1995 - 2009, 33% of all named storms in the Atlantic hit the U.S., and 30% of all Atlantic hurricanes hit the U.S. at hurricane strength. The U.S. averaged seeing six named storms per year, with four of them being hurricanes and two being intense hurricanes. Thus, the landfall of only three named storms in a two-year period is a major departure from what happened the previous fifteen years. The past six years is the first six-year period without a major hurricane strike on the U.S. since 1861 - 1868. The last major hurricane to hit the U.S. was Category 3 Hurricane Wilma of October 2005. One caveat to keep in mind, though: Hurricane Ike and Hurricane Gustav of 2008 both hit the U.S. as strong Category 2 hurricanes, and had central pressures characteristic of Category 3 hurricanes. Had these storms occurred more than 65 years ago, before the Hurricane Hunters, Ike and Gustav would likely have been classified as Category 3 hurricanes at landfall (assuming that few quality wind observations would have been available at landfall, which is usually the case.)


Figure 2. The scene in Nassau in the Bahamas at daybreak on August 25, 2011 during Hurricane Irene. Image credit: Wunderblogger Mike Theiss.


Figure 3. The eye of Hurricane Irene as seen by hurricane hunter and wunderblogger LRandyB on August 24, 2011, when the hurricane was approaching the Bahama Islands.

The strongest, deadliest and longest-lived storms of 2011
The strongest hurricane of 2011 was Hurricane Ophelia, which peaked as a Category 4 hurricane with 140 mph winds and a central pressure of 940 mb on October 2, when it was just northeast of Bermuda. Ophelia hit Southeast Newfoundland as a tropical storm with 70 mph winds on October 3, but caused little damage. The strongest hurricane at landfall was Hurricane Irene, whose 120-mph eyewall winds raked Crooked Island, Long Island, Rum Cay, Cat Island, Eleuthera, and Abaco Island in the Bahamas. Wind gusts as high as 140 mph were reported in the Bahamas.The longest-lived storm of 2011 was Hurricane Phillipe, which lasted 15 days, from September 24 to October 8. The most damaging storm was Hurricane Irene, which caused an estimated $7.2 billion in damage from North Carolina to New England, according to re-insurance broker AON Benfield. Irene was also the deadliest storm of 2011, with 55 deaths in the Caribbean and U.S.



Figure 3. Pre-season Atlantic hurricane season forecasts issued by seven major forecast groups. The average of these forecasts called for 15 named storms, 8 hurricanes, 4 intense hurricanes, and an ACE index 150% of normal. The actual numbers were 19 named storms, 7 hurricanes, 3 intense hurricanes, and an ACE index 120% of normal.

Pre-season hurricane forecasts did a decent job
The pre-season Atlantic hurricane season forecasts issued by seven major forecast groups were generally decent. The average of these forecasts called for 15 named storms, 8 hurricanes, 4 intense hurricanes, and an ACE index 150% of normal. The actual numbers were 19 named storms, 7 hurricanes, 3 intense hurricanes, and an ACE index 120% of normal. Phil Klotzbach and Bill Gray of Colorado State will be releasing their end-of-season verification and summary of the 2011 Atlantic hurricane season on November 30.


Figure 4. Portlight volunteers at work in Pink Hill, North Carolina, after Hurricane Irene.

Portlight disaster relief efforts for 2011
My favorite disaster relief charity, Portlight.org, has posted a summary of their efforts during the hurricane season of 2011. Portlight mobilized in the wake of Hurricane Irene to help out in North Carolina, Delaware, and Maryland on cleanup efforts, food, and supply distribution. Portlight also provided financial assistance to survivors, including a commercial fisherwoman and single mother of two who lost her boat and home in the storm, after having been diagnosed with breast cancer two days before Irene struck. See the portlight blog for the full story; donations are always welcome. Wunderground is proud to be a major sponsor of Portlight again this year.

Next post
On Wednesday, I plan to look at 2011's worst hurricane--Hurricane Irene--and the lesson it should have given us regarding the hurricane vulnerability of New York City.

Jeff Masters

Hurricane

Updated: 04:14 PM GMT del 28 novembre 2011

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Storm surge barriers: the New England experience

By: JeffMasters, 06:22 PM GMT del 25 novembre 2011

Back in 1938, long before satellites, radar, the hurricane hunters, and the modern weather forecasting system, the great New England hurricane of 1938 roared northwards into Long Island, New York at 60 mph, pushing a storm surge more than 15 feet high to the coast. Hundreds of Americans died in this greatest Northeast U.S. hurricane on record, the strongest hurricane to hit the Northeast since the 1800s. A destructive storm surge of 13 feet (4 meters) barreled though Long Island Sound into Stamford, Connecticut, inundating the downtown region and causing heavy damage ($6 million in 1938 dollars.) Sixteen years later, a storm surge from Hurricane Carol of 1954 inundated the city again, causing $3.4 million in damage. In response to these twin storm surge disasters, work was begun in 1965 on a 17-foot high, $14 million (1965 dollars) hurricane barrier. Completed in 1969, the barrier across Stamford Harbor is high enough to protect the city from a storm surge of 14.8 feet above mean sea level. Had the barrier been in place during Hurricane Carol, the Army Corps of Engineers estimates damage to Stamford could have been reduced by 85%.


Figure 1. Bedford Street looking south towards Broad Street in Stamford, Connecticut, after the Great New England Hurricane of 1938. Image credit: stamfordhistory.org.


Figure 2. The storm surge from Category 2 Hurricane Carol in 1954 batters the Edgewood Yacht Club near Providence, Rhode Island. Image credit: NOAA Photo Library.

The Providence storm surge barrier
Stamford isn't the only New England city that suffered destructive storm surges from the 1938 and 1954 hurricanes. The 1938 hurricane brought a storm surge that covered the commercial district of Providence, Rhode Island with 8 feet (2.5 m) of water, causing $16.3 million in damage. On August 31, 1954, Hurricane Carol produced a storm surge of up to 14.4 feet (4.4 m) in Narragansett Bay, surpassing that of the New England Hurricane of 1938. The resulting storm surge flooded downtown Providence with 12 feet (3.7 m) of water. Some entire coastal communities were nearly destroyed, and damage was estimated at $25.1 million. In response to the devastation wrought by these storms, a $15 million hurricane barrier 25 feet (7.6 m) high was built across the 1000-foot (300 m) entrance to Providence Harbor between 1961 - 1966.


Figure 3. A ship passes through the Providence, Rhode Island storm surge barrier. Image credit: Douglas Hill, EngScD, P.E., Stony Brook University.

The New Bedford storm surge barrier
New Bedford, Massachusetts lies near the end of a narrow bay, and narrow bays and river estuaries can act as funnels that focus storm surges to extreme heights if the hurricane's direction of motion is aligned so that the surge propagates up the bottleneck. In fact, the shape of the coast near New Bedford makes it the most vulnerable portion of the U.S. coast for a hurricane storm surge. The highest theoretical storm surge produced by NOAA's SLOSH model for the U.S. is 38.5 feet above mean sea level, for a Category 4 hurricane hitting New Bedford. Destructive storm surges hit New Bedford during the 1938 hurricane and 1954's Hurricane Carol, the latter storm causing $8.3 million in flood damages. A hurricane barrier 23 feet (7 m) high and 4900 feet (1500 m) long across New Bedford Harbor was completed in 1966 at a cost of $19 million (1966 dollars.) The barrier separates the New Bedford Harbor from Buzzard's Bay, and successfully kept out the 8 foot (2.5 m) storm surge from Hurricane Bob in 1991, and a 6.5 foot (2 m) surge from the January 1997 Nor'easter.


Figure 4.The 4,900 foot-long New Bedford, Massachusetts storm surge barrier as seen using Google Earth. The city of New Bedford lies to the north (top) of this image.


Figure 5.The four regions of the U.S. theoretically prone to storm surges in excess of 33 feet at the coast. These Maximum of the Maximum Envelope Of Waters (MOM) SLOSH model plots are for a maximum strength hurricane hitting at high tide. A theoretical peak storm surge of 33 - 34 feet (pink colors) is predicted by the SLOSH model for New York City near the JFK Airport (upper left), for the Big Bend region of the Florida Gulf Coast (lower right), and for the Intracoastal Waterway north of Myrtle Beach, South Carolina (lower left). The highest theoretical surge occurs at New Bedford, Massachusetts (upper right): 38.5 feet for a Category 4 hurricane.

More storm surge barriers needed
Storm surge barriers in Stamford, New Bedford, and Providence have already proved their worth and prevented damages more than the cost of their construction. For example, the Stamford barrier kept out the storm surge from the December 1992 Nor'easter, which neighboring New York City suffered storm surge flooding of it subway system and roads that caused hundreds of millions in damage. Similar barriers in the Netherlands and England's Thames River have also proved their worth, and multi-billion dollar storm surge barriers are nearing completion in St. Petersburg, Russia and the Venice Lagoon in Italy. Many more such barriers will be needed world-wide in the coming decades, because of sea level rise.
Sea level rose an average of 7 inches (18 cm) during the 20th century. The 2007 report of the U.N.'s Intergovernmental Panel on Climate Change (IPCC) predicted global sea level rise of 0.6 - 1.9 feet (18 - 59 cm) by 2100--excluding the contribution from melting of the Greenland and Antarctic ice sheets. Several studies published since that report predict much higher levels of sea level increase will occur if one includes the melting from Greenland and Antarctica, For example, a 2008 paper published by Pfeffer et al. in Science concluded that the "most likely" range of sea level rise by 2100 is 2.6 - 6.6 feet (80 - 200 cm.) If these higher sea level rise estimates prove correct, storm surge damage could easily double of triple, particularly if climate change makes the strongest storms stronger. A Report to Congress by FEMA (1991) estimated that existing development on the U.S. coast would experience a 36 - 58% increase in annual damages for a 1-foot rise in sea level, and a 102 - 200% increase for a 3-foot rise. Much of this additional damage would result from storm surges riding on top of heightened sea levels. As I'll report on in future blog posts in this series, even if the sea level does not rise this century, there are three locations along the U.S. coast that should immediately begin planning to install hurricane storm surge barriers: New York City, Galveston/Houston, and Tampa Bay.

Jeff Masters

Hurricane

Updated: 09:25 PM GMT del 27 novembre 2011

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A strange 2011 Eastern Pacific hurricane season

By: JeffMasters, 04:25 PM GMT del 23 novembre 2011

The Eastern Pacific's late season surprise, Hurricane Kenneth, is falling apart nearly as fast as it intensified. Kenneth, now a Category 1 hurricane with 90 mph winds, was a powerful Category 4 storm with 145 mph winds yesterday, and was by far the strongest hurricane to appear so late in the year in either the Eastern Pacific or Atlantic Oceans. Kenneth is moving over colder water and into a region with higher wind shear, and will continue to deteriorate over the next few days. Kenneth is not a threat to any land areas.


Figure 1. GOES-West satellite image of Hurricane Kenneth taken at 11 am EST November 22, 2011. Image credit: NOAA Visualization Lab.

The 2011 Eastern Pacific hurricane season: a strange one
Hurricane season officially ends next week on November 30 in both the Atlantic and Pacific Oceans, and it is likely that we won't see any more named storms in either basin. It was a strange hurricane season in the Eastern Pacific, but in the opposite sense of the Atlantic's strange season. The 2011 Eastern Pacific hurricane season featured a well below-average number of named storms--eleven (fifteen is average). However, all but one of these storms reached hurricane strength, the highest proportion of hurricanes in a single season ever recorded. Six of the hurricanes became intense hurricanes, double the normal. An average Eastern Pacific hurricane season has 15 named storms, 8 hurricanes, and 3 intense hurricanes. It is common for an Eastern Pacific hurricane season to have fewer named storms than usual during a La Niña year, like this year. It is unusual to have so many hurricanes and intense hurricanes in a La Niña year. The only La Niña years to record so many intense hurricanes in the Eastern Pacific were 1971 and 1985 (six and eight intense hurricanes, respectively.) The strongest Eastern Pacific storm of 2011 was Hurricane Dora, which topped out as a Category 4 hurricane with 155 mph winds. The deadliest cyclone was Tropical Depression 12-E, which made landfall near the Mexico/El Salvador border on October 13. At least 105 people died in Central America due to TD 12-E's flooding rains. El Salvador recorded an astonishing 1.51 meters (4.96') of rain in a ten-day period due to TD 12-E and its remnants.


Figure 2. Tracks from the 2011 Eastern Pacific hurricane season.

Have a great holiday weekend, everyone, and I'll be back Friday with a new post.

Jeff Masters

Hurricane

Updated: 04:30 PM GMT del 23 novembre 2011

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Category 4 Kenneth the strongest East Pacific late-season hurricane on record

By: JeffMasters, 03:43 PM GMT del 22 novembre 2011

Hurricane Kenneth has intensified into an impressive Category 4 storm with 145 mph winds in the Eastern Pacific. Kenneth is by far the strongest hurricane to appear so late in the season in the Eastern Pacific; the previous record was held by Hurricane Winnie of December 5, 1983, a Category 1 storm with 90 mph winds. There has not been an Atlantic hurricane as strong as Kenneth this late in the season, either; the latest of the seven November major hurricanes in the Atlantic was Hurricane Kate of November 21, 1985 (120 mph winds). Since 1949, here have been just three named storms that have formed in the Eastern Pacific after November 18. These three storms were an unnamed tropical storm on November 27, 1951; Tropical Storm Sharon on November 27, 1971; and Hurricane Winnie on December 5, 1983.

Kenneth is over 27°C waters and under light wind shear of 5 - 10 knots, so could conceivably intensify further. However, I expect the storm has peaked, since it's tough for a hurricane to get much stronger than Kenneth's current intensity with ocean temperatures so close to the 26.5°C hurricane formation threshold. Satellite loops show an impressive storm with a large eye, good symmetry, and plenty of upper-level outflow. The relative lack of spiral bands and large, thick eyewall may qualify Kenneth to be a rare breed of hurricanes known as "annular". Annular hurricanes are a subset of intense tropical cyclones that are significantly stronger, maintain their peak intensities longer, and weaken more slowly than average tropical cyclones. The latest SHIPS model output indicates that Kenneth has passed the initial screening step to be considered an annular hurricane. Only 4% of all hurricanes are annular hurricanes.


Figure 1. Morning satellite image of Hurricane Kenneth.

Unnamed tropical storm from September 2 brings the Atlantic's 2011 tally to 19
Re-analysis has shown that a tropical disturbance that formed between Bermuda and Nova Scotia on September 2 briefly attained tropical storm status, according to an article posted yesterday by Ken Kaye at SunSentinel.com, quoting NOAA's lead seasonal hurricane forecaster Gerry Bell. The addition of the unnamed tropical storm to the record books brings this year's tally of named storms to nineteen, tying 2011 with 2010, 1995, and 1887 as the 3rd busiest year for tropical storms. Only 2005 and 1933 had more named storms since record keeping began in 1851. An average season has just eleven named storms. Here's my blog entry from September 2 on the unnamed tropical storm:

A well-organized low pressure system with a surface circulation but limited heavy thunderstorm activity due to high wind shear is 450 miles south of Halifax, Canada. This disturbance, (94L), is headed northeast out to sea, and is being given a 60% chance of developing into a tropical depression by NHC. 94L is under a high 25 - 30 knots of wind shear, but this shear is expected to fall to the moderate range, 10 - 20 knots, by Saturday morning. However, sea surface temperature will fall from 27°C today to 25°C Saturday morning underneath 94L, and the storm will have a very short window of time to get organized enough to get a name. At this point, it's really a subjective judgement call on whether or not 94L is already a tropical storm.

In addition, the Atlantic has gained one more hurricane for the year, as Nate was upgraded to a hurricane in post-season analysis. Nate hit Mexico's Bay of Campeche coast near Veracruz on September 11 as a weak tropical storm. The storm killed five people and caused minor damage near Veracruz. Nate brings this year's tally of hurricanes to seven, one hurricane above average.


Figure 2. True-color MODIS image of Tropical Storm Nate taken at 12:45 pm EDT Friday, September 9, 2011. At the time, Nate was a tropical storm with 50 mph winds. Image credit: NASA.

Invest 99L in the Atlantic moving over colder waters
In the Atlantic, Invest 99L, an extratropical storm in the middle Atlantic that is generating tropical storm-force winds, has moved over colder waters of 24°C and is looking less tropical than yesterday. The storm is moving northeastwards out to sea and over even colder waters, and is not a threat to any land areas. NHC is giving 99L a 10% chance of becoming a named subtropical storm.

Jeff Masters

Hurricane

Updated: 03:45 PM GMT del 22 novembre 2011

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Rare late-season Eastern Pacific hurricane forms

By: JeffMasters, 02:43 PM GMT del 21 novembre 2011

Tropical Storm Kenneth formed over the weekend in the Eastern Pacific, and intensified into a hurricane late this morning. We are well past the date for the usual formation of the season's last storm, since the African waves spawned by the African monsoon, which serve as low pressure "seeds" to get the atmosphere spinning and trigger formation of more than half of the Eastern Pacific's storms, are rare this time of year. Kenneth formed from some unusual wave-like motions in the atmosphere over the Eastern Pacific that were not associated with African tropical waves. Since 1949, here have been just three Eastern Pacific named storms that formed after November 18. These three storms were an unnamed tropical storm on November 27, 1951; Tropical Storm Sharon on November 27, 1971; and Hurricane Winnie on December 5, 1983. None of these storms hit land, though the 1951 storm grazed the Baja. If Kenneth grows stronger than a 90 mph hurricane, it will surpass Hurricane Winnie of 1983 as the strongest Eastern Pacific storm so late in the season. Kenneth is moving westwards out to sea, and should not be a threat to land.


Figure 1. Morning satellite image of Tropical Storm Kenneth taken at 7 am EST November 21, 2011. Image credit: NASA/GSFC.

Atlantic's Invest 99L could become Subtropical Storm Tammy
In the Atlantic, Invest 99L, an extratropical storm in the middle Atlantic that is generating tropical storm-force winds, has the potential to transition into a subtropical storm over the next day or two. The storm currently lacks a well-defined surface circulation. If it develops one, 99L would be called Subtropical Storm Tammy. The storm is over waters of 26°C, and these waters will cool to 24°C by Tuesday, as 99L moves northeastwards out to sea. These water temperatures are near the limit of where a subtropical or tropical storm can form. The storm is not a threat to any land areas.

Jeff Masters

Hurricane

Updated: 04:48 PM GMT del 21 novembre 2011

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Extreme weather and climate change: a new IPCC report

By: JeffMasters, 03:48 PM GMT del 18 novembre 2011

Extreme weather events are already being affected by human-caused climate change, and will increase in destructive power during the coming decades as huge cost, reported the United Nations Intergovernmental Panel on Climate Change (IPCC) today. The IPCC issues reports on the state of the scientific knowledge of climate change every six years, with the next full report due out in 2013. However, concern over the possible impact climate change may already be having on extreme weather events like heat waves, floods, and droughts prompted the IPCC to release their first-ever Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX). The SREX report was divided into two sections: how human-caused climate change has already affected extreme weather events, and predictions on how these events will change during the rest of the century. Here are some highlights on how the climate has already changed, according to the SREX report:

- Globally, cold days and nights have decreased, and warm days and nights have increased (90 - 100% chance).

- In many but not all regions of the globe, the length or number of heat waves has increased.

- Some areas have seen more intense and longer droughts, in particular, southern Europe and West Africa. However, droughts have become less frequent, less intense, or shorter in some areas, such as central North America and northwestern Australia.

- Heavy precipitation events have changed in some regions. There is at least a 2-in-3 probability that more regions have seen increases than decreases in heavy precipitation events.

- The historical data base on hurricanes and tropical cyclones is not good enough to tell if they have changed.

- The jet stream has shifted towards the poles, meaning that the tracks of rain-bearing low pressure systems have also shifted towards the poles.

- Rising sea levels have led to an increase in extreme coastal flooding events (66 - 100% chance).

- Damage from extreme weather events has increased. Increases in population and wealth, and the fact more people are living in vulnerable areas, is a major cause of this increase in damage. It is uncertain if climate change is partially responsible for the increase in damage.


Figure 1. Predicted return periods for 1-day extreme precipitation events that occurred, on average, only once every 20 years between 1981-2000. A decrease in return period implies more frequent extreme precipitation events (i.e., less time between events on average). For Eastern North America, a 1-in-20 year heavy rain event is predicted to become a 1-in-7 to 1-in-9 year event by the end of the century, according to these climate model predictions. The box plots show results for regionally averaged projections for two time horizons, 2046 to 2065 and 2081 to 2100, as compared to the late-20th-century, and for three different emissions scenarios--a scenario where humans emit relatively little CO2 and other heat-trapping gasses (B1, blue bars), and two higher-emission scenarios (A1B and A2, green and red bars). Humanity is currently on a pace to emit more CO2 than the highest emission scenario shown here. Results are based on 14 climate models that contributed to the 2007 IPCC report. The level of agreement among the models is indicated by the size of the colored boxes (in which 50% of the model projections are contained), and the length of the whiskers (indicating the maximum and minimum projections from all models). Values are computed for land points only. The “Globe” inset box displays the values computed using all land grid points. Averaged over all areas of the globe, a 1-in-20 year heavy rain event is predicted to become a 1-in-8 to 1-in-12 year event by the end of the century. Image credit: The IPCC Special Report on Managing the Risks of Extreme Events and Disasters (SREX), 2011.

Here are some highlights of the forecasts for the future from the 2011 SREX report:

- A 1-in-20 year hottest day is at least 66% likely to become a 1-in-2 year event by the end of the 21st century in most regions, except in the high latitudes of the Northern Hemisphere, where it is likely to become a 1-in-5 year event.

- For Eastern North America, a 1-in-20 year heavy rain event is predicted to become a 1-in-7 to 1-in-9 year event by the end of the century.

- For Eastern North America, a maximum high temperature that occurred only once every 20 years during 1980 - 2000 is predicted to occur between once every three years and once per year by 2100.

- Extreme high temperature readings that occur once every 20 years will increase by 1°C to 3°C (1.8°F - 5.4°F) by mid-21st century and by about 2°C to 5°C (3.6°F - 9°F) by late-21st century.

- It is at least 66% likely that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase in the 21st century over many areas of the globe. This is particularly the case in the high latitudes and tropical regions, and in winter in the northern mid-latitudes. There is medium confidence that, in some regions, increases in heavy precipitation will occur despite projected decreases of total precipitation in those regions.

- Heavy rainfalls associated with tropical cyclones are at least 66% likely to increase with continued warming, and the maximum winds will increase. The total number of these storms is likely to remain about the same or decrease.

- There is medium confidence that droughts will intensify in the 21st century in some seasons and areas. Southern Europe and the Mediterranean region, central Europe, Central North America, Central America and Mexico, northeast Brazil, and southern Africa are at particular risk.

- In some regions, the main driver for increased damages from extreme weather events will not be climate change, but increases in population and wealth and vulnerability.

Intoducing climatecommunication.org
For those of you seeking detailed information on the research linking extreme weather events to climate change, I recommend a new website dedicated to improving communication of climate change information to the public, media, and policy makers, climatecommunication.org. The group is led by Susan Joy Hassol, a veteran climate change communicator, analyst, and author known for her ability to translate science into English, making complex issues accessible to policymakers and the public. Climatecommunication.org has put together an overview of extreme weather and climate change that I find a helpful resource when I am looking for the latest research results on the subject. I serve on their advisory board, along with a number of leading climate scientists.


Figure 2. Still image of the Bangkok, Thailand floods of October - November, 2011, as seen on the inaugural episode our new bi-monthly Extreme Weather video series.

Wunderground launches new Extreme Weather video series
Wunderground now features a new, twice-monthly Extreme Weather video series from GREEN.TV, with the latest reports and analysis on extreme weather around the world. From droughts to hurricanes to blizzards to flooding, Extreme Weather will cover the story and the science behind the events to try to understand their causes and consequences. The Extreme Weather series is sponsored by Vestas, the world's leading wind turbine manufacturer. The inaugural episode, launched yesterday, features video of the great Thailand flood, destructive floods in Italy, the $3 billion Northeast U.S. snowstorm of October 29 - 30, the massive Bering Sea, Alaska blizzard of November 9, the Texas drought, and the launch of a new polar-orbiting weather satellite. Look for a new video every two weeks on our Climate Change Videos page.

Resources
For those of you who haven't seen it, my top "must-read" post of 2011 is called, 2010 - 2011: Earth's most extreme weather since 1816?. Back in June, I went through the ridiculous barrage of extreme weather events the planet saw in 2010 and early 2011, and concluded: But it is highly improbable that the remarkable extreme weather events of 2010 and 2011 could have all happened in such a short period of time without some powerful climate-altering force at work. The best science we have right now maintains that human-caused emissions of heat-trapping gases like CO2 are the most likely cause of such a climate-altering force.

Wunderground's climate change blogger, Dr. Ricky Rood, has some thoughtful observations on the communication of the extreme weather/climate change link published in earthzine magazine titled, Changing the Media Discussion on Climate Change and Extreme Weather.

Jeff Masters

Climate Change

Updated: 05:48 PM GMT del 18 novembre 2011

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October 2011 the globe's 8th warmest on record

By: JeffMasters, 01:38 PM GMT del 16 novembre 2011

October 2011 was the globe's 8th warmest October on record, according to the National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies also rated October the 8th warmest on record. The top ten warmest Octobers since record keeping began in 1871 have all occurred since 1997. October 2011 global land temperatures were the 2nd warmest on record, and ocean temperatures were the 11th warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere near average, the 19th or 12th warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH).

Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the October 2011 Global Weather Extremes Summary.


Figure 1. Departure of temperature from average for October 2011. Image credit: National Climatic Data Center (NCDC).

A warm October with few extremes for the U.S.
In the contiguous U.S., where extreme weather has been the norm this year, October was remarkably normal. October 2011 ranked as the 33rd warmest October in the 117-year record. Extremes in temperature were hard to find, with no states recording a top-ten coldest or warmest October. Three states had a top-ten driest October--Louisiana, Missouri, and Iowa. Two states had a top-ten wettest October--New Hampshire and Massachusetts. Precipitation over Texas was near normal in October, making it the first month since February that was not a top-ten driest month for the state. Nevertheless, 90% of Texas remained under extreme to exceptional drought as of November 8, according to the U.S. Drought Monitor. The most significant weather event of the month in the U.S. was the October 29 - 30 Nor'easter that dumped up to 32" of snow on the Northeast, causing at least $3 billion in damage.

A weak La Niña continues
A weak La Niña event continues in the equatorial Pacific, where sea surface temperatures have ranged between 0.8 - 1.1°C below average during the first half of November. The impacts of a La Niña on U.S. weather are well-defined. It is likely that the drought in the South, especially Texas, will continue, along with above average temperatures. The Northwest can expect cooler than average temperatures, as well as the potential for another winter with a heavy snowpack across the western United States.

Arctic sea ice extent second lowest on record
Arctic sea ice extent was at its second lowest on record in October, behind 2007, according to the National Snow and Ice Data Center. October 2011 sea ice extent was 23.5% below the 1979 - 2000 average. Sea ice extent retreated to its lowest value on record during the second week of November, thanks in part to a powerful 943 mb blizzard that brought hurricane-force winds to the Chukchi Sea between Siberia and Russia, compacting and breaking up the sea ice there. Sea ice records date back to 1979.

Eastern Pacific hurricane season not over yet?
Both the tropical Atlantic and Eastern Pacific Oceans are quiet this week, and we are well past the date for the climatological formation of the season's last storm in both basins, particularly in the Eastern Pacific. A major reason for the lack of late-season activity in the Eastern Pacific is due to the cessation of African waves spawned by the African monsoon, which serve as low pressure "seeds" to get the atmosphere spinning and trigger formation of a tropical cyclone. However, the four top models for predicting formation of tropical storms unanimously agree that a tropical storm will form in the Eastern Pacific early next week, thanks to some unusual wave-like motions in the atmosphere that are generating low pressure systems over the Eastern Pacific, similar to African waves. The GFS model is forecasting that we will get not one, but two tropical storms forming in the Eastern Pacific over the next two weeks. Tropical storms are very rare in the Eastern Pacific this late in the year. Since 1949, here have been just three named storms that have formed after November 18. These three storms were an unnamed tropical storm on November 27, 1951; Tropical Storm Sharon on November 27, 1971; and Hurricane Winnie on December 5, 1983. None of these storms hit land, though the 1951 storm grazed the Baja. Next week's storm, if it forms, is expected to move west-northwest, parallel to the Mexican coast, but it is uncertain if it might pose a landfall threat or not.

Jeff Masters

Climate Summaries

Updated: 01:43 PM GMT del 16 novembre 2011

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Thailand's flood gradually subsiding; climate change increasing Thai flood risk

By: JeffMasters, 02:56 PM GMT del 14 novembre 2011

Unprecedented flood waters continue to besiege Thailand and its capital city of Bangkok this November. Heavy monsoon and tropical cyclone rains from July through October, enhanced by La Niña conditions, have led to extreme flooding that has killed 506 people and caused that nation's most expensive natural disaster in history, with a cost now estimated at $9.8 billion by re-insurance company AON Benfield. Thailand's previous most expensive natural disaster was the $1.3 billion price tag of the November 27, 1993 flood, according to the Centre for Research on the Epidemiology of Disasters (CRED). The floodwaters this year have hit 83% of Thailand's provinces, affected 9.8 million people, and damaged approximately 25% of the nation's rice crop. Thailand is the world's largest exporter of rice, accounting for 30% of the global total, and the flood has helped trigger an increase in world rice prices in recent months. Fortunately, the Food and Agriculture Organization of the U.N. reports that overall global food prices have been steadily falling since June, thanks in part to increases in wheat and corn production elsewhere in the world. Food prices had reached their highest levels since the late 1970s early in 2011.


Figure 1. The Advanced Land Imager (ALI) on NASA's Earth Observing-1 (EO-1) satellite acquired this pair of before-and-after natural-color images of Ayutthaya, Thailand, on October 23, 2011, and July 11, 2011. In both images, the Chao Phraya River curves through the outskirts of the city (north is to the left in these images). In October, however, the river has overflowed onto nearby floodplains. Fields, roads, and buildings have all been submerged by sediment-clogged flood water. Image credit: NASA Earth Observatory.

The Thailand floods in historical context
Large floods have occurred along Bangkok's Chao Phraya River in 1942, 1978, 1980, 1983, 1995, 1996, 2002, and 2006. The 1942 flood is considered to be the worst flood in modern times. Since 1942, land subsidence, sea level rise, deforestation, urbanization, and removal of wetlands have made floods more likely. However, this has been offset to a large degree by the construction of a series of dams in the upper watershed of the Chao Phraya River basin--including the Bhumibol Dam (1964) and Sirikit Dam (1971). According to wunderground's weather historian Christopher C. Burt, who blogged about the Thailand flood on October 29, the flood of 2011 rivals or exceeds the great flood of 1942 in terms of depth of the flood waters, and the 2011 Thailand flood is perhaps the greatest flood ever to swamp a city so large (population 10 million) in world history. The last time a flood of such a great magnitude affected a city so large occurred in 2004 in Dhaka, Bangladesh, which also has a population near 10 million. Dhaka was almost completely submerged in during massive monsoon floods in the summer of 2004.

The estimated $9.8 billion in damage to Thailand from the 2011 flood is nearly 4% of the country's GDP. Hurricane Katrina cost the U.S. about 0.7% of its GDP, so the Thailand floods can be thought of as a disaster five times worse than Katrina for that country. The most expensive natural disaster worldwide since 1970 in relation to a country's size and economy (for disasters with a high death toll) was the 2010 earthquake in Haiti, according to the Inter-American Development Bank. Haiti's earthquake cost $8 billion, which was 115% of Haiti's GDP. The most expensive flooding disasters in the world since 1970, relative to GDP, both occurred in Honduras. Category 5 Hurricane Mitch of 1998 did damage equivalent to 81% of GDP, and Category 3 Hurricane Fifi of 1974 cost 59% of GDP to Honduras.

Short range forecast: gradual improvement
Fortunately, the monsoon has been quiet so far in November over Thailand, and the latest GFS model precipitation forecast show little additional rain over the country during the coming week. One wild card might be the appearance of a typhoon; November typhoons often affect Thailand. However, the reliable models for predicting typhoon development are currently not forecasting any typhoon activity in the Western Pacific over the coming seven days.


Figure 2. Predicted global sea level rise for 2100 from three different studies.

Forecast for the remainder of the 21st century: more mega-floods for Bangkok
Bangkok lies in the Chao Phraya River basin, which covers about 35% of the country, and has an average elevation just 1 - 2 meters above sea level. Obviously, sea level rise, which averaged 7 inches world-wide during the 20th century, and is predicted to be at least that high during the 21st century, is a huge concern for Thailand. Loss of land due to a sea-level rise of .5 m and 1.0 m could decrease national GDP by 0.36% and 0.69% (US$300 to 600 million) per year, respectively (Ohno, 2001). Higher sea levels also block the flow of flood waters out of the Chao Phraya River, backing up these waters into the city, putting stress on levees and raising flood heights. Another major concern of climate change is the increase in rainfall expected in a warmer world. A 2010 study by the World Bank found that a global temperature rise of 1.2 - 1.9°C would likely increase precipitation over Thailand by 2 - 3%. This extra rainfall, when combined with predicted levels of sea level rise and land subsidence due to groundwater pumping, would likely make a 1-in-50 year flood occur once every fifteen years by the end of the century. Since the flood control system in Bangkok is "generally designed to protect against 1-in-30-year floods", the report concluded that "people living in Bangkok will be facing more frequent events that significantly disrupt daily life." This study assumed that sea level rise by 2100 would be what the IPCC predicted in 2007: 0.6 - 1.9 feet. A number of studies published since that report are predicting much higher levels of sea level increase: 3 - 6 feet (1 - 2 meters) by 2100. If these higher sea level rise estimates prove correct, mega-floods like the 2011 flood will occur several times per decade in Bangkok by the end of the century--unless the Thais can engineer a massive sea wall to keep the ocean at bay.

The city and national planners have plans to add further flood protection, which has been planned and budgeted through 2014. The long-term land use plan until 2057 calls for adding new buffer zones and canals to re-route flood waters. Intentional flooding of agricultural lands upstream of Bangkok during major floods will also be used to help reduce the flood profile in Bangkok.

References
Michael Lemonick of ClimateCentral.org has an op-ed in the L.A. Times called "Thailand's Heart Attack", where he shows how climate change increased the odds of the 2011 mega-flood in Thailand. He makes the point, "Increasing load of greenhouse gases we're pumping into the atmosphere doesn't 'cause' extreme weather. But it does raise the odds, just as a diet of triple bacon cheeseburgers raises the odds of heart disease."

Ohno, E., 2001: Economic evaluation of impact of land loss due to sea-level rise in Thailand. Proceedings of the APN/SURVAS/LOICZ Joint Conference on Coastal Impacts of Climate Change and Adaptation in the Asia Pacific Region, 14-16th November 2000, Kobe, Japan, Asia Pacific Network for Global Change Research, 231-235.

World Bank, 2010, Climate risks and adaptation in Asian coastal megacities: a synthesis report

Jeff Masters

Flood Climate Change

Updated: 06:37 PM GMT del 14 novembre 2011

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Sean brushes Bermuda; largest wave ever surfed; Tipton tornado an EF-4

By: JeffMasters, 03:26 PM GMT del 11 novembre 2011

Tropical Storm Sean brushed by Bermuda this morning, bringing winds near tropical storm force to the island. Top sustained winds at the Bermuda airport were 37 mph this morning, and a gust of 56 mph occurred at 4:38 am AST. Dry air disrupted the circulation of Sean before it reached Bermuda, and the island picked up just 0.08" of rain as of 10 am AST today. Sean is headed northeastward, out to sea, and will cease to exist later today or on Saturday. Sean may not be the last storm of the season, however. The most recent runs of the GFS, NOGAPS, and ECMWF models all predict an extratropical storm capable of transitioning to a subtropical or tropical storm will form in the middle Atlantic late next week. If such a storm did form, it would be called Tammy, and would not threaten any land areas.


Figure 1. A wet, windy day in Bermuda: morning webcam image from the island. Image credit: freddiebda's webcam.

Largest wave ever surfed
A new world record was set this week for the largest wave ever surfed. On Tuesday, November 8, Hawaiian big wave rider Garrett McNamara caught a 90-foot (27 meter) wave during a tow-surfing session just offshore of the small fishing village of Nazare, Portugal. An undersea canyon 5000 meters deep runs very close to the shore, and the unique bathymetry is known to create unusually large waves when west-northwest swells affect the coast. On Tuesday, an approaching cold front extending southwards from a low pressure system centered just south of Iceland generated strong winds off the coast of Portugal, and a west-northwest swell of 8 meters (26'). The canyon generated three big waves in excess of 60 feet that day, and McNamara was able to catch the tallest, 90-foot wave. The previous record highest wave surfed was a 77-foot (23 meter) wave caught in 2008 at Cortes Bank off the coast of Southern California by Mike Parsons.


Video 1. Surfer Garrett McNamara rides a 90-foot wave off the coast of Portugal on November 8, 2011, setting a new world record for the largest wave ever riden.

November 7 Tipton, Oklahoma tornado rated an EF-4
The powerful tornado that hit Tipton, Oklahoma on November 7 has been rated an EF-4 by the National Weather Service. The Tipton tornado hit two Oklahoma Mesonet stations and destroyed them; the Tipton mesonet site measured winds of 86.4 mph and the Fort Cobb site measured winds of 91.4 mph before destruction. The tornado was one of a family of six spawned that day by the parent supercell thunderstorm. The Tipton tornado is the first November EF-4 tornado in Oklahoma's history, and one of only twenty EF-4 or stronger November tornadoes observed in the U.S. since 1950, according to the Tornado History Project. There have been twelve December EF-4 tornadoes and two December EF-5 tornadoes observed in the U.S. since 1950. The confirmed tornado count for 2011 is 1543, putting this year in third place so far for most tornadoes, behind the 1692 tornadoes observed in 2004 and 1817 tornadoes in 2008. By the time the year ends, 2011 should wind up with 1600 - 1700 confirmed tornadoes.


Figure 2. Time series showing the weather at the Fort Cobb, OK mesonet station during passage of the November 7, 2011 Tipton tornado. A wind gust of 91.4 mph and pressure spike down to 946 mb occurred during the tornado's passage. Image credit: NWS/Norman Oklahoma.

Have a great weekend, everyone, and I'll be back Monday with a new post.

Jeff Masters

Tornado Hurricane

Updated: 10:25 PM GMT del 11 novembre 2011

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Alaska blizzard pushes 8-foot storm surge into Nome; Sean heads towards Bermuda

By: JeffMasters, 02:47 PM GMT del 10 novembre 2011

The most powerful storm to affect the Bering Sea coast of Alaska since 1974 is slowly winding down today, after pounding Alaska's west coast and Eastern Siberia with hurricane-force winds, a destructive storm surge more than 8 feet high, waves up to 40 feet high, and heavy snow. The highest wind gust recorded during the storm, 89 mph, was at Wales at the western tip of the Seward Peninsula, which forms the U.S. side of the Bering Strait. Hurricane force gusts were observed at seven locations in Alaska:

Cape Lisburne... 81 mph at 7 am Wed
Gambell... ... ... 74 mph at 6 pm Tue
Kotzebue... ... ..74 mph at 6 am Wed
Point Hope... ... 78 mph at 5 am Wed
Savoonga... ... ..76 mph at 7 pm Tue
Tin City... ... ..85 mph at 12 am Wed
Wales... ... ... ..89 mph at 1:42 am Wed

A storm surge of 8.6 feet hit Nome, Alaska near 9 pm EST last night, pushed inland by sustained winds that reached 45 mph, gusting to 61 mph. Large waves on top of the surge encrusted with sea ice battered the coast, causing extensive damage and coastal flooding. Significant wave heights at the Bering Sea buoy north of the Aleutian Islands reached 40 feet during the peak of the storm. The last time Nome, Alaska saw a storm this strong was November 11 - 12 1974, when the city experienced sustained winds of 46 mph with gusts to 69 mph, a pressure that bottomed out at 969 mb, and a storm surge of 13 feet. The center of yesterday's storm moved ashore over eastern Siberia near 12 UTC with a central pressure of 945 mb, and later bottomed out with a pressure of 943 mb. The storm's central pressure had risen to 958 mb this morning, with the center of the storm now located north of Siberia over the Arctic.


Figure 1. MODIS satellite image taken November 8, 2011, of the 943 mb Bering Sea superstorm that affected Alaska and Siberia. Image credit: NASA.


Figure 2. Observed storm surge at Nome, Alaska (green line). MLLW = Mean Lower Low Water, the water level at the lowest tide of the month. The top storm surge of 8.6 feet occurred near 02 GMT this morning (9 pm EST November 9, 2011.) Image credit: NOAA Tides and Currents.

My related blog posts:
Climate change likely to worsen erosion along the Alaska coast
The future of intense winter storms

Tropical Storm Sean
Tropical Storm Sean is on the move towards the northeast, towards a brush with Bermuda. Infrared satellite loops reveal that Sean has not changed much in organization this morning. The storm has a respectable amount of heavy thunderstorm activity near its center that is relatively shallow, and Sean has at times been able to close off an eyewall, and has a ragged-looking eye. Bermuda radar shows one strong rain band from Sean has affected the island, with the bulk of Sean's heavy thunderstorms well to the island's southwest. Sustained winds at the Bermuda airport have been under 30 mph this morning, and Bermuda picked up 0.08" of rain yesterday, and 0.24" as of 9 am EST today. Sustained winds at buoy 41048, about 300 miles west of Bermuda were 40 mph at 7:50 am EST. Strong upper-level winds out of the west are creating about 20 knots of wind shear over Sean, which is low enough to allow some slow development. Ocean temperatures have fallen to 25°C (77°F), which just below the 26°C threshold typically needed for a tropical storm to maintain its strength.


Figure 2. Morning satellite image of Tropical Storm Sean.

Forecast for Sean
The latest SHIPS model forecast predicts wind shear will remain about where it is now through Friday morning. However, ocean temperatures will gradually cool to 24°C during this time, and it is questionable whether Sean will have a favorable enough environment to strengthen into a hurricane. The computer models show little development of Sean, with none of our reliable models predicting it will become a hurricane. Bermuda is the only land area that need concern itself with Sean, as the storm is now caught in a trough of low pressure that will accelerate the storm to the northeast. The center of Sean could pass close enough to Bermuda to bring the island heavy rain squalls and sustained winds of 40 - 45 mph on Friday. NHC is giving a 52% chance that Bermuda will receive tropical storm-force winds of 39 mph. Wind shear will rise to 30 - 50 knots on Friday, which should be able to rip the storm apart by Saturday.

Jeff Masters

Winter Weather Hurricane

Updated: 01:33 AM GMT del 10 Febbraio 2012

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Historic hurricane-force blizzard pounds Alaska and Siberia

By: JeffMasters, 02:53 PM GMT del 09 novembre 2011

The most powerful storm to affect the Bering Sea coast of Alaska in 37 years is pounding Alaska's west coast and Eastern Siberia with hurricane-force winds, a destructive storm surge up to 7 feet high, waves up to 35 feet high, and blinding snow. Tin City on the west coast of Alaska north of Nome recorded sustained winds of 70 mph, gusting to 81 mph, at 1:55 am local time this morning, and hurricane-force winds are likely affecting much of the open waters of the Bering Sea. A storm surge of 6 feet hit Nome, Alaska this morning, pushed inland by sustained winds that reached 45 mph, gusting to 61 mph. A even higher storm surge is predicted for this evening (Figure 3.) The last time Nome, Alaska saw a storm this strong was November 11 - 12 1974, when the city experienced sustained winds of 46 mph with gusts to 69 mph, a pressure that bottomed out at 969 mb, and a storm surge of 13 feet that pushed beach driftwood above the previous high storm tide mark set in 1913. The center of today's storm moved ashore over eastern Siberia near 12 UTC with a central pressure of 945 mb. The storm has likely peaked in strength, and will gradually weaken as it moves northeast into the Arctic.


Figure 1. Visible satellite image of the Bering Sea superstorm at 7 pm EST November 8, 2011. Image credit: National Weather Service.


Figure 2. Observed storm surge at Nome, Alaska (green line). MLLW = Mean Lower Low Water, the water level at the lowest tide of the month. Image credit: NOAA Tides and Currents.


Figure 3. Predicted storm surge (yellow-brown line) for Nome, Alaska for today's Bering Sea storm. The black line is the predicted storm tide--the water level reached as a result of the storm surge and the natural tidal cycle. Tidal range at Nome is normally less than 2 feet between low tide and high tide (green line.) MAT = Maximum Astronomical Tide, MLLW = Mean Lower Low Water. Image credit: National Weather Service.


Figure 4. Predicted storm surge for today's storm, as forecast by the Ocean Prediction Center's Extratropical Storm Surge Model. Image credit: NOAA Environmental Visualization Lab.

Climate change likely to worsen erosion along the Alaska coast
Arctic sea ice was at its 2nd lowest extent on record during October 2011, according to the National Snow and Ice data Center. Much of the missing ice this fall is along the Chukchi Sea coast of Northwest Alaska, where today's massive storm is hitting. When sea ice disappears, coastlines become more susceptible to battering waves. This is particularly common during the fall season, not only because sea ice extent is usually at its minimum, but fall is when storms tend to be stronger with higher storm surges. Recent coastal destruction has already forced residents of the Alaskan town of Shishmaref to vote to abandon their village. More than half the residents of the nearby village of Kivalina (population 400) were forced to evacuate in September 2007, when 25 - 40 mph winds drove a four foot storm surge into the town. The U.S. Army Corps of Engineers completed a $16 million sea wall and shore fortifications in 2009 to protect the town, and Kivalina is trusting these protections during today's storm; no evacuations occurred. As of 11 am EST today, Kivalina has seen top sustained winds of 51 mph, gusting to 71 mph.


Figure 5. Kivalina, Alaska in 2005. Note how the homes on the right side of the image are perched precariously close to the ocean, due to erosion that has eaten away the shore. Image credit: Millie Hawley.

As sea ice continues to decrease in coming years, leaving more ocean surface exposed to air, more moisture and heat will be available to power storms. As I discussed in detail in my post, The future of intense winters storms, multiple studies have documented a significant increase in the number of intense extratropical cyclones with central pressures below 970 or 980 mb over the North Pacific and Arctic in recent decades. Computer climate models predict predict a future with fewer total winter storms, but a greater number of intense storms; up to twelve additional intense Northern Hemisphere cold-season extratropical storms per year are expected by the end of the century if we continue to follow our current path of emissions of greenhouse gases. These stronger storms will bringer higher winds and higher storm surges to coastal areas of Alaska and the Arctic over the remainder of the 21st century, resulting in increased erosion and flooding of low-lying areas. Contributing to the erosion will be sea level rise. Kivalina, which lies on a narrow barrier island in the Chukchi Sea, has been losing up to 8 feet of shore each year due to erosion, and the long-term survival of the island is in serious doubt. Plans have been drawn up by the Army Corps of Engineers to relocate the city to the mainland, but finding funding for the $100 - $400 million dollar move has been problematic. The city of Kivalina and a federally recognized tribe, the Alaska Native Village of Kivalina, sued Exxon Mobil Corporation, eight other oil companies, 14 power companies, and one coal company in a lawsuit filed in federal court on February 26, 2008, claiming that the large amounts of greenhouse gases these companies are responsible for contribute to global warming that threatens the community's existence. The lawsuit estimates the cost of relocation at $400 million.


Figure 6. The Kivalina sea wall as seen in 2007. Image credit: City of Kivalina.


Figure 7. The projected change in intense wintertime extratropical storms with central pressures < 970 mb for the Northern Hemisphere under various emission scenarios. Storms counted occur poleward of 30°N during the 120-day season beginning November 15. A future with relatively low emissions of greenhouse gases (B1 scenario, blue line) is expected to result in an additional four intense extratropical storms per year, while up to twelve additional intense storms per year can be expected in a future with high emissions (red and black lines). Humanity is currently on a high emissions track. Figure was adapted from Lambert and Fyfe (2006), and was taken from Weather and Climate Extremes in a Changing Climate, a 2009 report from the U.S. Global Change Research Program (USGCRP).

Tropical Storm Sean
Tropical Storm Sean became fully tropical yesterday as it stayed stationary 400 miles southwest of Bermuda. Infrared satellite loops reveal that Sean increased in organization this morning, with a cloud-free center now getting walled off from the dry air to Sean's west. The storm has a respectable amount of heavy thunderstorm activity near its center that is relatively shallow, and the tops of its thunderstorms extend up only to about the 300 mb level. Normally, a tropical storm extends up to about 200 mb. The shallow nature of Sean's thunderstorms mean that the storm is less vulnerable to wind shear than normal, since the storm is not feeling the strongest winds aloft. Bermuda radar shows one strong rain band from Sean has affected the island, with the bulk of Sean's heavy thunderstorms well to the island's southwest. Sustained winds at the Bermuda airport have been under 30 mph this morning, and Bermuda picked up just 0.08" of rain yesterday. Sustained winds at buoy 41048, about 300 miles west of Bermuda were 31 mph at 6:50 am EST. Strong upper-level winds out of the west are creating about 20 knots of wind shear over Sean, which is low enough to allow some slow development. Ocean temperatures are near 26.5°C (80°F), which is right at the boundary of being warm enough to support tropical storm formation.

Forecast for Sean
Sean will drift slowly west today, then turn north on Thursday. The latest SHIPS model forecast predicts wind shear will remain about where it is now through Friday morning, which should allow Sean to slowly intensify to a 60 mph storm. The computer models show little development of Sean, with none of our reliable models predicting it will become a hurricane. Bermuda is the only land area that need concern itself with Sean, as a trough of low pressure is expected to absorb the storm on Thursday night and lift it quickly to the north and then northeast. The center of Sean could pass close enough to Bermuda to bring the island heavy rain squalls and sustained winds of 40 - 45 mph on Thursday and Friday. NHC is giving a 31% chance that Bermuda will receive tropical storm-force winds of 39 mph. High wind shear should destroy Sean on Friday.


Figure 8. MODIS image of the hybrid low named "Rolf" in the Mediterranean Sea at 11:10 UTC November 9, 2011. Image credit: NASA.

Powerful "Medicane" hits France
A hybrid low pressure system pounded Southeast France yesterday, bringing heavy rains, hurricane-force winds gusts, and significant coastal flooding. The storm began over the weekend as an extratropical storm named "Rolf", but then stalled out over the relatively warm waters of the Mediterranean, acquiring tropical characteristics. Heavy thunderstorms similar in intensity to what one would get in a tropical storm built up, and Rolf developed sustained winds above tropical storm force. These sort of hybrid extratropical/tropical storms that form over waters colder than 22°C are sometimes called "Medicanes", and can cause substantial damage. Rolf brought heavy rains in excess of 400 mm (15.7") over the past 4 days to the department of Var, north of Toulon. A wind gust of 95 mph was recorded at 21 UTC November 8 at Porquerolles Island, south of the city of Toulon. French radar shows heavy rains from Rolf are continuing to affect Southeast France and the island of Corsica. Water temperatures off the south coast of France are near 17°C (63°F), far below the 26°C threshold usually needed to sustain a tropical storm.

Resources
Youtube video of high surf in Cannes along the south coast of France
Local news video showing coastal flooding and damage

Jeff Masters

Sea Ice Winter Weather Hurricane

Updated: 02:18 AM GMT del 10 novembre 2011

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Sean, rare Mediterranean hybrid, and AK superstorm forms; quakes and tornadoes in OK

By: JeffMasters, 03:52 PM GMT del 08 novembre 2011

Subtropical Storm Sean formed this morning between Bermuda and the Bahamas. Sean's formation brings this year's tally of named storms to eighteen, tying 2011 with 1969 as the 6th busiest Atlantic hurricane season since record keeping began in 1851. Only 2005, 1933, 1995, 1887, and 2010 have had more named storms. However, 2011 has had an unusually low percentage of its named storms reach hurricane strength. We've had an average number of hurricanes--six--meaning that only 33% of this year's named storms have made it to hurricane strength. Normally, 55 - 60% of all named storms intensify to hurricane strength in the Atlantic. There have been three major hurricanes in 2011, which is one above average, and the total Accumulated Cyclone Energy (ACE)--a measure of the destructive potential of this season's storms--has been about 20% above average. The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is no doubt at least partially responsible for the unusually high count of named storms, but near-average number of hurricanes and ACE.


Figure 1. The subtropical disturbance that became Subtropical Storm Sean, as seen at 1 pm EST November 7, 2011. Image credit: NASA.

Infrared satellite loops reveal that Sean has developed a respectable amount of heavy thunderstorm activity near its center that is increasing in intensity and areal coverage. While the low-level circulation center is exposed to view, a band of thunderstorms is trying to wrap around and close of the center. If this occurs, more substantial strengthening can occur, since the center will be walled off from the dry air that is currently interfering with development. Bermuda radar shows weak rain bands from Sean rippling across the island, with the strongest rain showers well to the island's southwest. Sustained winds at the Bermuda airport have been under 30 mph this morning. Sustained winds near tropical storm force were occurring this morning at buoy 41048, about 300 miles west of Bermuda. Winds at the buoy were 38 mph, gusting to 47 mph at 6:50 am EST. Strong upper-level winds out of the west are creating about 20 knots of wind shear over Sean, which is low enough to allow some slow development. Sean is a relatively shallow storm, and the tops of its thunderstorms extend up only to about the 300 mb level. Normally, a tropical storm extends up to about 200 mb. The shallow nature of Sean's thunderstorms mean that the storm is less vulnerable to wind shear than normal, since the storm is not feeling the strongest winds aloft. Ocean temperatures are near 26.5°C (80°F), which is right at the boundary of being warm enough to support tropical storm formation.

Forecast for Sean
Sean will drift slowly west or northwest today and Wednesday. The latest SHIPS model forecast predicts wind shear will remain about where it is now through Thursday morning, which should allow Sean to slowly intensify to a 50 mph storm. If Sean can make the transition to a fully tropical storm, more significant intensification can occur. The computer models show little or no development of Sean, with none of our reliable models predicting it will become a hurricane. Bermuda is the only land area that need concern itself with Sean, as a trough of low pressure is expected to absorb the storm on Thursday and lift it quickly to the north or northeast. The center of Sean could pass close enough to Bermuda to bring the island heavy rain squalls and sustained winds of 40 - 45 mph on Thursday and Friday. NHC is giving a 28% chance that Bermuda will receive tropical storm-force winds of 39 mph. High wind shear should destroy Sean on Friday.


Figure 2. MODIS image of the hybrid low named "Rolf" in the Mediterranean Sea at 10:30 UTC November 8, 2011. Image credit: NASA.

Unusual tropical storm-like low forms off coast of France
An unusual hybrid low pressure system has formed in the Mediterranean Sea, about 100 miles south of the coast of France. The low began as an extratropical storm named "Rolf", but has stalled out over the relatively warm waters of the Mediterranean over the past two days, and has acquired tropical characteristics. Heavy thunderstorms have built over the northeast portion of the low, and the storm has a symmetric spiral shape with a cloud-free center, like a tropical storm. The Navy is calling this system Invest 99L. The National Hurricane Center is not responsible for the Mediterranean Sea, so they are not issuing any products for 99L. NOAA's Satellite and Information Service (NESDIS) is giving 99L a tropical classification based on its satellite presentation, with winds in the 40 - 45 mph range. French radar shows heavy rains from 99L are beginning to affect Southeast France and the island of Corsica. The Lion Buoy, located about 100 miles to the west of the center of 99L, recorded sustained winds of tropical storm force, 40 mph, at 00 UTC yesterday. Water temperatures at the buoy were 17°C (63°F), far below the 26°C threshold usually needed to sustain a tropical storm. The coldest waters I've seen a tropical storm form in were 22°C during Hurricane Epsilon of 2005. I doubt that NHC would name this system if they did have responsibility for the Mediterranean, due to the cold water temperatures.

"Rolf" is expected to move slowly northwards into the coast of South France by Wednesday night. Meteo France is predicting heavy rains of 30 - 40 mm/hr (1.2 - 1.6"/hr) will affect the coast Tuesday night through Wednesday, with sustained winds of 50 mph, gusting to 75 mph.


Figure 3. Hybrid subtropical storm of October 8, 1996, off the coast of Italy. According to Reale and Atlas (2001), the storm had characteristics similar to a hurricane, but formed over water of 21.5°C. "The maximum damage due to wind occurred over the Aeolian Islands, at 38.5°N, 15°E, to the northeast of Sicily: assistance for disaster relief was required. Unfortunately, no weather station data were available, but the media reported sheds, roofs and harbor devices destroyed, and houses and electric lines damaged, due to "extremely strong westerly wind." The perfect agreement between the observations at Ustica, the storm scale, the eye-like feature position and the damages over the Aeolian Island reasonably suggest that the hurricane-level intensity of 32 m/s (72 mph) was reached over the Aeolian Islands." A similar hybrid low affected Algeria on 9 - 10 November 2001. This storm produced upwards of 270 mm (10.6") of rain, winds of 33 m/s (74 mph), and killed 737 people near Algeirs, mostly from flooding and mud slides. Image credit: Dundee satellite receiving station.

According to research published by Gaertner et al. (2007), an increase in ocean temperatures of 3°C in the Mediterranean by the end of the century could lead to hurricanes forming there. Miguel Angel Gaertner of the University of Castilla-La Mancha in Toledo, Spain, ran 9 different climate models with resolutions of about 50 km and found that some (but not all) of the models simulated hurricanes in the Mediterranean in September by the end of the century, when ocean temperature could reach 30°C.

Though the Mediterranean may start seeing hurricanes by the end of the century, these storms should be rare and relatively short-lived for three reasons:

1) The Mediterranean is quite far north and is subject to strong wind shear from jet stream activity.

2) The waters are shallow, and have relatively low heat content. There is no deep warm water current like the Gulf Stream.

3) The Mediterranean has a lot of large islands and peninsulas poking into it, increasing the chances that a tropical storm would weaken when it encountered land.

References
Meteo France has an interesting animation of the predicted winds and temperatures over the next few days.

Gaertner, M. A., D. Jacob, V. Gil, M. Dominguez, E. Padorno, E. Sanchez, and M. Castro (2007), Tropical cyclones over the Mediterranean Sea in climate change simulations,, Geophys. Res. Lett., 34, L14711, doi:10.1029/2007GL029977.

Reale, O., and R. Atlas. 2001: Tropical Cyclone-Like Vortices in the Extratropics: Observational Evidence and Synoptic Analysis, Weather and Forecasting, 16, No. 1, pp. 7-34.


Figure 4. Radar reflectivity image from the Tipton, OK tornado of November 7, 2011, showing a classic hook echo.


Video 1. Reed Timmer video of the November 7, 2011 tornado in Tipton, OK. Here's another excellent video of the Tipton tornado and a tornado near Manitou, OK from Texas Storm Chasers. Storm chasing IS dangerous: one storm chaser had his vehicle overturned, but got into another vehicle and continued the chase.

Shaken and stirred: an earthquake and tornado for Oklahoma
It was a rare multi-natural hazard day for Oklahoma yesterday, as the state experienced both a tornado and an earthquake, six hours apart. The damaging magnitude 5.6 earthquake that shook the state Saturday night spawned a magnitude 4.7 aftershock at 8:46 pm CST yesterday, 44 miles east of Oklahoma City. And at 2:47 pm CST, a tornado touched down in Southwest Oklahoma near Tipton. The tornado destroyed an Oklahoma State University agricultural office, and damaged a hay barn at a dairy farm. No injuries were reported. The UK MailOnline has an interesting article showing the radar image from Saturday's quake, which captured a massive groups of birds and insects that took flight after the ground shook.

This afternoon, NOAA's Storm Prediction Center has placed Southeast Oklahoma, East Texas, Southeast Missouri, and most of Arkansas in its "Slight Risk" area for severe weather, thanks to a strong low pressure system moving across the Plains. During the late afternoon, severe thunderstorms with high winds and large hail and expected over the region, and we cannot rule out an isolated tornado.

Bering Sea superstorm targets Alaska
A massive blizzard the National Weather Service is calling one of the most severe Bering Sea storms on record is gathering strength today to the west of Alaska. The storm is expected to "bomb" to a central pressure of 945 - 950 mb Tuesday night, and to 940 mb on Wednesday. These pressures, characteristic of a Category 3 hurricane, will be strong enough to generate sustained winds of Category 1 hurricane force over the waters to the west of Alaska, with winds of 50 - 70 mph expected along portions of the coast. Nome, Alaska is expecting a storm surge of 8 - 10 feet. Waves of 15 - 25 feet with ice on top will batter the shores, causing severe damage to the coast.

Jeff Masters

Earthquake Severe Weather Winter Weather Hurricane

Updated: 07:18 PM GMT del 08 novembre 2011

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Subtropical storm brewing near Bermuda; earthquakes and tornadoes for Oklahoma

By: JeffMasters, 01:52 PM GMT del 07 novembre 2011

An extratropical low pressure system that moved off the coast of South Carolina over the weekend is camped out over the Atlantic about 400 miles southwest of Bermuda. Satellite loops reveal that this low (98L) has developed a respectable amount of heavy thunderstorm activity near its center, and in a curved band to the north. Bermuda radar shows weak rain bands from 98L rippling across the island, with the strongest rain showers well to the island's southwest. Sustained winds at the Bermuda airport reached 30 mph, gusting to 44 mph this morning. Sustained winds near tropical storm force were occurring this morning at buoy 41048, about 300 miles west of Bermuda. Wind at the buoy were 38 mph, gusting to 47 mph at 6:50 am EST. Strong upper-level winds out of the west are creating 35 - 45 knots of wind shear over 98L, limiting development. Ocean temperatures are near 26.5°C (80°F), which is right at the boundary of being warm enough to support tropical storm formation. Since 98L is getting its start as an extratropical storm, it has cold air at its core aloft, and is surrounded by a large amount of dry air to its south and west. This dry air and wind shear suggests that 98L will initially be Subtropical Storm Sean if it develops, and not Tropical Storm Sean.


Figure 1. Morning satellite image of 98L.

Forecast for 98L
98L will drift slowly west or northwest today and Tuesday. The latest SHIPS model forecast predicts wind shear will fall to 20 - 30 knots on Tuesday, which should allow for some increased organization of 98L. The computer models show little or no development of 98L, with none of our reliable models predicting 98L will become a hurricane. NHC gave 98L a 40% chance of developing into a subtropical storm by Wednesday in their 7 am EST Tropical Weather Outlook. I'd put these odds higher, at 50%. Since 98L is probably already generating sustained winds in excess of 39 mph, it will likely be named immediately if it gains enough organization, and skip being classified as a subtropical depression. Bermuda is the only land area that need concern itself with 98L, as a trough of low pressure is expected to absorb 98L and lift it quickly to the northeast on Thursday. The center of 98L should remain more than 200 miles away from Bermuda during the week, but heavy rain squalls from the storm are likely to affect the island at times between now and Thursday. The remnants of 98L will likely bring heavy rain to Nova Scotia, Canada on Thursday night or Friday morning.


Figure 2. Severe weather outlook for today from NOAA's Storm Prediction Center.

Earthquakes and tornadoes for Oklahoma
Oklahoma has a chance for a rare multi-natural hazard day: simultaneous earthquakes and tornadoes. The damaging magnitude 5.6 earthquake that shook the state Saturday night spawned magnitude 3.3 and 3.4 aftershocks last night, and there is the potential for more aftershocks today. This afternoon, NOAA's Storm Prediction Center has placed much of Oklahoma and Central Texas in its "Slight Risk" area for severe weather, thanks to a strong low pressure system moving across the Plains. During the late afternoon, severe thunderstorms with high winds, large hail, and a few tornadoes are likely over this region. If you're in Oklahoma late this afternoon and feel a deep rumbling, it could be an approaching tornado OR an earthquake aftershock!

Jeff Masters

Earthquake Hurricane

Updated: 02:10 AM GMT del 10 novembre 2011

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Fourteen U.S. billion-dollar weather disasters in 2011: a new record

By: JeffMasters, 12:12 PM GMT del 04 novembre 2011

It's time to add another billion-dollar weather disaster to the growing 2011 total of these costly disasters: the extraordinary early-season Northeast U.S. snowstorm of October 29, which dumped up to 32 inches of snow, brought winds gusts of 70 mph to the coast, and killed at least 22 people. Not since the infamous snow hurricane of 1804 have such prodigious amounts of October snow been recorded in New England and, to a lesser extent, in the mid-Atlantic states. Trees that had not yet lost their leaves suffered tremendous damage from the wet, heavy snow. Snapped branches and falling trees brought down numerous power lines, leaving at least 3 million people without electricity. The damage estimate in Connecticut alone is $3 billion, far more than the damage Hurricane Irene did to the state. Hundreds of thousands still remain without power a week after the storm, with full electricity not expected to be restored until Monday.


Figure 1. Wet, heavy snow from the October 29, 2011 snowstorm weighing down trees still sporting their fall leaves in Winchester, VA. Image credit: wunderphotographer MaddScientist98.

The October 29 snow storm brings the 2011 tally of U.S. billion-dollar weather disasters to fourteen, thoroughly smashing the previous record of nine such disasters, set in 2008. Between 1980 - 2010, the U.S. averaged 3.5 of these weather disasters per year. Through August, the National Climatic Data Center (NCDC) estimated that ten weather disasters costing at least $1 billion had hit the U.S., at total cost of up to $45 billion. However, the October 29 snow storm brings us up to eleven billion-dollar disasters, and a new disaster analysis done by global reinsurance company AON Benfield adds three more. Flood damage from the remnants of Tropical Storm Lee in the Northeast on September 8 is now estimated at more than $1 billion, and two outbreaks of severe thunderstorms and tornadoes--one in April and one in June--now have damage estimates exceeding $1 billion. A remarkable seven severe thunderstorm/tornado outbreaks did more than $1 billion each in damage in 2011, and an eighth outbreak July 10 - 14 came close, with damages of $900 million. In total, the fourteen billion-dollar disasters killed 675 people. Tornadoes, hurricanes, and floods in these fourteen disasters killed over 600 people, putting 2011 into fourth place since 1940 for most deaths by severe storms. Only 2005, with over 1,000 deaths caused by Katrina, 1969, with over 700 hurricane and flood-related deaths, and 1972, with 676 hurricane and flood-related deaths, were deadlier years for storms, according to NOAA. The fourteen billion-dollar weather disasters of 2011 caused $53 billion in damage, putting 2011 in fifth place for most damages from billion-dollar weather disasters. The top damage years, according to NCDC in adjusted 2011 dollars, were 2005 (the year of Hurricanes Katrina, Rita and Wilma), 2008 (Hurricane Ike), 1988 (Midwest drought), and 1980 (Midwest drought). With nearly two months remaining in 2011, the potential exists for more billion-dollar weather disasters this year. Our first opportunity comes Tuesday, when the NOAA Storm Prediction Center is forecasting the possibility of a severe weather outbreak centered over Arkansas and Missouri.


Video 1. Remarkable video of the tornado that hit Tuscaloosa, Alabama during the April 25 - 30, 2011 Super Outbreak. This tornado outbreak was the most expensive U.S. weather-related disaster of 2011, with damages estimated at $9 billion. Fast forward to minute four to see the worst of the storm.

Here are AON Benfield's estimates of the damages and NCDC's estimates of the death tolls from 2011's fourteen billion-dollar weather disasters (a clickable version of this table with information on each disaster is available on our severe weather resource page):



Have a great weekend, everyone, and I'll be back with a new post on Monday.

Angela Fritz is subbing for Ricky Rood this week, and has written an interesting post on the latest climate change controversy, the release of the new Berkeley Earth Surface Temperature (BEST) study by skeptic Dr. Richard Muller.

Jeff Masters

Winter Weather

Updated: 02:37 PM GMT del 04 novembre 2011

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Preliminary IPCC report predicts increased weather extremes

By: JeffMasters, 02:26 PM GMT del 03 novembre 2011

There is at least a 2-in-3 probability that climate extremes have already worsened because of human-caused releases of heat-trapping gases like carbon dioxide, and some types of extreme weather events will increase in the coming decades as huge cost, says a preliminary draft of an international climate report leaked to the Associated Press (AP) this week. The Nobel Prize-winning United Nations Intergovernmental Panel on Climate Change (IPCC) issues reports on the state of the scientific knowledge of climate change every six years, with the next full report due out in 2013. However, the IPCC is working on a special report detailing the evidence that extreme weather events may be increasing due to climate change, and how we might best prepare for the coming increase in these costly and dangerous events. The IPCC Special Report on Managing the Risks of Extreme Events and Disasters (SREX) is due to be released later this month, after a meeting in Uganda, where diplomats will recommend changes to the preliminary document leaked to AP. The IPCC requires that all countries agree unanimously on the content of the official reports, so the language of the leaked report may undergo considerable change. In the AP article, University of Victoria climate scientist Andrew Weaver, who was not among the authors, is quoted as saying that the report was written to be “so bland” that it may not matter to world leaders. With the diplomats free to make changes to the report, I think it is likely that the already bland SREX report will be further watered down. Despite all the objections one hears about the extreme and dire predictions of the IPCC, the science in these reports is actually very conservative and watered down, due to the requirement that the language must be approved by every country (including oil producing nations such as Saudi Arabia.) So, it should grab our attention that the preliminary draft of the SREX report predicts that some regions of the world might suffer extremes so severe as to leave them "increasingly marginal places to live", heat waves could peak at 5°F hotter by 2050 and 9°F hotter by 2100, and intense single-day rainstorms that happen only once every twenty years now will happen up to once every five years by 2100. I'll have more on the SREX report after its official release.

Jeff Masters

Climate Change

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November Atlantic hurricane outlook

By: JeffMasters, 02:35 PM GMT del 01 novembre 2011

Hurricane Rina is gone, and the tropical Atlantic is quiet, with no threat areas to discuss, and no models predicting development of a tropical depression during the coming seven days. So, are we all done for 2011? Or will this seventh-busiest hurricane season of all-time spawn a Tropical Storm Sean? Let's try and come up some answers. Since the active hurricane period we are in began in 1995, ten of the sixteen years (62%) have seen one or more Atlantic named storms form after November 1, for a total of fifteen late-season storms:

2009: Hurricane Ida on November 4
2008: Hurricane Paloma on November 6
2007: Tropical Storm Olga on December 11
2005: the "Greek" storms Gamma, Delta, Epsilon, and Zeta
2004: Tropical Storm Otto on November 29
2003: Odette and Peter in December
2001: Hurricane Noel on November 5 and Hurricane Olga on November 24
1999: Hurricane Lenny on November 14
1998: Hurricane Nicole on November 24
1996: Hurricane Marco on November 19

Only three of these storms (20%) caused loss of life: Hurricane Ida of 2009, which killed one boater on the Mississippi River; Tropical Storm Odette of 2007, whose floods killed eight people in the Dominican Republic; and Hurricane Lenny of 1999, which killed fifteen people in the Lesser Antilles. "Wrong-way Lenny" was both the deadliest and the strongest November hurricane on record (Category 4, 155 mph winds). There have been only seven major Category 3 or stronger hurricanes in the Atlantic after November 1. Part of the reason for the relatively low loss of life for November storms is that they tend to form from extratropical low pressure systems that get cut off from the jet stream and linger over the warm waters of the subtropical Atlantic. These type of systems typically get their start in the middle Atlantic, far from land, and end up recurving northeastwards out to sea. However, as I noted in the wake of last year's Hurricane Tomas last November in my blog post, Deadly late-season Atlantic hurricanes growing more frequent, It used to be that late-season hurricanes were a relative rarity--in the 140-year period from 1851 - 1990, only 30 hurricanes existed in the Atlantic on or after November 1, an average of one late-season hurricane every five years. Only four major Category 3 or stronger late-season hurricanes occurred in those 140 years, and only three Caribbean hurricanes. But in the past twenty years, late-season hurricanes have become 3.5 times more frequent--there have been fifteen late-season hurricanes, and five of those occurred in the Caribbean. Three of these were major hurricanes, and were the three strongest late-season hurricanes on record. Dr. Jim Kossin of the University of Wisconsin published a 2008 paper in Geophysical Research Letters titled, "Is the North Atlantic hurricane season getting longer?" He concluded that yes, there is an "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high". The recent increase in powerful and deadly November hurricanes would seem to support this conclusion.


Figure 1. The strongest hurricane on record in the Atlantic in November, Hurricane Lenny, takes aim at the Lesser Antilles on November 17, 1999. Image credit: NOAA.

Forecast for November 2011
The oceans are certainly warm enough to support continued development of tropical cyclones. Sea Surface Temperatures (SSTs) over a wide area of the tropical Atlantic are 0.5 - 1.0°C above average, and are well above the 26°C (79°F) threshold typically needed to support tropical storm formation (Figure 2.) However, wind shear is starting to rise over much of the tropical Atlantic as the jet stream moves farther south in its usual seasonal cycle. Wind shear over most of the Atlantic will be too high to support tropical storm formation over the coming two weeks, according to the latest run of the GFS model (Figure 3.) Only the southern Caribbean and a few transient pockets in the middle Atlantic east and southeast of Bermuda will have low enough wind shear to support tropical storm formation over the next two weeks. The African Monsoon is quiet this time of year, and we no longer have African waves coming off the coast of Africa that can act as the seeds for formation of a tropical storm in the Caribbean. If we do get a tropical storm, it will probably be to the northeast of the Lesser Antilles, far from land, in a region where an extratropical low pressure system gets cut off from the jet stream and lingers long enough over warm waters to acquire tropical characteristics and get a name. Both the GFS and ECMWF models are suggesting a system like this may take form 7 - 10 days from now. Taking all these factors into account, I predict we are all done this hurricane season with storms that will cause loss of life, but there is still a 70% chance that we will get one or more named storms in the middle Atlantic that will stay out to sea and not affect land.


Figure 2. Sea surface temperatures in the Atlantic on November 1, 2011. The black dotted line is the 26°C (79°F) isotherm, which marks the boundary where tropical storm formation can typically occur. A large portion of the Atlantic is still capable of supporting tropical storm formation.


Figure 3. Wind shear forecast for November 11, 2011, as predicted by the 2am EDT November 1, 2011 run of the GFS model. The model is predicting low wind shear of less than 4 m/s (about 8 knots, light red colors) in the southern Caribbean and southern Lesser Antilles Islands. Very high wind shear in excess of 44 m/s (85 knots, orange colors), associated with the jet stream, will protect regions north of the Caribbean.

I'll have a new post Wednesday or Thursday.

Jeff Masters

Hurricane

Updated: 02:38 PM GMT del 01 novembre 2011

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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