NOAA's forecast: a very active, possibly hyperactive Atlantic hurricane season
The National Oceanic and Atmospheric Administration (NOAA) issued its 2010 Atlantic hurricane season forecast today. NOAA forecasts a very active and possibly hyperactive season. They give an 85% chance of an above-normal season, a 10% chance of a near-normal season, and just a 5% chance of a below-normal season. NOAA predicts a 70% chance that there will be 14 - 23 named storms, 8 - 14 hurricanes, and 3 - 7 major hurricanes, with an Accumulated Cyclone Energy (ACE) in the 155% - 270% of normal range. If we take the midpoint of these numbers, NOAA is calling for 18.5 named storms, 11 hurricanes, 5 major hurricanes, and an ACE index 210% of normal. A season with an ACE index over 175% is considered "hyperactive." An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecasters note that in regards to the oil spill in the Gulf of Mexico,
"Historically, all above normal seasons have produced at least one named storm in the Gulf of Mexico, and 95% of those seasons have at least two named storms in the Gulf. Most of this activity (80%) occurs during August-October. However, 50% of above normal seasons have had at least one named storm in the region during June-July."
The forecasters cited the following main factors that will influence the coming season:
1) Expected above-average SSTs in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa. SSTs in the MDR are currently at record levels, and the forecasters note that several climate models are predicting record or near-record SSTs during the peak portion of hurricane season (August - October.) "Two other instances of very warm SSTs have been observed in the MDR during February-April (1958 and 1969). In both years, the SST anomaly subsequently decreased by roughly 50% during the summer months. For 2010, although the record SST departures may well decrease somewhat, we still expect a continuation of above average SSTs throughout the Atlantic hurricane season. "
2) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO). "During 1995-2009, some key aspects of the tropical multi-decadal signal within the MDR have included warmer than average SSTs, reduced vertical wind shear and weaker easterly trade winds, below-average sea-level pressure, and a configuration of the African easterly jet that is more conducive to hurricane development from tropical waves moving off the African coast. Many of these atmospheric features typically become evident during late April and May, as the atmosphere across the tropical Atlantic and Africa begins to transition into its summertime monsoon state."
3) There will either be La Niña or neutral conditions in the Equatorial Eastern Pacific. El Niño is gone, and it's demise will likely act to decrease wind shear over the tropical Atlantic, allowing more hurricanes to form. "La Niña contributes to reduced vertical wind shear over the western tropical Atlantic which, when combined with conditions associated with the ongoing high activity era and warm Atlantic SSTs, increases the probability of an exceptionally active Atlantic hurricane season (Bell and Chelliah 2006). NOAA's high-resolution CFS model indicates the development of La Niña-like circulation and precipitation anomalies during July."
How accurate are the NOAA seasonal hurricane forecasts?
A talk presented by NHC's Eric Blake at the 2010 29th Annual AMS Conference on Hurricanes and Tropical Meteorology studied the accuracy of NOAA's late May seasonal Atlantic hurricane forecasts, using the mid-point of the range given for the number of named storms, hurricanes, intense hurricanes, and ACE index. Over the past twelve years, a forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Using another way to measure skill, the Mean Squared Error, May NOAA forecasts for named storms, hurricanes, and intense hurricanes had a skill of between 5% and 21% over a climatology forecast (Figure 2). Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.
Figure 1. Mean absolute error for the May and August NOAA seasonal hurricane forecasts (1999 - 2009 for May, 1998 - 2009 for August), and for forecasts made using climatology from the past five years. A forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.
How do NOAA's seasonal hurricane forecasts compare to CSU and TSR?
Two other major seasonal hurricane forecasts will be released next week. On June 2, Phil Klotzbach and Bill Gray of Colorado State University (CSU) issue their forecast, and the British firm Tropical Storm Risk (TSR) will issue their outlook on June 4. A three-way comparison of the forecast accuracy of the three groups' forecast (Figure 2) reveals that all three organizations enjoy some success at making accurate seasonal forecasts, with NOAA and CSU making the best late May/early June forecasts overall. While the skill of these forecasts is low, they are useful for businesses such as the insurance industry.
Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August). using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.
Central American disturbance
The Atlantic is currently quiet, with the non-tropical storm (90L) that we were watching now no longer a concern. There is an area of disturbed weather (90E) just off the Pacific coast of Mexico that will be a major concern for southern Mexico and much of Central America over the next 3 - 4 days. The disturbance will bring heavy rains to Central America during the remainder of the week, potentially bringing serious flooding rains to portions of Mexico, Guatemala, El Salvador, Honduras, and Nicaragua. NHC is giving the disturbance a high (>60% chance) of the disturbance developing into a tropical depression by Saturday. There is the potential for disturbed weather accompanying the disturbance--or the disturbance itself--to push into the Western Caribbean early next week and pose a threat to develop into a tropical depression. While there is high wind shear over the northern Caribbean, shear may be low enough to allow development should the disturbance stay in the southern reaches of the Caribbean. None of the models are currently calling for this to happen, and I think the threat is low. Any storm that develops in the Caribbean in the coming week would get steered to the northeast and will not pose a threat to the Gulf of Mexico. Wunderbloggers Weather456 and StormW have more on the tropics.
Figure 3. Visible satellite image of the Central American disturbance 90E this morning.
Oil threat for the coast of Louisiana to decrease this weekend
Light winds from the north or west are expected to prevail across the northern Gulf of Mexico through Friday, resulting in a lessened threat of oiling to the Louisiana shoreline, according to the latest trajectory forecasts from NOAA. However, the latest runs of the GFS model indicate a return to onshore winds out of the southwest for most of next week, which will likely bring oil back towards shore. At greatest risk will be the coast of Louisiana, and there will be heightened risk to Mississippi, Alabama, and the Florida Panhandle. I'll a have a more in-depth discussion of the oil spill forecast in Friday's blog.
Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami
Join the Hurricane Haven with Dr. Jeff Masters: a new Internet radio show
Beginning next week, I'll be experimenting with a live 1-hour Internet radio show called "Hurricane Haven." The show will be aired at 4pm EDT on Tuesdays, with the first show June 1. Listeners will be able to call in and ask questions. Some topics I'll cover on the first show:
1) What's going on in the tropics right now
2) Preview of the coming hurricane season
3) How a hurricane might affect the oil spill
4) How the oil spill might affect a hurricane
5) New advancements in hurricane science presented at this month's AMS Conference on Hurricanes and Tropical Meteorology
6) Haiti's vulnerability to a hurricane this season
I hope you can tune in to the broadcast, which will be at http://www.wunderground.com/wxradio/wubroadcast.h tml. If not, the show will be recorded and stored as a podcast.
Jeff Masters
Reader Comments
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With all the dry air above 500mb it's not actually that big of a deal for 90E, but that's a good observation.
Crickets....big uns
Crickets....big uns
Crickets....big uns
2245 UTC
How come everyone else had a poetic mother, but me? All mine said was "put that back on the shelf or you won't be able to sit without wincing for the next month like last time!"
Actually now that I think about it, 90E may be causing the upper-level dry air. Acapulco is on the northwest fringes of the disturbance, and the dry air in the high levels of the atmosphere could signify the air that is outflowing away from the top of the storm starting to sink at the storm's edges. Sinking dries the air.
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 PM PDT THU MAY 27 2010
FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..
SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE BROAD AREA OF LOW
PRESSURE CENTERED A COUPLE OF HUNDRED MILES SOUTH OF THE GULF OF
TEHUANTEPEC HAVE BECOME LESS CONCENTRATED THIS AFTERNOON.
ENVIRONMENTAL CONDITIONS...HOWEVER...STILL APPEAR FAVORABLE FOR
GRADUAL DEVELOPMENT...AND A TROPICAL DEPRESSION COULD FORM DURING
THE NEXT DAY OR SO. THE SYSTEM IS EXPECTED TO MOVE LITTLE OR
DRIFT SLOWLY NORTHEASTWARD OVER THE NEXT COUPLE OF DAYS...AND HAS
THE POTENTIAL TO PRODUCE LOCALLY HEAVY RAINS...FLOODING...AND MUD
SLIDES OVER PORTIONS OF CENTRAL AMERICA...ESPECIALLY OVER EL
SALVADOR...SOUTHERN HONDURAS...AND COASTAL GUATEMALA. THERE IS A
HIGH CHANCE...60 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER BROWN/ROBERTS
Ahhh,..now were making progress,...go on please
Less consolidate than previous
Just goes to show the model data is not always trustworthy and those cyclone phase diagrams can be wrong.
Hershey Box? I thought that was in Pennsylvania. Oh wait...I thought you meant the Hershey BAR.
Go back a few pages and read Tampa's post. I do not know why he is seeking to banger W456. 90L has come and gone.
True
contradicts the TWD that says moderate chance
Any diagram can be wrong lol
lol
That is true as well lol. But there are more direct observations we can look at besides model-estimated data, which is mostly what those phase diagrams are made of.
Fire away!
Drama, and its only May
Me too.
That was totally uncalled for. You knew your motives when pointed out and ask W456 that question. He is 10 times better than you ever will be.
Can you imagine this blog with 23 named storms? I've got to stay out of the arguing in 2010.
Imagine having multiple storms at once with everyone's opinion. Going to be a rough season...
You're just asking for a fight. That was disrespectful. Over the line, dude, over the line.
I don't even want to think about when it really gets crazy.
Gone to watch the (bad) news on tv. Later.
Yikes!
Quoting Weather456:
Excuse me?
90L did everything I expected it to do. It was initiated by an upper trough, move towards the Carolinas and became vertically stacked. Most, if not all the aspects of what I forecasted with 90L verified, even down to it becoming subtropical as per the Dvorak numbers which used tropical cloud patterns to give 90L a T# of 1.0. So before you begin to question what I said, go and read my blog entries on 90L.
He said he wasn't badgering you and you still took it to heart. You did not nailed it in it being subtropical; it is and always has been nontropical. Admit the mistake and move on.
Exactly Drak.....i just asked a simple question....as to what happened that it did not strengthen as he was suggesting.....hey everyone makes forecast errors and i didn't even say he was in Error of his forecast...UNREAL!
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