Little change to 90L; flow of oil southwards towards Loop Current shuts off
An extratropical low pressure system a few hundred miles northeast of the Bahamas (90L), has changed little over the past day. (For those of you who were wondering, a discussion of what an "Invest" is can be found in the Tropical Cyclone FAQ). This low has the potential to develop into the season's first depression or subtropical storm, and could be a threat to the Southeast U.S. coast by Tuesday or Wednesday. The SHIPS model predicts that shear will be in the high 30 - 40 knot range through Tuesday, though. The high shear combined with the large amount of dry air to 90L's west seen on water vapor satellite loops will greatly hamper transition of this system to a subtropical storm. This system is expected to move slowly north and then northwestward towards the Southeast U.S. coast over the next three days, and could bring 20 - 30 mph winds and heavy rain to the coast of North Carolina by Tuesday night. Most of the models indicate that Wednesday will be when 90L gets closest to the coast, with a position just off the North or South Carolina coast. All of the major models currently indicate that 90L will not make landfall, but will move slowly northeastward out to sea late next week as a trough of low pressure moving across the Eastern U.S. picks up the storm. While the storm will initially form in a region of high wind shear and be entirely extratropical, it will move into a region of lower wind shear in a gap between the polar jet stream to the north and the subtropical jet stream to its south by Wednesday. At that time, the low will be positioned near the warm waters of the Gulf Stream, and will have the opportunity to develop a shallow warm core and transition to a subtropical storm. The counter-clockwise flow of air around this low will probably lead to offshore winds over the oil spill region Tuesday through Wednesday, keeping oil away from the coasts of Alabama and the Florida Panhandle, but pushing oil southwards towards the Loop Current. Wunderbloggers Weather456 and StormW have more detailed discussions of the potential development of 90L.
Figure 1. Visible satellite image of 90L this afternoon.
Heavy rainfall threat for Haiti diminishes
Moisture is expected to increase across most of the Caribbean next week, leading to seasonally heavy rains across much of the region. A concentrated tropical disturbance capable of bringing dangerous flooding rains to Haiti is no longer being indicated, but the normal heavy rains that we can expect this time of year will likely begin affecting the island over the next several weeks.
Flow of oil southward towards the Loop Current shuts off
Light southeast to east winds are expected to blow over the northern Gulf of Mexico today through Monday, resulting in potential oiling of Louisiana shorelines from the mouth of the Mississippi River westward 150 miles, according to the latest trajectory forecasts from NOAA. These winds shut off the flow of oil southwards towards the Loop Current, as seen in the latest SAR satellite imagery (Figure 2). However, winds will shift to offshore out of the north or northeast Tuesday and Wednesday, due to counter-clockwise flow of air around the approaching 90L storm. This wind direction change should give some relief to the hard-hit Louisiana coast. If 90L becomes strong and lingers off the Southeast U.S. coast for several days, a significant amount of oil could get pumped into the Loop Current late next week.
Figure 2. Synthetic Aperture Radar (SAR) image of the oil spill taken at 8:53am EDT May 22, 2010, by the Canadian Radarsat-1 satellite, operated by MDA GeospatialServices of Richmond, Canada. The plume of oil being drawn south towards the Loop Current has been cut off. Image credit: Center for Southeastern Tropical Advanced Remote Sensing, University of Miami Rosenstiel School of Marine and Atmospheric Science. SAR images have a resolution of 8 - 50 meters, and can be taken through clouds and precipitation.
Oil threat to the Keys uncertain
Satellite imagery from today's pass of NASA's Terra satellite and the European Envisat satellite were inconclusive as to the presence of oil in the Loop Current. It is likely that the oil has dispersed significantly over the 500-mile course it has taken from the site of the Deepwater Horizon blowout. I expect some oil is close to completing the full loop of the Loop Current and is now headed east towards the Keys, as depicted in the "Uncertainty" area in the latest NOAA 72-hour offshore trajectory forecast. If this estimate is correct, the Keys could see oil as early as Wednesday. However, this is not a sure thing. As I discussed in my post Wednesday, the Loop Current is very unstable right now, and is ready to cut off into a giant clockwise-rotating eddy, an event that occurs every 6 - 11 months. This event could occur today or tomorrow, in which case the ribbon of southwestward-moving oil would turn due west and then north, eventually winding up back near the site of the Deepwater Horizon blowout. Roffer's Ocean Fishing Forecast Service has a nice discussion on the possibility of the Loop Current cutting off into a Loop Current Eddy, and they note in today's discussion that there appears to be a developing eastward flow of water directly from the Yucatan Peninsula to the Florida Keys. Keep in mind, though, that during the first month that a Loop Current Eddy forms, it exchanges a considerable amount of water with the Loop Current. Even if a Loop Current Eddy forms today, I still expect we will see some oil make the turn eastward and flow past the Florida Keys by Wednesday. My guess is that the oil will be too thin and scattered to cause significant problems in the Keys, but there is great uncertainty on this.
Oil spill resources
My post Wednesday with answers to some of the common questions I get about the 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
I'll be back with a new post Monday morning.
Jeff Masters
Reader Comments
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I wasnt comparing the two at all, it was just a side note that Andrew at one point had no LLC
I totally understand Levi's explantion but I have to respectfully disagree with part of yours. Mid Lat or extra Trop cyclones can have vertically stacked Lows. That is why I said the maturing stage. In the maturing and esspecially int he disipating stage, the lows typically are stacked. yes the first two stages the ULL is to the NW.
I do buy the fact that an ULL will relax the shear and allow a system over water to build a warm care and turn subtropical and possibly Trop.
Tropical, no, but subtropical cyclones often have cold air aloft associated with an upper low. It is this very cold pocket aloft that increases the lapse rate and allows subtropical cyclones to survive over SSTs as low as 23C. Sometimes, over high enough SSTs, a subtropical low can warm the air column enough to disperse the upper low and cold pocket and become a fully tropical system with a deep warm-core structure.
ULLs are great babysitters for hybrid lows trying to become tropical.
and what to drink?
Hard to get to be a Cat 5 without a LLC,,but the Double eyewall was a Well documented event by radar with Andrew.
And Impressive as one can get ,,for that size Vortex.
moving WNW/NW, convection is beginning to develop, but nothing drastic..
new gfs
I don't normally track in the mid-latitudes so you maybe correct but from what I have seen, one of the general rule of thumbs in separating extra-tropical cyclones from hybrid from Tcs is the vertical profile I stated.
And find some periods too.
LOL
i make sure it takes out the dog
What you were describing is correct for developing mid-latitude cyclones, but after occlusion the surface low often becomes vertically stacked with the upper low. This is one of the reasons why an occluded low starts to fill, because there is no longer upper divergence over the surface low.
Just set it,..and forget it
Well a mid lat cyclone is also called an extra trop cyclone and when it fully matures the vertical profile is a closed ULL at at least 500mb if not higher. This is when the front and entire system actually hits its peak before it starts to fill. YOu know that when you are forecasting and see the Low maturing that your weather will get worse however if you are far enough away downstream then it might fall apart before it ever gets to you.
I really wonder if the models are treating this as extratropical. Seems that timing is right. ULL moves over head and most models weaken 90L around the time you would expect it an extratropical cyclone to fill.
if it stalls then it will move back to the South east when the high behind the trough/Front begins to build in..
Yes! A system that is already a Warm Core system can Vent better and Breathe from an ULL directly aloft....but, it won't enhance the chances of a Non Tropical system to become tropical except for a very long process of warming and this system does not have a long time to sit and warm. JMHO
Nite all. Says your prayers and don't let the bed bugs bite. (If you have bed bugs... you have problems!) LOL
A fully tropical transition isn't highly likely, but a subtropical storm can develop with an upper low still on top.
OK i understand that.
HaboobsRsweet,
So then why compare this vertically stacked 90L with an occluding cyclone's vertically stacked upper low? We all know no occlusion is taking place.
Plaquemines officials consider paying for own oil containment effort
Oil is pushing into more and more stretches of coastal marsh in Plaquemines Parish, with stalks of cane now appearing to wilt from an onslaught of oil.
lol lol
Yes Levi you are correct....Don't get me wrong i am not questioniong weather we might get a SubTrop. of XtraTrop. system to play with, but i see no way we will ever have a Fully Tropical system to ever see. Tropical systems don't live in Cold waters well when trying to become Tropical.
Humor attracts the worms..
LOL.
Pfffttt
no, I just found it funny lol
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