90L heads for North Carolina, drenches Bermuda; oil spill changing little

By: Dr. Jeff Masters , 2:54 PM GMT on May 24, 2010

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An extratropical low pressure system (90L) between the Bahamas and Bermuda is moving north-northwest towards North Carolina and is close to tropical storm strength. Last night's ASCAT pass saw a large area of 35 mph winds to the north and east of the center, and buoy 41048 to northeast of 90L's center was seeing sustained ENE winds of 36 mph, gusting to 43 mph this morning. Bermuda is seeing some heavy weather from this storm, with winds blowing at 35 mph on the west end of the island, and the Bermuda radar showing an area of moderate to heavy rain moving over the island. Seas are running 5 - 10 feet in the outer waters of Bermuda today, and are expected to increase to 10 - 14 feet tonight before diminishing on Tuesday.


Figure 1. Visible satellite image of 90L this morning.

Strong upper-levels winds out of the west are creating about 25 knots of wind shear over 90L, but the shear has been gradually decreasing over the past day. Visible satellite loops show that 90L does not have a well-defined surface circulation. The main thunderstorm activity is in a large curved band to the north and northeast of the center. This band is several hundred miles removed from the center, which is characteristic of subtropical storms. I expect that 90L will continue to grow more subtropical in nature today through Wednesday as the shear continues to fall. Sea surface temperatures are near 25°C today and will fall to 23 - 24°C on Tuesday. This is warm enough to support a subtropical storm, but probably not a tropical storm. On Wednesday, 90L will be nearing the warm waters of the Gulf Stream, and SSTs will warm again, to the 24 - 25°C range. This is still pretty cool for a tropical storm, and I expect 90L will never become fully tropical. To understand the difference between a tropical and subtropical storm and why we care, see my subtropical storm tutorial.

The SHIPS model predicts that shear will fall to the medium 10 - 20 knot range by Tuesday. A large amount of dry air to 90L's southwest associated with the upper-level trough of low pressure on top of the storm, as seen on water vapor satellite loops , will hamper transition of 90L to a subtropical or tropical storm. The system will move slowly towards the Southeast U.S. coast over the next two days, making its closest approach to the coast on Wednesday, when most of the models indicate the center will be 200 - 400 miles southeast of Cape Hatteras, North Carolina. All of the major models currently predict that 90L will not make landfall, but will move slowly eastward out to sea on Thursday, when a trough of low pressure moving across the Eastern U.S. picks up the storm. There presently isn't much to be concerned with about this storm, as it appears that it will remain offshore and will become, at worst, a 40 - 50 mph subtropical storm. The National Hurricane Center (NHC) is giving 90L a medium (30% chance) of developing into a depression or tropical/subtropical storm. Wunderbloggers Weather456 and StormW have more on 90L.

Western Caribbean disturbance
A small region of disturbed weather has developed in the Western Caribbean, off the east coast of Nicaragua. Moisture is expected to increase across in this area in the coming days, and by Saturday, the GFS and NOGAPS models predict that shear will drop low enough to permit the possible development of a strong tropical disturbance or tropical depression. This storm would then move northeastward over eastern Cuba early next week. The other models keep the shear high in the Caribbean all week, and do not show anything developing. Thus, the Western Caribbean bears watching later this week, but the conditions appear marginal for development.

Moderate risk of severe weather today in northern Plains
The Storm Prediction Center has placed western Nebraska and portions of South and North Dakota under their "Moderate" risk for severe weather today. They warn that "a couple of strong and possibly long-track tornadoes appear possible given the forecast scenario." Keep an eye on the activity today with our Severe Weather Page.

Major oil threat continues for the coast of Louisiana
Light winds are expected to prevail across the northern Gulf of Mexico all week, resulting in continued oiling threats to the Louisiana shoreline from the mouth of the Mississippi River westward 150 miles, according to the latest trajectory forecasts from NOAA. There is no longer a flow of oil moving southwards towards the Loop Current, and the oil that did move southwards last week was mostly entrained into a counter-clockwise rotating eddy attached to the northern boundary of the Loop Current. Synthetic Aperture Radar (SAR) imagery over the weekend showed that most of this oil has dispersed, and very little of this oil is now visible from space (Figure 2.) Imagery from NASA's MODIS instrument and from NOAA aircraft did not show any oil in the Loop Current headed towards the Florida Keys over the weekend, so that is good news. NOAA comments that there may be some "scattered tar balls" in the Loop Current headed towards the Florida Keys. I expect these scattered tar balls have completed the full loop of the Loop Current and are now headed east towards the Keys, and will pass the Dry Tortugas and Key West sometime Wednesday - Saturday. My guess is that the oil and its accompanying plume of toxic dispersants will be too thin and scattered to cause significant problems in the Keys.


Figure 2. Synthetic Aperture Radar (SAR) image of the oil spill taken at 11:41am EDT Saturday May 22, 2010, by the European Envisat-1 satellite. Only scattered patches of oil are evident in the counter-clockwise rotating eddy on the northern boundary of the Loop Current. A small amount of oil appears to be in the Loop Current, and is moving southward. 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.

Future threats to the Keys
Mostly offshore winds are expected this week over the northern Gulf of Mexico, thanks to the approach of the 90L storm along the Southeast U.S. coast. It is uncertain if these winds will be strong enough to push oil southward into the Loop Current, though at least one ocean trajectory model does show this occurring. 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. At least one ocean model (the Global HYCOM model from the HYCOM consortium) is predicting that such an eddy will form this week. In the event a Loop Current Eddy does break off, it would create a rotating ring of water 250 miles in diameter to the south of the oil spill. Oil moving southwards would tend to enter the giant eddy and circulate around it, not threatening any land areas. Roffer's Ocean Fishing Forecast Service has a nice discussion on the possibility of the Loop Current cutting off into a Loop Current Eddy. 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. Thus we can expect that a portion of any oil moving southwards into a Loop Current Eddy will find its way into the Loop Current and move past the Florida Keys.

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 Tuesday morning.

Jeff Masters

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Im telling you shear is not going to drop. I can assure everyone its gonna stay strong most of the season discouraging a lot of activity. this year may very well be no different than last year.I foresee very little action.
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1133. IKE
00Z UKMET


00Z CMC


6Z NOGAPS
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1132. IKE
90L....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Most of the reliable models show this in the NW Caribbean

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Hmm. Point taken, I suppose.

Anyhow, gonna try and get a few hours of sleep. Got some things to do in the AM.

See ya around, Storm!
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Quoting StormW:
Enter, La Nina



I wonder when the shear is going to start dropping in response?
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Quoting IKE:
Looks like the 00Z ECMWF continues to diminish the significance of 90L.

After looking at a satellite on it, I see why. ECMWF also shows a system in the east-PAC but kills it after landfall, with nothing on the Caribbean side.

Don't see much in the western Caribbean on the GFS or CMC,.


There is at least a broad and disorganized area of low pressure around days five and six.
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1123. guygee
BP Oil Leak - Has the casing finally eroded away?

Some bloggers monitoring the live feed of the leak have detected some possible major changes in the flow of oil around the riser, with gas venting now from the seafloor. Waiting on some verification, but check it out for yourself...it looks bad:

Major Change Down Below...


Off to try and get a couple hours of sleep...
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Looking at the latest IR satellite this is a complete utter mess. It can't look much worse than this. It's peak time is supposed to be later this evening. It's way too broad to tighten up now. At least the carolina coast will get some needed rain showers today.
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1121. guygee
Quoting MahFL:
Hello Guy, I see a new center at 73/30. Also some green on the IR is now showing, which means thunderstorms are not getting sheared as much.
I agree the shear is relaxing, so I haven't given up on 90L yet. Still weird looking in the vicinity of the ULL and dry air, but I think the environment is becoming more favorable.

Already north of my latitude, so even if it drifts left of forecast best I can hope for is some onshore convergence bands, then maybe some strong storms popping the cap as the upper flow backs to the NW.
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1120. MahFL
Hello Guy, I see a new center at 73/30. Also some green on the IR is now showing, which means thunderstorms are not getting sheared as much.
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1119. guygee
Good morning all.
Working hard in the yard all day yesterday, then accidentally fell asleep at 8:30 PM, then up since 2:00 this morning. I hate that when it happens.

Watching 90L IR2 loops...broad low perhaps a little more WNW than previous forecasts? Getting some wraparound moisture now.

STS's can be strange beasts...perhaps this will stay extratropical, but I have to admit I am wishcasting for some drenching rains on the parched Space Coast. At least a few convergence bands working in from the NNE attm.
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1118. IKE
Looks like the 00Z ECMWF continues to diminish the significance of 90L.

After looking at a satellite on it, I see why. ECMWF also shows a system in the east-PAC but kills it after landfall, with nothing on the Caribbean side.

Don't see much in the western Caribbean on the GFS or CMC.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting Weather456:
I am becoming more confident of an Alma-Arthur scenario.

Morning all


Good morning.

As far as the Alma/Arthur scenario goes, I agree that it's possible, but I would like to see how the steering pattern evolves over the coming days, as well as how the current Pacific disturbance organizes itself over the next several days. As I said earlier, it has some moderate easterly shear and some ITCZ convection to contend with, the latter of which severely hampered intensification of Carlos last year.

Still, there are several models, including the CMC, GFS, and ECMWF, forecasting tropical cyclogenesis in this area in just three to four days, and if that's the case, there may be enough of a remnant mid-level circulation to aid in the birth of a tropical cyclone in the western Caribbean by late this weekend or early next week.

We'll see. Like I said though, I'd rather keep watch on the steering forecasts over the next several days.
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1116. MahFL
New center 74/29 ?
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Quoting Weather456:
I am becoming more confident of an Alma-Arthur scenario.

Morning all


Night all.. LOL, its 3 AM here. Take over 456.
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1114. MahFL
Morning 456, I am pulling an extra half shift. Some showers heading to me from the Atlantic, I am just SW of Jax.
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I am becoming more confident of an Alma-Arthur scenario.

Morning all
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1112. xcool


new

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1064 CapeCoralStorm "I'm using a PC with Firefox. Looks like mym options are scroll down to the bottom after posting, or learn to read/keep up bottom to top."

Nope. When you change reading preferences (order or filter), you have refresh, then go to a new off-site page, then reenter (and not use "Go back one page") through the TropicalStorm frontpage before the change will "catch", goes into effect.
At least that was the way it worked for me.
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1110. xcool
i'm back.
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0z GFS develops the current area of disturbed weather in the Gulf of Tehauntepec into Tropical Storm Agatha at 72 hours:



However, it appears that this system will have some competing influences to contend with; namely, moderate easterly shear as well as a large area of precipitation to the west, associated with the ITCZ. Monsoon-type systems like this one typically take awhile to organize, so we'll see what happens.

I believe that this is the very same system that the models foresee could become a tropical depression across the western Caribbean by this weekend or early next week.
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1107. Levi32
Goodnight all.
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1106. xcool



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1105. Levi32
Quoting StSimonsIslandGAGuy:
I see a low pressure swirl around 28.3 N 70.1 W, and no convection within 200 miles. I don't see any signs of rapid organization happening soon.

However, we may get a little rain here after 2 am.



There's also a new one at 30N, 71.9W. It will take a while to try to consolidate this thing, but it has 2-3 days, so I would not take any eyes off of it. Convection will finally have the chance to try to develop around the center instead of away from it.
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1103. xcool
winter123 yeah...
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Quoting xcool:
winter123 I really don't know.

Guess we play the waiting game.. I'll be back tomrorow
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1101. xcool
winter123 I really don't know.
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Quoting xcool:





So what, is our Carribean storm actually gonna bomb into a huge rainmaker for the pacific central america coast instead?
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1099. xcool



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Quoting Levi32:


Only problem is all the countless lows that have come out and died have resulted in the entire circulation being very enlarged and broad.


yea true
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1097. Levi32
Quoting Hurricanes101:


I wonder though, I see what Winter is saying about another low spinning up at 30N 72W close to that convection

This low further south dying may actually help 90L more than hurt it


Only problem is all the countless lows that have come out and died have resulted in the entire circulation being very enlarged and broad.
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1096. xcool
Hurricanes101 yeah lmao.
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Quoting Skyepony:
3hrs later on ASCAT (and about 3 hrs ago)...if you can't stand to watch one die turn away..


I wonder though, I see what Winter is saying about another low spinning up at 30N 72W close to that convection

This low further south dying may actually help 90L more than hurt it
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1094. Levi32
Quoting Skyepony:
Levi~ Congrats:)

Evening Windsat


Thanks :)
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new surface map (00Z)



Member Since: June 13, 2009 Posts: 2 Comments: 10852
Quoting xcool:
yeah thanks .opps my bad


actually looking at the loops it should be over the water lol
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1091. Skyepony (Mod)
3hrs later on ASCAT (and about 3 hrs ago)...if you can't stand to watch one be slaughtered by shear & dry air turn away..
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1090. xcool
yeah thanks .opps my bad
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new main circulation desperately trying to take over at 30N 72W, just east of the new blowup. You can't see it on the floater but you can see it here, especially in motion and speed up the loop to max speed. I still think it has a 50-75% chance. Dunno if I'll post again goodnight if not and we shall see tomorrow.

Link
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Quoting xcool:



1003 low in epac


Actually that is over Central America, not in the EPAC
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1087. xcool



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Quoting Skyepony:
Levi~ Congrats:)

Evening Windsat


I think that may be the best defined any circulation has been since 90L got going lol
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1085. Skyepony (Mod)
Levi~ Congrats:)

Evening Windsat
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It is currently 12:38 AM in Florida; I am very sleepy. Good night!
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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.