TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 2:38 PM GMT on August 13, 2009

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Tropical Depression Two is near death, but is still worth watching. The dry, Saharan air to the north and west of the depression, combined with moderately high levels of wind shear of 15 - 20 knots, have almost completely destroyed all of TD 2's heavy thunderstorms. Satellite loops of the storm show a well-formed circulation, but almost no heavy thunderstorm activity.

Wind shear over TD 2 is expected to remain in the modereate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C three days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to to TD 2's north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that TD 2 will not be able to intensify quickly, and some of the models indicate the TD 2 may get destroyed in the next day or two. However, several models still predict TD 2 will become a tropical storm. The HWRF model predicts TD 2 will become a hurricane five days from now, but this seems unlikely given the dry air and relatively high wind shear affecting the storm.


Figure 1. Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

African tropical wave 90L
A strong tropical wave with a large circulation and plenty of heavy thunderstorm activity is a few hundred miles south of the Cape Verdes Islands, off the coast of Africa. NHC dubbed this disturbance 90L this morning. This morning's QuikSCAT pass shows that 90L has a very large circulation, and top winds of about 30 mph. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are in two major bands, to the north and to the south of the center. There is no heavy thunderstorm activity near the center yet, and this would have to happen before 90L can be named Tropical Depression Three. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two has been. Wind shear is about 20 knots over 90L, and is forecast to remain in the moderate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days, which are high enough above the 26°C threshold for tropical cyclone formation to allow some slow development to occur. The GFS and ECMWF models continue to predict the development of this wave, though they are now less aggressive about intensifying it than they were in earlier runs. The consensus among the reliable HWRF, GFDL, GFS, and ECMWF models is to bring 90L to point near or just north of the northernmost Lesser Antilles Islands 6 - 8 days from now. The storm could be at hurricane strength by then, as forecast by the SHIPS intensity model.

I'll have an update Friday morning.

Jeff Masters

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Quoting NOLABean:
What are GOM temps like right now?


I got over 92 degrees in the boat on Saturday 30 miles south of fort morgan.
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In watching the satellite loop for Tropical Depression 2 this afternoon, it seems like shear is not having as great an impact as it did yesterday. Would say the only problem it has now continues to be the dry stable airmass that the system exists in. If it can just tap into the ITCZ, it would have a decent chance.
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Code Red...Second One of the Season...Here you go WS. LOL
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Quoting Drakoen:
Looking at the GFS it could be a close call whether the system impacts Florida than I originally thought. The GFS depicts a deep layered ridge south of the base on the deep layered longwave trough. The shortwave will have a ridge behind it. So steering gets a little complex.
hey drak according to the models when next week does it make its closest approach to south florida or florida
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Quoting largeeyes:
TD2's convection has now gotten narrowed as it is being blown from the COC. Small patch still on the west side, but the majority of it is in danger of seperating completely.


Indeed. Easterly shear is still quite strong even with the slight increase in forward motion that you mentioned earlier... The GFS shows the easterly shear becoming southerly shear nearly as strong for the day tomorrow.

Tough road ahead for TD2!
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Quoting szqrn1:


LOL that's funny!
On serious note so I don't get blocked for playing... models show this in GOM at all?


The long range models, highly skeptical, show it either re-curving before or right at the east coast. So an answer to your question right now would be no. Being so far out though you'd have a better chance of winning the Power Ball than answering that with accuracy. Speaking of power ball 213million {drool}
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730. Skyepony (Mod)
Still a bit leary about the wave north of Hispanolia Was hoping the N end & Mid level vorticy there would run over the islands slowing it down. Looks like it's going a little north & gaining convection quick..
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Quoting btwntx08:
posts 661 and 662 ur votes not count i said only 1 vote cause it was a tie and someone already did so thanks anyways

aww sorry guys, you miss out on the trip to disney the other winners ot
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Quoting TerraNova:
Wow...

Holy cow, what's new, it's the HWRF, it always does this, but if that would be the case i would be evacuating for the first time ever.
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Quoting NOLABean:
What are GOM temps like right now?


Pretty hot, between 85 and 90 in most of the Northern Gulf.

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Quoting NOLABean:
What are GOM temps like right now?

hot hot hot!
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Quoting StormFreakyisher:
2. SHOWER ACTIVITY EXTENDING FROM THE EASTERN CARIBBEAN SEA ACROSS
HISPANIOLA TO THE TURKS AND CAICOS ISLANDS ARE ASSOCIATED WITH A
WESTWARD-MOVING TROPICAL WAVE. THERE ARE NO SIGNS OF ORGANIZATION
AND UPPER-LEVEL WINDS ARE CURRENTLY UNFAVORABLE FOR SIGNIFICANT
DEVELOPMENT. THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF
THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

I still don't understand why they say upper level winds are unfavorable for development when it is under 10knts of shear and moving into 5 knts.And it is moving into an area of decreasing shear from 5-10knts.And it will be moving into warmer waters from the Gulf stream in the Bahamas.This should be a code orange.




i cant help but to understand that it looks real impressive
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Take a look at the NHC page. They upgraded 90L to code red.
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I guess this is appropriate song for 90L.
Link
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Looking at the GFS it could be a close call whether the system impacts Florida than I originally thought. The GFS depicts a deep layered ridge south of the base on the deep layered longwave trough. The shortwave will have a ridge behind it. So steering gets a little complex.
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What are GOM temps like right now?
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Quoting jasoniscoolman10:


wow look at this map i see big time t.storm here..what is going on here.....,
Just a flare up of convection with minimal 850 MB vorticity, just something to watch, probably won't become anything except for a South Florida rain maker.
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looks like they gave it a 50%+ now
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i am still very intrested in the tropical wave north of hispaniola looks good and getting a circular look to it and headed for south florida
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Wow...

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2. SHOWER ACTIVITY EXTENDING FROM THE EASTERN CARIBBEAN SEA ACROSS
HISPANIOLA TO THE TURKS AND CAICOS ISLANDS ARE ASSOCIATED WITH A
WESTWARD-MOVING TROPICAL WAVE. THERE ARE NO SIGNS OF ORGANIZATION
AND UPPER-LEVEL WINDS ARE CURRENTLY UNFAVORABLE FOR SIGNIFICANT
DEVELOPMENT. THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF
THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

I still don't understand why they say upper level winds are unfavorable for development when it is under 10knts of shear and moving into 5 knts.And it is moving into an area of decreasing shear from 5-10knts.And it will be moving into warmer waters from the Gulf stream in the Bahamas.This should be a code orange.




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I just completed a 2hr Tropical Update...WOW! Here it is if anyone would like to view!
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting Drakoen:
The models appear to have a good handling on where this system will go in 5 days or so. After that is the problem.


This far out... I'm surprised that 90% agree on 90L being at a minimum close to the Northern Leeward Islands.
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Quoting jasoniscoolman10:


wow look at this map i see big time t.storm here..what is going on here.....,


A tropical wave is producing convection N of the Greater Antilles. Conditions are not conductive for development but some energy from the wave may arrive in the Gulf late this week into next week, where it could encounter a more supportive environment.
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Quoting JRRP:
Link
GFDL
WOW, looks like GFDL is now forecasting Hurricane inensity.
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Quoting Patrap:

Pat - it's firing up quite a bit this afternoon....
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TD2 is making a little comeback.
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TD2's convection has now gotten narrowed as it is being blown from the COC. Small patch still on the west side, but the majority of it is in danger of seperating completely.
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Quoting TreasureCoastFl:


With the tropics heating up I say 3906.. lol
funny about alcohol level, does the loser have to buy a round? ;)


LOL that's funny!
On serious note so I don't get blocked for playing... models show this in GOM at all?
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Quoting canesrule1:


Looks like they had to use quite a bit of Red Crayon to fill in 90L lol.
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"Right now due to the distance of 90L I can't give you an accurate path of where 90L will make landfall but i can say everyone on the eastern seaboard please monitor this system carefully, mostly the people in Florida because of model support", I can just imagine our local news saying that at the 5 O'clock news, lol.
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If I were in the islands and PR I'd be watching this one closely.
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Quoting JRRP:



HWRF likes to exagerate storm intensity in the moderate to long range with storms that are on the verge of developing.
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Quoting canesrule1:


lol!!!
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Quoting szqrn1:
Here is a poll.... how many blog reply posts will there be before Dr. Masters post another new blog... hmmm 3406 ! Na ,, kidding I dont want to calculate the votes. (Its like in the ER when we take bets on how high someone's alchohol level will come back!)... yes we do that!


With the tropics heating up I say 3906.. lol
funny about alcohol level, does the loser have to buy a round? ;)
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698. JRRP
Link
GFDL
Member Since: August 16, 2007 Posts: 0 Comments: 5474
The models appear to have a good handling on where this system will go in 5 days or so. After that is the problem.
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All this talk of heading up the East Coast,I think I might give a few more days before I run for cover here new england.
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I say 4674
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Red it is:

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The hurricane models are really responding to this system.
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Quoting PimpCane:


Actually, I don't think you can even say for sure that we'll have a substantial tropical cyclone in three days. We could, but I don't see it being a slam-dunk either. Just because it's in better surroundings than TD2 doesn't mean it has a free pass to rapid development. Be alert to the possibility, sure, but there's a lot of people out here making foolhardy predictions about island and even U.S. landfalls when the bloody thing's around the Cape Verde islands and not even a depression yet.



I agree with you but,

In looking at the models, would you agree that all of them show a substantial cyclone heading west in the C-Atlantic in 3 days?

I was merely saying that is the only thing the models are consistent on right now thus the only thing you can give a semi-accurate forecast on.
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Here is a poll.... how many blog reply posts will there be before Dr. Masters post another new blog... hmmm 3406 ! Na ,, kidding I dont want to calculate the votes. (Its like in the ER when we take bets on how high someone's alchohol level will come back!)... yes we do that!
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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.