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 Gustavike:
The GFS showed a smooth bullfight 06 today z but to 12 z reaffirms that a great hurricane could affect to the Antilles Majors within 180 hours. Meanwhile the TD2 does not occur by won and develops convection again. I believe that the future of this system is still uncertain Dr Jeff.


It looks like it would eat the islands, then PR, then Haiti.
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Quoting Weather456:
But can we be so unlucky to get the remnant of TD 2 and still 90L?

Bonnie and Charley?

Good Example
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About 1-2 days ago I might have been worried that 90L would swallow up TD2 and strengthen, but now, looking at size comparison, on the very off-chance that that would happen, it would be like adding a few drops to an almost full gas tank. 90L is HUGE.
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Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting WeatherStudent:
DRAK, TEH THROUGH WILL NOT BE TEH POTENT, GEEZE YOUR MAING IT SOUND AS if it's gonna be an early november through.


T... H.... E..... Type it slowly. THE is spelled THE. Im sorry. I have watched you spell the TEH for many many days now. I just couldnt help myself.
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The GFS showed a smooth bullfight 06 today z but to 12 z reaffirms that a great hurricane could affect to the Antilles Majors within 180 hours. Meanwhile the TD2 does not occur by won and develops convection again. I believe that the future of this system is still uncertain Dr Jeff.
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You are more than welcome!! Praying everything stays out of the Gulf! Do not want to do anything like IKE again. Have a nice day!
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Quoting WeatherStudent:


It's naotiously known for that, drak.


Say what????
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Quoting Acemmett90:

facts pressures droping like a rock and its getting better organised and almost all of the modle are projecting a florida hit


what link shows pressure "dropping like a rock"?...and organization still has a ways to go...and models to florida are long range 12 days+ which should not be taken for pure fact (its gonna happen)...
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90L looking better and better each frame, convection going into the center.
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Quoting Drakoen:
OBX then New England hit lol


If that did happen, Joe Bastardi would have a field day gloating about his forecasts.
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475. slavp
Quoting presslord:



ya might wanna check your keyboard....I think someone may have rearranged the keys...
LMAO!!!!
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Quoting P451:


I think once the convection tightens in closer to the center they might classify it.

I think it's a no-brainer that this will be a TD and then a TS.

Can't see this one fading. In fact for such a large system it sure seems to have gotten it's act together rather quickly.

That's a 20 hour loop.
yup
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Hi guys - first post of the year since I'm a reader more than a poster. Thanks to my location am much more interested in the Atlantic season ramp-up than other areas.

Have been seeing a few allusions around here by local mets that they are starting to watch the GOM a little. I'm thinking nothing to worry about except maybe a potential heavy rain maker... any thoughts? I get that the lingering trof could pose some development, but is there really enough time for anything to happen out there outside of maybe a TD3 at best?
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Quoting presslord:



ya might wanna check your keyboard....I think someone may have rearranged the keys...


clever :)
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Quoting 900MB:


What day is this model indicating?


Around 279-300 hours.. not accurate, but this has been a possible trend. It will definitely impact the Lesser Antilles in some way, if it were to recurve it can't recurve until after it passes south of Bermuda. So ALL of the East Coast needs to closely monitor the progress of 90L. Would not surprise me to see a code red by 2 p.m. with how it's been organizing. Just needs deep convection which should happen tonight.
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Quoting IKE:


I know you know this....that is way too far in advance to rely on any of what it says.

GFS may be overdoing the trough(strong...down to the gulf-coast). It may be delayed by a few days or sped up by a few.

I can see with my eyes out to about a week and that's a stretch.


LOL... quite true IKE. To me is more like a training exercise to be able to get a general feel about the trends. :)
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Quoting reedzone:
This run is not looking good for Long Island, NY.. It catches the trough but high pressure looks to build in and keep it from moving east.

12Z GFS 276 .. A stronger storm then the 06Z run.
Must remember that the 12Z and 00Z runs are more accurate then the 06Z and 18Z runs.



Yea good thing thats a long way out - we don't need a hurricane
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Quoting presslord:



ya might wanna check your keyboard....I think someone may have rearranged the keys...


LMAO!!
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OBX then New England hit lol
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Quoting Txrainstorm:
Thanks to all of you bloggers that helped and donated to the communities around my home after Ike. Patrap,Jeff Masters,Presslord,stormjunkie! You are all lights at that dark port!! I made my donation! You might need them in the near future. Make your donation today @ portlight.org



Thank you for the Kind words and for your continued support.

Patrick
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Quoting Acemmett90:

the scary thing is i rarely get feelings like this i am just worried that this could kill alot of people and some people on this blog are not realizing this


Had to come out of lurking mode for this. People realize this, they're just not panicking. This isn't even a storm yet. Use common sense, analyze it, pay attention to it, but it's way too early to post nothing but doom and gloom because of a gut feeling.
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GFS 192 Hours 500mb
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Quoting jasoniscoolman10:
LMAO, 02L is soooooooo small compared to 90L, lol
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460. 900MB
Quoting KEEPEROFTHEGATE:
yes wu has enable a popup for links to show what it is and to warn you you are going to a site outside of wu ya got to read what it says if its not what your looking for don't click it if ya got good security software scan it before ya go to link to check

Thanks. I guess I'll just trust the storms, ikes, and draks.
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Quoting presslord:



ya might wanna check your keyboard....I think someone may have rearranged the keys...
ROFLMAO
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90L... you can see the size comapred to 02L on the far left of the image.
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But can we be so unlucky to get the remnant of TD 2 and still 90L?

Bonnie and Charley?

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Let's start counting! lol.

Surface
Condition Points
A circulation is evident using visible satellite, shortwave infrared, microwave imagery or QuikSCAT/Windsat ambiguities
3 points
A circulation has been evident for at least 24 hours
5 points
A westerly surface- or gradient-level wind of 5 kt that is within 200 nm (370 km, 230 mi) south of the centre of the disturbance
5 points
Any wind associated with the system is at least 20 kt
2 points
Any wind associated with the system is at least 25 kt
3 points
Any wind associated with the system is at least 30 kt
4 points
A weather station within 200 nm of the system has reported had a pressure drop of 2 mb over 24 hours
3 points
A weather station within 200 nm of the system has had a pressure drop of 3 mb over 24 hours
4 points
The estimated MSLP of the system is less than 1010 to 1009 mb
3 points
The estimated MSLP of the system is 1008 mb or less
4 points

[edit] 500 mb height
Condition Points
There is evidence of at least an inverted trough
2 points
There is evidence of a closed circulation in the system
4 points

[edit] 200 mb height
Condition Points
Westerly flow of at least 15 kt over the disturbance
-4 points
There is evidence of anticyclonic outflow over the centre of the disturbance
4 points
Easterly flow of at most 20 kt over the disturbance
3 points

[edit] Sea surface temperature
Condition Points
The sea surface temperature is 26 Celsius (78.8 Fahrenheit) or higher
3 points

[edit] Satellite data
Condition Points
The system has persisted for at least 24 hours
3 points
The system has persisted for at least 48 hours
4 points
The system has persisted for at least 72 hours
5 points
The system has a Dvorak classification of T1.0 to T1.5 from all three agencies (TAFB, SAB, AFWA)
3 points
The system has a Dvorak classification of T1.5 to T2.0 from all three agencies
5 points
The Dvorak final-T number has decreased by T0.5 to T1.0 from two or more agencies
-2 points

[edit] Miscellaneous
Condition Points
The cloud system is north (or south) of 5 degrees latitude
3 points
The tropical system is within 72 hours of reaching a Department of Defense resource
3 points
The cloud system center and the satellite centre fixes for the system are within 2 degrees of each other
2 points
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Quoting presslord:



ya might wanna check your keyboard....I think someone may have rearranged the keys...

LMAO.
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Quoting WeatherStudent:
exactly, wx, if itw ere early, mid, or even late september i would ahve had more faiath in taht trhough, but its august for the love of god, emaning that the ridge still rpevails throughout most of the basin, which will affect tc.


Why do you make some of your posts so hard to read?
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Quoting Drakoen:


I saw that. The track still looks to take it over some mountainous areas over Haiti. The GFS always likes to strengthen the Azores high as a trough approaches. That trough is very potent and the ECMWF depicts that.


True... with a more pronounce turn after 55W or so... will be interesting to see if the 12Z run of the ECMWF still agrees with the trough strength.
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451. 900MB
Quoting reedzone:
This run is not looking good for Long Island, NY.. It catches the trough but high pressure looks to build in and keep it from moving east.

12Z GFS 276 .. A stronger storm then the 06Z run.
Must remember that the 12Z and 00Z runs are more accurate then the 06Z and 18Z runs.



What day is this model indicating?
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Quoting P451:


Looks like the center is finally starting to close off with convection, Probably one burst of DMAX convection and a Tropical Depression is born tomorrow morning. It's organizing quite well today.
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Quoting WeatherStudent:
exactly, wx, if itw ere early, mid, or even late september i would ahve had more faiath in taht trhough, but its august for the love of god, emaning that the ridge still rpevails throughout most of the basin, which will affect tc.



ya might wanna check your keyboard....I think someone may have rearranged the keys...
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Quoting 900MB:
P.S.- Is it safe to click on links yet? Did they fix the virus problem? Thanks, 900MB
yes wu has enable a popup for links to show what it is and to warn you you are going to a site outside of wu ya got to read what it says if its not what your looking for don't click it if ya got good security software scan it before ya go to link to check
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Quoting P451:
Very impressive, i think it should be classified as a TD, it already has all the standards a TD needs.
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Quoting WeatherStudent:
DRAK, TEH THROUGH WILL NOT BE TEH POTENT, GEEZE YOUR MAING IT SOUND AS if it's gonna be an early november through.


I'll answer this Drak....Teh Through will be as potant as advetized.
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Quoting WxLogic:
12Z GFS Shifted back to the left as expected... is having a little hard time timing the trough that will pull it WNW to NW and the strength of the building High after the trough departure.


I saw that. The track still looks to take it over some mountainous areas over Haiti. The GFS always likes to strengthen the Azores high as a trough approaches. That trough is very potent and the ECMWF depicts that.
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Quoting canesrule1:
very exposed center with a little patch of convection, i think its over with 02L, just my personal opinion.


I wouldn't count it out yet, looks like its not being sheared as much as yesterday but it still has to deal with the SAL.
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441. IKE
Quoting WxLogic:
12Z GFS Shifted back to the left as expected... is having a little hard time timing the trough that will pull it WNW to NW and the strength of the building High after the trough departure.


I know you know this....that is way too far in advance to rely on any of what it says.

GFS may be overdoing the trough(strong...down to the gulf-coast). It may be delayed by a few days or sped up by a few.

I can see with my eyes out to about a week and that's a stretch.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Thanks to all of you bloggers that helped and donated to the communities around my home after Ike. Patrap,Jeff Masters,Presslord,stormjunkie! You are all lights at that dark port!! I made my donation! You might need them in the near future. Make your donation today @ portlight.org
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that's a big trough for August that the GFS has coming down.

it still shows it just offshore of SE FL and heading up to the Outer Banks.

forward speed and strength of the trough and Bermuda high are gonna determine where this ends up.
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Quoting Weather456:
Eevery met office in the Leewards are talking about 90L


Not surprising. They have very good reason to do so.
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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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