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 CaneWarning:


Could be. Let's hope.
I'm getting confused now....Which one 90L or TD2?
Member Since: Posts: Comments:
fish to who? the US?
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Any body want to talk about the GFS showing Development in the GOM. I know the pressure drop is minimal but the precip increase might be just what East Texas is looking for.
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Quoting Vortex95:


TD2 will be entering an area of lower shear by tommorow.


It's in relatively weak shear now anyway.

15 kts or so. Maybe 10 tomorrow, but neither are oppressive.
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Broad system:
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Quoting Patrap:



"You Betcha"





And she can see 90L from her house........Sorry
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Quoting BiloxiGirl:
What are the chances we could have a GOM Coast event at any point next week? There is so much to watch I can't keep up with it just checking in here and there.


Either 100% or 0%. We just don't know which one yet.
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Quoting LPStormspotter:


so we looking at fish storm?


possibly.

Member Since: March 19, 2009 Posts: 0 Comments: 1421
I am starting to think that 90L may be a threat for the fish, but then again, models do change.
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Quoting LPStormspotter:


so we looking at fish storm?


Could be. Let's hope.
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90L resembles pre typhoons in the Western Pacific
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Quoting Weather456:
Code: Red
Location: 116N-225W
Winds: 30 mph
Pressure: 1009 mb

I expect TD 3 sometime between Friday and Sunday.


That looks pretty impressive. And HUGE.
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Quoting wunderkidcayman:
hey guy the convection from 90L rainbands are going into TD2 so TD2 is feeding off of the bands of 90L



loop
Link


You got it backwards, 90L is feeding into TD2.
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Quoting Drakoen:
Euro 12z puts it no where near the east coast


so we looking at fish storm?
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Quoting seminolesfan:
Just deal. Life is too short. Hit refresh again and go on living...


Wow.. wake up on the wrong side of your face. Geese
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Code: Red
Location: 116N-225W
Winds: 30 mph
Pressure: 1009 mb

I expect TD 3 sometime between Friday and Sunday.

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Praia, Cape Verde (Airport)
Updated: 1 hr 1 min 47 sec ago
Mostly Cloudy
82 °F
Mostly Cloudy
Humidity: 64%
Dew Point: 72 °F
Wind: 12 mph from the NNE
Wind Gust: -
Pressure: 29.87 in
Visibility: 11.0 miles
Clouds:
Scattered Clouds 1575 ft
Mostly Cloudy 2362 ft
(Above Ground Level)
Elevation: 89 ft
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Quoting Patrap:

Well, it's huge, new, and being sucked up by TD 2
ope,


..im not going to say nuthing,..Im suppressing my Evil Side..

I could've stated that better. It is huge, only been out for a few days, and TD 2 is feeding off of part of it.
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965. slavp
Quoting Patrap:

Well, it's huge, new, and being sucked up by TD 2
ope,


..im not going to say nuthing,..Im suppressing my Evil Side..
LMAO
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Wind shear over 90L

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Well, it's huge, new, and being sucked up by TD 2
ope,


..im not going to say nuthing,..Im suppressing my Evil Side..
Member Since: July 3, 2005 Posts: 428 Comments: 129838
Wow. Thanks for all of the good GOM temp info, guys :)
Is that on par for this time of year?
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Euro 12z puts it no where near the east coast
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Member Since: July 3, 2005 Posts: 428 Comments: 129838
Quoting CaneWarning:


Well that's not so bad.
I think the curve is to far out, i'm anticipating the curve (if it does curve) to be very close to Florida.
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Quoting wunderkidcayman:
hey guy the convection from 90L rainbands are going into TD2 so TD2 is feeding into the bands of 90L



loop
Link

Yeah, TD 2 is maintaining its convection, too.
Quoting Drakoen:
90L's convection is very unimpressive

Well, it's huge, new, and being sucked up by TD 2.
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TD2 looks better (like that was difficult), but that may only be for the moment. Anytime it tries to get convection over its COC (like now), it gets blown off it again.

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Quoting futuremet:
12Z ECMWF


Well that's not so bad.
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High my name is weatherstdent nd teh tyme iz 2:55 PM.
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Quoting canesrule1:
All models take 90L through the Herbert box, which means, SFLA is in danger.


XD
Member Since: May 17, 2009 Posts: 0 Comments: 559
Quoting FSUCOOPman:


4.765% chance.

No more. No less.

/sarcasm


I prefer you take that out at least 10 decimal places...
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12Z ECMWF
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Quoting fire635:
"JeffMasters does not have any blog entries."

This is getting annoying.


Maybe they are trying to give you a hint??
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90L's convection is very unimpressive
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Quoting TampaMishy:
I never see wind here..I'm further in I suppose then yourself?


I always have a breeze at my house. It's windy now but there are storms all around us.
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hey guy the convection from 90L rainbands are going into TD2 so TD2 is feeding off of the bands of 90L



loop
Link
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Quoting BiloxiGirl:
What are the chances we could have a GOM Coast event at any point next week? There is so much to watch I can't keep up with it just checking in here and there.


4.765% chance.

No more. No less.

/sarcasm
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Quoting CaneWarning:


Not really!
I never see wind here..I'm further in I suppose then yourself?
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Quoting TampaMishy:
It's getting windy here in Tampa which is very unusual.


Its not that uncommon when storms are heading your way.
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90L is under a low amount of shear right now!

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Quoting fire635:
"JeffMasters does not have any blog entries."

This is getting annoying.
Just deal. Life is too short. Hit refresh again and go on living...
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Quoting GoodOleBudSir:


That would be: "teh 'WS' typing course"


Yup! I forgot teh most important part.
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Quoting TampaMishy:
It's getting windy here in Tampa which is very unusual.


Not really!
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What are the chances we could have a GOM Coast event at any point next week? There is so much to watch I can't keep up with it just checking in here and there.
Member Since: August 15, 2006 Posts: 0 Comments: 56

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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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