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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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.
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Ok someone clue me in to whats blowing up around the bahamas?
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Quoting PennGator:

Td #2 might benefit from the trailing moisture following on the west side of 90l


er... do you mean the east?
Member Since: October 15, 2008 Posts: 11 Comments: 2312
"JeffMasters does not have any blog entries."

This is getting annoying.
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Quoting Drakoen:
The Euro isn't out yet

I have early access as it comes out. You'll see what I'm talking about.
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The 12z Euro looks like it takes an Irene 2005-like path...goes between Bermuda and the US as a near miss hurricane.
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Quoting fmbill:


Actually...it is starting to look like the circulation over Africa is starting to interfere with 90L.

It seems the waves are too close to each other this year.

Td #2 might benefit from the trailing moisture following on the west side of 90l
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Quoting SQUAWK:


I see you have taken the "WS" typing course.


That would be: "teh 'WS' typing course"
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It's getting windy here in Tampa which is very unusual.
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Quoting cg2916:

Don't forget TD 3 by today.
Also, varying forms of 'you type like WS'.
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The Euro isn't out yet
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Quoting cg2916:

Don't forget TD 3 by today.


Wow, TD 2 looks impressive. We may have to worry about Hebert Boxes, initiating a code red. And we might have TD 3 by the end of the day!
Member Since: October 15, 2008 Posts: 11 Comments: 2312
Quoting rareaire:


OBAMA? LOL just kidding ya.


No your not........LOL
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting Patrap:
how do i get that link
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Quoting canesrule1:
The Things most said today are:

1. Impressive
2. Hebert Box
3. IT'S CODE RED!!!!
and #4. TD#2 looks impressive!

Don't forget TD 3 by today.
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Some would Argue that Darth Vader was simply stompping out rebellion.
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Quoting SQUAWK:


I see you have taken the "WS" typing course.


if ya can't beat 'em, join 'em...
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The Things most said today are:

1. Impressive
2. Hebert Box
3. IT'S CODE RED!!!! 4. TD#2 looks impressive!
5. TD 3 by today.
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Quoting presslord:



This is very importasnt science we're talkin' about here...please don't msake light of it...


I see you have taken the "WS" typing course.
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12z Euro through 204 looks like a recurve.
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.
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916. slavp
Quoting Patrap:


Ooooohhhhhhhhhhhh, I like dat one Chicklit..shes got the er,,room fer that.
As long as she don't inhale
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Quoting Drakoen:
The models don't agree on the strength of the long wave trough. The CMC is keeping it somewhat week. The ECMWF is the strong and has lower to mid level amplification at the base of the trough. The GFS is in between.


You would think that since the trough is actually coming from Canada that you would lean more towards the CMC model as it is meant more for them than for us.
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Stupid Question Time:

Folks are talking about how large 90L is...
Looks like a huge area of clouds south of Cape Verde Islands to me, however, how much actually belongs to 90L? All of it?

6N-16N long?
16W-34W wide?

TIA
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Quoting MrNatural:
There appears to be some interaction between TD2 and invest 90. Looks like invest 90 will win out.


Actually...it is starting to look like the circulation over Africa is starting to interfere with 90L.

It seems the waves are too close to each other this year.
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Quoting Drakoen:
Miami is not the only place that exists in South Florida


Ya why is it every time somebody says South Florida they think only Miami is in South Florida.
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Quoting Chicklit:

Maybe Sarah Palin can suck it up with that big mouth of hers and spit it out in Lake Okeechobee.


Thanks a lot for loading me up with THAT visual...
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Quoting TexasHurricane:


Yeah, this area may need to be watched closely after all....wasn't looking to impressive at first. Now though, hmmmmmm.
still not looking impressive, but it is growing convection wise.
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Quoting Drakoen:
Miami is not the only place that exists in South Florida


LOL!
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Quoting canesrule1:
Looks like S-FLA is in for a soaker on Saturday.



Yeah, this area may need to be watched closely after all....wasn't looking to impressive at first. Now though, hmmmmmm.
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Quoting hahaguy:


Are you sure you weren't drunk before lol.



This is very importasnt science we're talkin' about here...please don't make light of it...
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Quoting spathy:
Pat and Ike.
Could that ull w of Fl pick up some energy from the blob above PR?
And do something with it.



Ooohhh,,thats way out my League spathy,..Im more a Observer,..than anything Like a Met. Maybe someone else can field dat one
Member Since: July 3, 2005 Posts: 428 Comments: 129904
Quoting Patrap:
Press..I had a Nightmare where Sarah Palin was Head of FEMA and JFV was Dep Director and a Cat- 5 Struck the South Carolina ,North Carolina Border,..and well..they sent all the Aid to Middle Carolina..


lmao!!!
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Hebert In a Box

Member Since: July 3, 2005 Posts: 428 Comments: 129904
Quoting SQUAWK:


What is "Dark Vader?"

oops Darth? The guy with all the evil in the world locked up inside his tiny brain?
Member Since: July 11, 2006 Posts: 14 Comments: 11424
Quoting NOLaHSE:
What is the "Herbert Box"?

Thanks.
I gotta fiver on the explanation going backwards from how Hebert worded it!
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Hey guys, what are the models forecasting Intensity wise for 90l at peak strength? Thanks in advance
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Quoting presslord:
hebert Boxes will also get ya pretty drunk...as i have sailed through both several times...and each time was pretty drunk...


Are you sure you weren't drunk before lol.
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pat...that sounds just about right...
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The models don't agree on the strength of the long wave trough. The CMC is keeping it somewhat week. The ECMWF is the strong and has lower to mid level amplification at the base of the trough. The GFS is in between.
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There appears to be some interaction between TD2 and invest 90. Looks like invest 90 will win out.
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Quoting Chicklit:
I hear Dark Vader/Wagner music playing in 90L's background.
So far, this one is just 'Singin' in the Rain':


What is "Dark Vader?"
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Quoting weatherwatcher12:

No it does not. The Herbert boxes are for Major hurricanes only and we can't tell the intensity now.
Yes i know.
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I have a question:

90L is a large, large wave. What is going to happen when the eastern fringes of 90L starts coming into range of TD 2's circulation. Would it give TD some moisture and allow it to wrap around it's own circulation, or, am i thinking way off course? What is clear is that TD 2 needs moisture in order to close off that impressive circulation... therefore could one think along the lines I am thinking with respect to a possible turnaround in circumstances for the storm?
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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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