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 Patrap:



Never say NO so far out,..nature has a way of making one er,blush real bad like.

Nothing is a Given with 90L.
Continue to Follow the NHC for the words on Track when and IF it forms


Yeah, the GOM is one of the main three possible tracks.
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As of right now, doesn't look to be much of recurving....

Link
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Quoting Drakoen:


He asked that based on the current models. With such a trough in place at this time I don't see anything going into the GOM. The HWRF, GFDL, CMC, GFS are tracking this thing towards the northern islands or even north of there. A series of successive shortwaves should erode at the ridge causing a system that forms in the tropical atlantic to move in a WNW fashion.


I don't think any models show this going into the GOM right now. This thing may be for the fishes, but it could be a very close call.
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Quoting cg2916:

What's the formula for translating non-surface winds into surface winds?


Varies on the height, from 80-95%. I looked at the actual model output at 126 hours, which on the FSU site shows surface winds of 107 kt.

http://moe.met.fsu.edu/tcgengifs/hwrf/2009081312-invest90l/slp21.png
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we now have a red circle around our 90L...
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August 23rd huh? I am getting butterflies in my tummy all over again.
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Quoting Patrap:



Never say NO so far out,..nature has a way of making one er,blush real bad like.

Nothing is a Given with 90L.
Continue to Follow the NHC for the words on Track when and IF it forms


He asked that based on the current models. With such a trough in place at this time I don't see anything going into the GOM. The HWRF, GFDL, CMC, GFS are tracking this thing towards the northern islands or even north of there. A series of successive shortwaves should erode at the ridge causing a system that forms in the tropical atlantic to move in a WNW fashion.
Member Since: October 28, 2006 Posts: 57 Comments: 30494
well TD2 convection is starting to go around the center if it get enough convection it will get stronger maybe 35mph TD at 5pm or 11pm and 90L looks good prob TD3 at 5pm or 11pm
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Quoting nrtiwlnvragn:


That image is 900 mb winds, the coresponding surface winds would be 106 kt.

considering the min SLP is 932 mb, 900 mb isn't so far from the surface (even at RMW). Standard reduction from 900 mb to the surface may not quite apply.
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Quoting nrtiwlnvragn:


That image is 900 mb winds, the coresponding surface winds would be 106 kt.

What's the formula for translating non-surface winds into surface winds?
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Quoting canesrule1:
the only way would be if it passed through Florida and into the gulf, but unfortunately some long range models are forecasting that.

Sux we gota act like the Gulf's barrier island to weakens storms before they hit the Gulf because we have to take all the damage but then again were used to it and don't want another storm hitting NOLA.
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Quoting Drakoen:


No.



Never say NO so far out,..nature has a way of making one er,blush real bad like.

Nothing is a Given with 90L.
Continue to Follow the NHC for the words on Track when and IF it forms
Member Since: July 3, 2005 Posts: 424 Comments: 128347
atmo, my mon...Is the carib AOI represented by the northern Bahama possibility? Or is that sumpin' else?
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Quoting jasoniscoolman10:
ok...


Looks like 02 may be around for a while.
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Quoting Drakoen:
CMC long range from 00z


Whats that in the GOM?
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Quoting TerraNova:
Wow...



That image is 900 mb winds, the coresponding surface winds would be 106 kt.
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Quoting WxLogic:


Don't forget about the poor if you win...


I never win anything but, surely won't forget where I come from if I do.
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769. slavp
Quoting CaneWarning:


Ew.
Agree, Plus that low in the northern gulf
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Quoting louisianaboy444:
Could 90L enter the Gulf based on what the models are saying?


No.
Member Since: October 28, 2006 Posts: 57 Comments: 30494
Quoting louisianaboy444:
Could 90L enter the Gulf based on what the models are saying?
the only way would be if it passed through Florida and into the gulf, but unfortunately some long range models are forecasting that.
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Quoting Drakoen:
CMC long range from 00z


Ew.
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The NHC has a history of upgrading a system to TD status on the same day as the put the red circle around it, they did it to every single storm in the EPAC.
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Quoting cchsweatherman:


How eerily reminiscent.



Historical Climatology at work,nothing eerie there.

As Gustav last year Had NOLA evacuating on the 29 August,a significant anniversary,but still Historical Climatology
Member Since: July 3, 2005 Posts: 424 Comments: 128347
The statistical genesis crew isn't impressed with the Caribbean AOI:


The parameter holding that back is the lack of convergence (none or very minimal):

From: http://www.ssd.noaa.gov/PS/TROP/TCFP/atlantic.html

Also evident in the CPC plots:

From: http://www.cpc.ncep.noaa.gov/products/hurricane/

All of the above posted in my blog.
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Current NAO Forecast


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Could 90L enter the Gulf based on what the models are saying?
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CMC long range from 00z
Member Since: October 28, 2006 Posts: 57 Comments: 30494
Quoting TheCaneWhisperer:


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}


Don't forget about the poor if you win...
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GOM 60 Hour Surface Current Forecast,Loop current
Member Since: July 3, 2005 Posts: 424 Comments: 128347
Quoting TerraNova:


HWRF does that a lot with developing systems in this area; it did the same thing with Dean in 2007 (which did end up becoming a Cat 5 but much, much further west). It means little to nothing.


It put Felix as a Category 5 at Tampa Landfall.
Felix did end up being a Category 5, but not a Tampa Landfall. GFDL's also making 90L a Hurricane just not as strong.
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Quoting Drakoen:


August 23rd according to the GFS


How eerily reminiscent.
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Quoting Skyepony:
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..


Went swimming past weekend with my daughter and water temps off Jupiter are roasting. It felt like I was stepping into a warm bath, hardly relieving. Yellow circle covers their butts, still looking over my shoulder though.
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Quoting Seflhurricane:
hey drak according to the models when next week does it make its closest approach to south florida or florida


August 23rd according to the GFS
Member Since: October 28, 2006 Posts: 57 Comments: 30494
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.

Way, way, way too early to worry if a system (that has not even yet developed) will impact Fl or not. We're talking 10-12 days out. Heck, the NHC 5 day track forecast error on a mature storm is several hundred miles.
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Quoting TerraNova:
Wow...



Is that 142 knots? If so that would be 161 mph winds! Wow.
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Since 90L is now red, I give it a 30% chance of being a TD tonight, a 60% chance of it being a TD tommorow, and a 95% chance of it being a TD. Also, I give it a 70% chance of becoming a TS.
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747. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 5838
746. 7544
yellow got longer for our 65w wave thats looking better and better
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Quoting HurricaneKyle:


That's a 164 MPH Category 5 Hurricane.


HWRF does that a lot with developing systems in this area; it did the same thing with Dean in 2007 (which did end up becoming a Cat 5 but much, much further west). It means little to nothing.
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Quoting HurricaneKyle:
I guess this is appropriate song for 90L.
Link

That so reminds me of THIS THEME SONG for 90L!Scary!Link
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Quoting StSimonsIslandGAGuy:
Hmm maybe it will be drawn up to Georgia like Hurricane David was, Drakoen.


You had better hope not!
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We should see a TCFA soon with 90L. It would appear here.
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RED ALERT AND TD2 AND YELLOW
WE WILL SEE ALOT MOER OF THIS ON TWC NOW
Link
AND
Link
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Quoting NOLABean:
What are GOM temps like right now?




GOM 60 Hour SST Model,area specific
Member Since: July 3, 2005 Posts: 424 Comments: 128347
Quoting TerraNova:
Wow...



That's a 164 MPH Category 5 Hurricane.
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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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.