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 OSUWXGUY:
Drak-

I'm probably spending too much time analyzing a models output...

As you discussed, there is a weak initial trough, followed by a stronger second trough over the Eastern US as 90L is forecast to approach.

By looking at the Northern Pacific section of the GFS, it appears the source region for the jet streak that digs the second, stronger trough is in the Central Pacific. Obviously still a long way aways, but we'll probably have to watch this in coming runs.

Link



Yes we will have to watch it
Member Since: October 28, 2006 Posts: 57 Comments: 30494
B... Im in FL I can still vote... I vote for B
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12Z HWRF running... wanting to make 90L a TD in 12HR or so and a TS in 24HR to 36HR from the looks of it.
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Quoting bcn:


"a"

This year first named storm will start between Azores & Canarian Islans


Anything to support that? Model support? AOI?
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Who thinks 90L might do a Hanna 08' type of turm when it nears Florida.
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Drak-

I'm probably spending too much time analyzing a models output...

As you discussed, there is a weak initial trough, followed by a stronger second trough over the Eastern US as 90L is forecast to approach.

By looking at the Northern Pacific section of the GFS, it appears the source region for the jet streak that digs the second, stronger trough is in the Central Pacific. Obviously still a long way aways, but we'll probably have to watch this in coming runs.

GFS North Pacific Sector
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630. bcn
Quoting btwntx08:
poll time what is the 2pm TWO gonna say 90L:

A.same orange
B.red
c.td
vote now poll closes in 20 minutes


"a"

This year first named storm will start between Azores & Canarian Islans
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Quoting 954FtLCane:
although obviously still way too early I remember Andrew almost dissapearing before it made the turn and became a monster.. hmm 11 days from now would be the 17th anniversary

pearing before
yup i remember
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Quoting leftovers:
good i can tell them about my broken computer while browsing here


Same. Even though I removed the virus. I still get the blue screen sometimes. Computer has physical memory issues now. Thanks Wunderground!!!
Member Since: October 28, 2006 Posts: 57 Comments: 30494
Quoting CaneWarning:


Are you sure you are the baby daddy?
lol storms bring out the worst in people
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http://www.ssd.noaa.gov/goes/east/carb/avn-l.jpg
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Quoting OSUWXGUY:


I think that maybe the proximity to land you mention is similar to the entraining dry air choice? Or maybe I'm misunderstanding your point?

Any frictional effects from land on convergence in the northeast would enhance convection - although given the distance these would be small.

Streamlines indicate the source for this air is the Sahel/Saharan region which would have lower RH.


You got it... and I'm with you.
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although obviously still way too early I remember Andrew almost dissapearing before it made the turn and became a monster.. hmm 11 days from now would be the 17th anniversary

pearing before
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Quoting WeatherStudent:



grow up, drak.
no actually a miami hit seems very reasonable, lol, just kidding with u.
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Quoting WxLogic:


Wouldn't be to to the proximity to land still? I would assume the bands on the southern quadrant could start building up towards the east later today and closing it it up some.


I think that maybe the proximity to land you mention is similar to the entraining dry air choice? Or maybe I'm misunderstanding your point?

Any frictional effects from land on convergence in the northeast would enhance convection - although given the distance these would be small.

Streamlines indicate the source for this air is the Sahel/Saharan region which would have lower RH.
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Quoting WeatherStudent:
yup, it'll be us hitetr alright, with taht ridge in place, you knwo it. if itw ere setember or october clearly a fish, but in aug, olvidalo.


Really?
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Well, I'm out,
Good night one and all, Will try to catch the Barometer Bob show in the morning.
Stay safe, Play safe, Blog safe.
Cheers AussieStorm.
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613. 7544
going with orange for 90l

but the 65 west wave is getting bigger hmmm might be something also to watch closer to home
Member Since: May 6, 2007 Posts: 0 Comments: 6812
Quoting WeatherStudent:
sf get ready


Why does San Fran need to get ready? LOL
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I say orange, but red tomorrow.
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Anyone got a QS on TD2? COC looks a bit elongated on RGB.
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Quoting presslord:



...well...as I live in South Carolina...I won't be saying much on this subject....

Easy! :)
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Quoting Drakoen:


Maury said I was


HA!

90L is one to watch...
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Looks like a TD trying to form above Dominican Republic Big flare up in the last several hours, I think two o clock update will show concern for this area
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Quoting Drakoen:
Convection associated with 90L remains poorly organized. Convective bands are evident.
maybe, i still think red at the TWO, it should be out within 15 minutes.
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What scares me about the NOGAPS is that it keeps TD2 well and alive, and 90L hitting the Antilles.
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Quoting TheCaneWhisperer:
Run to Run track consistency with ANY model right now is NIL. These models don't have a clue beyond 3 days with 90L. The only thing consistent that you can forecast with a shred of credibility is that there will be a substantial tropical system in the Central Atlantic in 3 days moving west.


Amen.
Absolutely
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Quoting Drakoen:
ZOMG MIAMI HIT !?!?!?! I am putting up shutters as we speak!!!


LOL
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Quoting CaneWarning:


Are you sure you are the baby daddy?


Maury said I was
Member Since: October 28, 2006 Posts: 57 Comments: 30494
Run to Run track consistency with ANY model right now is NIL. These models don't have a clue beyond 3 days with 90L. The only thing consistent that you can forecast with a shred of credibility is that there will be a substantial tropical system in the Central Atlantic in 3 days moving west.
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the admins will be here shortly, keep on topic.

bbl
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Convection associated with 90L remains poorly organized. Convective bands are evident.
Member Since: October 28, 2006 Posts: 57 Comments: 30494
Quoting Drakoen:
NOT taking any chances guys and i've left my baby in my baby mama's care


LOL @ "baby mama".. you guys are funny.
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Quoting Drakoen:
NOT taking any chances guys and i've left my baby in my baby mama's care
me neither, lol
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Quoting btwntx08:
poll time what is the 2pm TWO gonna say 90L:

A.same orange
B.red
c.td
vote now poll closes in 20 minutes


I go with B... should be a TD by tomorrow. As long as it doesn't explode later today.
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Quoting Drakoen:
NOT taking any chances guys and i've left my baby in my baby mama's care


Are you sure you are the baby daddy?
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Quoting canesrule1:
U live in SFLA with me and Duffy, lol, what do u think of the CMC?


As a person who lives in West Palm Beach, i'm watchin' out.
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Exactly who gets to decide storm names? Next year, I'd like to see TS Batman. That would be far more entertaining that "Bill", IMO...
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Red probably 2am or 8am Friday, at the current rate of organization.
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NOT taking any chances guys and i've left my baby in my baby mama's care
Member Since: October 28, 2006 Posts: 57 Comments: 30494

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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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