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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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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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..
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hebert Boxes will also get ya pretty drunk...as i have sailed through both several times...and each time was pretty drunk...
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The " Herbert Box" now the fun will begin!!
Member Since: August 19, 2007 Posts: 0 Comments: 1601
Looks like S-FLA is in for a soaker on Saturday.

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Quoting Patrap:



"You Betcha"




LOL! Made my day.
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Quoting Chicklit:

It's "Hebert" and doesn't really exist.
There is no box that storms jump out of.
But there is a Santa Claus.


LMAO
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Quoting TampaSpin:
TD2 is entering into slightly warmer waters with a little less Dry and dusty air. The only thing it is keeping it from developing now is the shear from the east.


I think it is interesting that TD2 has moved somewhat north of due west. I wonder if this is what the HWRF was foreseeing. And if it is, that may be why it was showing TD2 becoming a hurricane.

the best part of that scenerio = "Fish"


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Quoting canesrule1:
All models take 90L through the Herbert box, which means, SFLA is in danger.

No it does not. The Herbert boxes are for Major hurricanes only and we can't tell the intensity now.
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Quoting canesrule1:
All models take 90L through the Herbert box, which means, SFLA is in danger.

It's "Hebert" and doesn't really exist.
There is no box that storms jump out of.
But there is a Santa Claus.
Member Since: July 11, 2006 Posts: 14 Comments: 11423
What is the "Herbert Box"?

Thanks.
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Quoting Drakoen:
Miami is not the only place that exists in South Florida



Ooooooh..JFV might have a Coronary if he see's dat un...
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Good God, Pat!!!!!!!!! That's scarier than any hurricane!!!!!!!!!!!
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Quoting canesrule1:
All models take 90L through the Herbert box, which means, SFLA is in danger.


Oh no, he brought up "The Box"
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ummm...well, maybe "Ain't no Stoppin' Us Now" would be a better song selection.
Loop
Member Since: July 11, 2006 Posts: 14 Comments: 11423
All models take 90L through the Herbert box, which means, SFLA is in danger.
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tampa does tat take 90l into the north and south carolina area?
Member Since: August 19, 2007 Posts: 0 Comments: 1601
Quoting Patrap:



"You Betcha"




LOL!!!
Member Since: October 28, 2006 Posts: 57 Comments: 30823
Quoting IKE:


Looks like dry-air on the NE side. Notice how that section is void of much convection.


That would make for somme intersting FEMA paperwork.

"Our community was impacted by Hurricane Bill on Aug 20. Four days later we were impacted by Hurricane Ana." LOL!!!
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There is very little at the lower levels in association with the convection north of Hispaniola that is interacting with an upper air low. Surface pressures are not falling.
Member Since: October 28, 2006 Posts: 57 Comments: 30823
865. IKE
Quoting WetBankGuy:
What does this mean for those of us living on the coast around, oh, 90W if something slips into the Gulf next week?

ALL MODELS AND ESP MEANS OF GFS/ECMWF INDICATE A ROCKIES RIDGE AND DOWNSTREAM TROF ALONG 90W 85W LATE PERIOD INTO LATE NEXT WEEK AND WEEKEND.


Should get turned NE. Could be a sign of an early fall...cooler temps...dryer air. GFS is depicting a deep trough.
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Quoting CaneWarning:


It looks like DR takes the brunt of the system.


Probably Pureto Rico first then DR
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting IKE:


It could. Just noticing the SAL....


I see it to Sir Ikester.... LOL, but IMHO, TD2 has cleared the path
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Miami is not the only place that exists in South Florida
Member Since: October 28, 2006 Posts: 57 Comments: 30823
861. IKE
Quoting Patrap:


I'm watching that area....headed right for south Florida, then the soup-bath GOM.
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Quoting Patrap:


hmmm, that wave there definitely seems to be doing something....
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I hear Dark Vader/Wagner music playing in 90L's background.
So far, this one is just 'Singin' in the Rain':
Member Since: July 11, 2006 Posts: 14 Comments: 11423
Quoting jeffs713:

One isolated thunderstorm = impressive now? If that is impressive, what would an actual hurricane be? "OMG-THIS-IS-INCREDIBLE"?

I think TD2 is more along the lines of "pathetic", "sad", "looking pretty bad", and "running out of time to turn things around".
LMAO, agreed!
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What does this mean for those of us living on the coast around, oh, 90W if something slips into the Gulf next week?

ALL MODELS AND ESP MEANS OF GFS/ECMWF INDICATE A ROCKIES RIDGE AND DOWNSTREAM TROF ALONG 90W 85W LATE PERIOD INTO LATE NEXT WEEK AND WEEKEND.
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Some of the models bring it through the Herbert Box....
Not good for Miami
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TD2 is entering into slightly warmer waters with a little less Dry and dusty air. The only thing it is keeping it from developing now is the shear from the east.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
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853. IKE
Quoting PanhandleChuck:


It's just getting started Ike, that thing could very well be one to remember.


It could. Just noticing the SAL....
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TAFB just came out with TD2's satellite estimate. Came out with T1.0/25kts and said "Could have gone with TWTC (too weak to classify)"
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Quoting Drakoen:
90L looks like West Pac invests lol

Definitely. They tend to start out as sprawling masses of clouds.
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90L needs deeper convection and more organization of its convective bands. Right now it's a broad circulation.
Member Since: October 28, 2006 Posts: 57 Comments: 30823
Hey Lefty!! I was thinking about you the other day. Hope that you and your family is doing okay. Good to hear from you.
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847. IKE
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TD-2 and Portion of 90L Viz Loop,FLASH
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Quoting IKE:


Surprised it's not higher....
me too, i would think 2.0
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90L looks like West Pac invests lol
Member Since: October 28, 2006 Posts: 57 Comments: 30823
Quoting weatherfan92:


I agree, quite an impressive turnaround.

One isolated thunderstorm = impressive now? If that is impressive, what would an actual hurricane be? "OMG-THIS-IS-INCREDIBLE"?

I think TD2 is more along the lines of "pathetic", "sad", "looking pretty bad", and "running out of time to turn things around".
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Quoting PanhandleChuck:


Now that's impressive
I wouldn't call it impressive, but i do have to say it does look like a weak TS.
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Quoting IKE:


Looks like dry-air on the NE side. Notice how that section is void of much convection.


It's just getting started Ike, that thing could very well be one to remember.
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Ike thanks for posting the vort map...

Looks like it went from no vort to actually having a little tendency
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Could be wrong but I'm thinking something could become of that area near the Bahamas.
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Quoting TampaSpin:
Not pretty picture.....lets hope this changes.



It looks like DR takes the brunt of the system.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
837. IKE
Quoting extreme236:


Um no?

13/1745 UTC 10.9N 23.4W T1.0/1.0 90L -- Atlantic


Surprised it's not higher....
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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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