Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. 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 was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


Figure 1. The remnants of Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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Member Since: Posts: Comments:
Quoting StormW:
Good evening!

2 good preparedness brochures


UNLEASHING NATURE'S FURY


AGAINST THE WIND
evening storm looks like we may have 2 TDS within the hour god help us here in South Florida
Member Since: July 14, 2009 Posts: 0 Comments: 3022
I've yet to notice the NHC officially classify a system without renumbering it first, but I can't say it couldn't happen since I don't know.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Latest 00Z Dynamical Models


Notice the white line indicating the Official forecast. This will likely be the path the NHC uses when they start re-issuing advisories on Tropical Depression 2.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
02L moving SW?

RAMSDIS IR Satellite
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Quoting Weather456:



TD 2 was re-designated, 90L was never renumbered, not yet.
oops, my bad, i miss read it, i think im overdue on the Heineken, if u know what i mean, lol.
Tampa my prediction on td-2 looking better and better!!!!
Member Since: Posts: Comments:
2726. snotly
Quoting MississippiWx:
I'm sure most people on here could do a better job at presenting the weather than the people on TWC. All that TWC is in it for now is show-boating and trying to impress their audience.

Example: Storm Master G!! Seriously, WTF???

Whatever happened to just giving the weather and how it is and leaving it at that?

Nonetheless, I never listen to TWC when it comes to tropical weather. I get much better info on this blog and just doing research myself.


Agreed,way overdone WC!

Confucius says: Man who wants to know the weather should look out the window.
Member Since: Posts: Comments:
can someone help me figure out why the model run links that are posted dont work for me?
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LOL storm master G

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Quoting SavannahStorm:


Better judgment says B, but obsessive sat. loop watching has me leaning to A.
thw answer is A very likely we have TD 2 and maybe TD 3 with in the hour
Member Since: July 14, 2009 Posts: 0 Comments: 3022
2721. IKE
Quoting tharpgomex:
Hey Ike....lived in Defuiak during Opal....what a mess!


Yes it was. I'm up on Lake Holley. Branches...everywhere from Opal.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting SavannahStorm:




Whoa, a hurricane means no school? Gnarly. I bet it brings on some like, tasty waves, too. Righteous.

Roflmao!!!
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Quoting extreme236:


02L was classified but 90L has yet to be renumbered.
yup.
I agree Mobilegirl. And am wanting some perspectives about development? Anyone?
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Quoting DM21Altestic:
POLL


A) 90L WILL be a TD at 11 PM.
B) 90L will be a TD tomorrow.
C) 90L will be a TD Sunday.
Z) 90L will never be a TD.


Better judgment says B, but obsessive sat. loop watching has me leaning to A.
Member Since: Posts: Comments:
2716. 7544
canesrule1 2:05 AM GMT on August 15, 2009
Quoting louisianaboy444:
I truely believe both will be TDs at 11
agreed

same here
Member Since: May 6, 2007 Posts: 0 Comments: 6857
Quoting canesrule1:
A, it already was renumbered so all the other choices are useless, lol.



TD 2 was re-designated, 90L was never renumbered, not yet.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Patrap:
Irony always wins..

Mr. Bill PSA from 2003-4 from Creator ,He's from Louisiana.

In this public service announcement created before Katrina, Mr. Bill of SNL fame demonstrates the dangers of a hurricane hitting New Orleans.






OMG pat. That is so not funny, but I can't stop laughing....
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2713. Patrap
Quoting rareaire:
Pat you didnt go to the game?


Nope..Pre-season Like a Blind date after the first quarter
Member Since: July 3, 2005 Posts: 426 Comments: 128667
Quoting TampaSpin:
TD2 is moving faster than 90L and also TD2 is mow moving WSW heading toward the Caribbean as i have forecasted.
but how come all the models forecast a SFLA hit?
Quoting canesrule1:
A, it already was renumbered so all the other choices are useless, lol.


02L was classified but 90L has yet to be renumbered.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2709. snotly
Quoting Weather456:


B

D?
Member Since: Posts: Comments:
I'm sure most people on here could do a better job at presenting the weather than the people on TWC. All that TWC is in it for now is show-boating and trying to impress their audience.

Example: Storm Master G!! Seriously, WTF???

Whatever happened to just giving the weather and how it is and leaving it at that?

Nonetheless, I never listen to TWC when it comes to tropical weather. I get much better info on this blog and just doing research myself.
Member Since: Posts: Comments:
Quoting Weather456:


B
its already renumbered it has to be a TD at 11.
Quoting louisianaboy444:
I truely believe both will be TDs at 11


Respectfully disagree.
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Quoting DestinJeff:


destin here. Ike and 69Viking are two close by I can think of

i am in defuniak springs(mossy head)
Member Since: July 7, 2008 Posts: 0 Comments: 473
2704. Patrap
NexSat Viz to Night IR loop,90L
Member Since: July 3, 2005 Posts: 426 Comments: 128667
TD2 is moving faster than 90L and also TD2 is mow moving WSW heading toward the Caribbean as i have forecasted.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Quoting DM21Altestic:
POLL


A) 90L WILL be a TD at 11 PM.
B) 90L will be a TD tomorrow.
C) 90L will be a TD Sunday.
Z) 90L will never be a TD.
A, it already was renumbered so all the other choices are useless, lol.
Quoting DM21Altestic:
POLL


A) 90L WILL be a TD at 11 PM.
B) 90L will be a TD tomorrow.
C) 90L will be a TD Sunday.
Z) 90L will never be a TD.


B
Member Since: July 24, 2005 Posts: 407 Comments: 19076
TD 2 looking very impressive now. Could be Ana tonight or in the morning ...
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Quoting louisianaboy444:
I truely believe both will be TDs at 11
agreed
Both systems keep on growing.. Maybe Tropical Storms Ana and Bill tomorrow night at this time..

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Quoting futuremet:


Ike, if that is true, then your forecast very close was very close.

ike has been very level headed and i respect his opinions
Member Since: July 7, 2008 Posts: 0 Comments: 473
Pat you didnt go to the game?
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I truely believe both will be TDs at 11
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Quoting extreme236:
Central convection with 90L has increased markedly in the past few hours since those dvorak estimates. I believe we would see a 2.0 right now.
we only have to wait 40 minutes to see.
Quoting Weather456:
Nothing is working this year

I found out where 95L was.....




How Jovial :)
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TD2 and 90L

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2689. Patrap
SQUAWK One,WAIT One.....

Expect a New Message at the 11pm from the NHC.

Then you'll know.


Member Since: July 3, 2005 Posts: 426 Comments: 128667
Quoting jipmg:


I really really doubt that.. its wayy too small for it to affect TD 3 in any "significant" manner


I respectfully disagree with you!
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Central convection with 90L has increased markedly in the past few hours since those dvorak estimates. I believe we would see a 2.0 right now.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting IKE:


Close....Defuniak Springs,FL.

Paul Goodloe said we may have a TS at 11.


Ike, if that is true, then your forecast very close was very close.
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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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