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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2584. mkmand
Quoting extreme236:
Funny how we all thought TD 2 would become Ana and 90L would be Bill. Then TD2 became a remnant low then 90L was Ana. And now were back where we started.

I know thats funny!
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2583. hahaguy
Quoting IKE:


Is he incapable of knowing that?


I'd say so.
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2581. 7544
Quoting GeoffreyWPB:
I see we have 91L up on the Navy site.


maybe thats the blob n of cuba now ?
Member Since: May 6, 2007 Posts: 0 Comments: 6730
Quoting Weather456:
Frankly both 90L and TD 2 looks impressive, which one will fizzle will be interesting.


Hmm, so you think one of them will fizzle now? Interesting.
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CELEBRATE!!!
0,0,0 CONDITION STILL EXISTS!!!
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2578. jipmg
Quoting sammywammybamy:


If this does become ana in the next 24-48 hours..

What are we Looking at Intensity as it Nears S.FLA?

I Know you Cannot Predicte the Future..But your general thoughts on strength?


I think my local mets will talk about it at the 11pm brodcast...


models indicate either a strong wave or a strong TS/ CAT 1 hurricane.. I say things can change and I expect them too intensity wise
2577. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 127803
Quoting extreme236:
Here we go:

AL, 02, 2009081500, , BEST, 0, 145N, 448W, 25, 1007, TD


Again.. lets see if this time it goes for Ana.
Serious issue here if the whole time 90L was infact destined to become 'Bill'.
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2575. IKE
Quoting hahaguy:


Nobody knows yet .


Is he incapable of knowing that?
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I see we have 91L up on the Navy site???
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Quoting Stormchaser2007:



The easterly shear will limit the convection from fully engulfing the LLC. Once that happens ill be impressed.


It might happen tonight.. You never know what these systems can do.
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Funny how we all thought TD 2 would become Ana and 90L would be Bill. Then TD2 became a remnant low then 90L was Ana. And now were back where we started.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Frankly both 90L and TD 2 looks impressive, which one will fizzle will be interesting.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting hurricane23:
If extd2 strengthens significantly it could help to turn Invest 90 to the north quicker than thought right now.


Not really, because they're father away and ex-TD2 is much smaller than that huge circulation behind it.
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Quoting CandiBarr:


OO i know where abouts! the bay was new find though. we are pretty close. tallow creek area. i'm glad to hear you didnt have any damage.

You got a fair bit of elevation over there, too, right? Maybe not quite as much topography...but some.
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Quoting Stormchaser2007:
Not impressed.



That burst right near/over the center makes it look more impressive than when it was exposed earlier.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting gbreezegirl:
Well here in the panhandle we have had quite enough for a lifetime. I don't want to even think about comparing any of this to 2004 season.


Ditto gbreezegirl! With Ivan and Dennis I have had enough!
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Quoting reedzone:


I am starting to be impressed, this satellite is faster then the NHC..



Notice the blow up of convection, expanding near the center.



The easterly shear will limit the convection from fully engulfing the LLC. Once that happens ill be impressed.
Member Since: June 9, 2007 Posts: 4 Comments: 15864
Maybe 90L is "Bill the African Wave"....
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On the navy site is td2 getting renamed at 91L?
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Quoting extreme236:
Here we go:

AL, 02, 2009081500, , BEST, 0, 145N, 448W, 25, 1007, TD,


WOOOOHOOOOO!!!
2557. jipmg
oh oh Bill is looking like it might happen by tomorrow morning
2556. aquak9
what are ya saying, extreme...

(sorry gotta have a thread of hope here)
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Here we go:

AL, 02, 2009081500, , BEST, 0, 145N, 448W, 25, 1007, TD


I should go officiate the Saints game...I sure made that call
Member Since: August 29, 2006 Posts: 22 Comments: 1345
2553. hahaguy
Quoting Stormchaser2007:
Its possible that we could have a TD at 11pm from ExTD2. 90L should be better organized in 24-36 hours.


Looks that way.
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2552. Patrap
Now that TD-3 has formed officially,a Lot more ASSETs will now come into play as we have 2 Cyclones forming and the resources will become more wide,..and focused.



Member Since: July 3, 2005 Posts: 423 Comments: 127803
Quoting canesrule1:
ROFLMAO, i love "im on a boat" lol


I'm on a boat.
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Quoting extreme236:
Here we go:

AL, 02, 2009081500, , BEST, 0, 145N, 448W, 25, 1007, TD


We can all sleep in peace now...unless your in the swath of doom.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Quoting Stormchaser2007:
Not impressed.



I am starting to be impressed, this satellite is faster then the NHC..


Notice the blow up of convection, expanding near the center.
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Its possible that we could have a TD at 11pm from ExTD2. 90L should be better organized in 24-36 hours.
Member Since: June 9, 2007 Posts: 4 Comments: 15864
Quoting extreme236:
Here we go:

AL, 02, 2009081500, , BEST, 0, 145N, 448W, 25, 1007, TD,


Sweet!
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2546. jipmg
so its confirmed we now have TD 2 again, we might even have an ANA at 11.. this thing is getting strong fast
Quoting sammywammybamy:


TampaSpin... Is it me or is it Looking like ana?



No doubt we have ANA very soon.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
2543. jdjnola
Quoting Patrap:
Hurricane Preparation Entry


Thanks Patrap. I suggest everyone living along the coast at a minimum collect empty bottles of water to fill up with fresh water in case of an approaching storm (I think the guideline is something like a gallon per person per day), plus canned foods and medications.
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Here we go:

AL, 02, 2009081500, , BEST, 0, 145N, 448W, 25, 1007, TD
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Not impressed.

Member Since: June 9, 2007 Posts: 4 Comments: 15864
Quoting sammywammybamy:


TampaSpin... Is it me or is it Looking like ana?

i say it does look like ana!
Quoting SavannahStorm:


It was also a 80mph hurricane that pulled a Cat. 5 storm surge with it.


Not when it hit S. Florida.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
2537. jipmg
Quoting Stormchaser2007:

I was saying in terms of affecting 90Ls track lol.


oh yea I agree, that and the fact its so small
Quoting Stormchaser2007:
Somehow the SAL found a way to affect 90L. It always does....



It would appear so, but I think the easterlies are having more of an effect than the SAL as 90L remains large and the convection remains strong.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting louisianaboy444:
it did,


2-3 days ago. lol


Lol ok wise guy...I will stick my neck out here and say that TD2 is already back but the NHC hasn't made it official yet...90L has also started building some convection near its center


lol just playing
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting jipmg:


Katrina did so much damage and it was an 80MPH hurricane.


It was also a 80mph hurricane that pulled a Cat. 5 storm surge with it.
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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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