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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90L is weaker on this run.. probably because it didn't develop yesterday (Friday).

Member Since: July 1, 2008 Posts: 13 Comments: 7340
Wow Weather456, this could be a very close call with htitting Florida or sideswiping it.
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As soon as 90L reaches the islands, it shifts west under a building ridge

Member Since: July 24, 2005 Posts: 407 Comments: 19076
where are the models taking 90L and soon but not yet reborn TD 2?
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3530. Patrap
NEXRAD Radar
Miami, Storm Relative Mean Radial Velocity 0.50 Degree Elevation Range 124 NMI


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Conditions are right in GOM for a system to ramp up quickly. Low shear an hot A water.
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Member Since: July 24, 2005 Posts: 407 Comments: 19076
I THINK the center of 90L may be relocating a bit more west towards the convection. I might be wrong.
Member Since: July 1, 2008 Posts: 13 Comments: 7340
Quoting CaicosRetiredSailor:
if

big ...IF I read this right the 00z GFS here shows exTD2 right on Guadeloupe at 120 hours...





Pleas correct me if I am wrong here.


Model shown at

http://moe.met.fsu.edu/tcgengifs/
CRS


Thats is 90L and a new system behing it, TD2 is remaind RIP according GFS.
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Quoting stormsurge39:
Does anyone know if that is a surface low trying to form south of Cuba?


ULL
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Quoting atmoaggie:
hey nrt, I thought we had satellite meneuvers last night. Meteosat doing it now?

For example:

Edited: Answer myself: Nope, here is a plot from 03:00 utc.
Maybe, it is over an hour old plot in a supposedly near-realtime page.


Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting 7544:
oh we may have a spin in our cuba wave
I'm looking at the samething a spin South of Cuba,the models are showing some type of tropical development from this wave aroung east South Florida.
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K, I'm gonna head off to bed now, I'm sure everything that is here now will be there in 8 hours. Everyone GOOD NIGHT!!!!

-CanesRule1
Quoting StormFreakyisher:

Maybe they didn't want to update at 11p because they knew it became a TD2 again and didn't want to feel shamed that they took it off yesterday as a low. They are waiting till it weakens so at 2am they can still leave it as a circle and not TD.Lol joking


Quoting mikatnight:
"This product is updated at approximately 2 AM, 8 AM, 2 PM, and 8 PM EDT from June 1 to November 30. Special outlooks may be issued as conditions warrant."



2am according to the NHC unless a special advisory is warranted.
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The 00Z GFS is running.. up to 78 hours right now.
Member Since: July 1, 2008 Posts: 13 Comments: 7340
if

big ...IF I read this right the 00z GFS here shows exTD2 right on Guadeloupe at 120 hours...





Please correct me if I am reading this wrong here.


Model shown at

http://moe.met.fsu.edu/tcgengifs/

CRS


[edit] OOPS I see legend at top says its the 1800 Z run ... sorry
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3518. Patrap
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3516. KEEPEROFTHEGATE (Mod)
Quoting Weather456:
impressive

right on cue 456 if everything plays out as iam expecting 90l will be 03l tomorrow afternoon

former 02l/INV91L re-borned one to watch as its closer at the moment

and a nice turning movin into gom in the am

lots to watch

have a plan
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Does anyone know if that is a surface low trying to form south of Cuba?
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Quoting weatherboykris:
GFS ensembles not as tightly clustered. The main group nudged a bit north and their are now a few southern outliers. The overall average seems to have shifted north, IMO.



Hugo
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3513. 7544
oh we may have a spin in our cuba wave
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Quoting canesrule1:
no update at 11 maybe at 2?

Maybe they didn't want to update at 11p because they knew it became a TD2 again and didn't want to feel shamed that they took it off yesterday as a low. They are waiting till it weakens so at 2am they can still leave it as a circle and not TD.Lol joking
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3510. Patrap
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Quoting sammywammybamy:
Everyone in Tropics Chat

My browser says bad things about that place and boots me out.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
"This product is updated at approximately 2 AM, 8 AM, 2 PM, and 8 PM EDT from June 1 to November 30. Special outlooks may be issued as conditions warrant."

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00z Now develops a new wave east of 90L into a TC in 72 hrs.
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3506. AndyN
18Z GFS valid until midnight on 8/25 is kinda scary. I realize this is voodoo land: http://bit.ly/19vv3h
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Quoting sfla82:
Now that I see the latest ensemble models for 90L I feel much better here in S. Fla!!! wooohhhh! This wave will bring us much needed rain! ex TD2 shouldn't be a threat so it seems for now S. Fla has dodged another bullet! September is right around the corner though! We will see!
wouldn't start to breathe so easy quite yet...NO ONE knows what is going to happen yet to be able tomake a statement like that....
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Quoting sammywammybamy:
Everyone in Tropics Chat
lets go!!
I'm going to bed. Those storms will probably still be there when I wake up.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting sfla82:
Now that I see the latest ensemble models for 90L I feel much better here in S. Fla!!! wooohhhh! This wave will bring us much needed rain! ex TD2 shouldn't be a threat so it seems for now S. Fla has dodged another bullet! September is right around the corner though! We will see!



if anything the new ensemble models shifted north from previous run so how would that make you feel better lol
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Quoting sammywammybamy:
The Typical WU Blogger Now has a Question to Ask themselves

A. Do i Stay and Wait for 1AM OR 2AM
B. Ahhh Who Cares .. Me Sleepy
C. Puts the Tv On and Waits
D. Slams His head onto the Computer

What Would you Chose For Tonight?

T: press alt-f4 repeatedly and call it a night.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting canesrule1:
looks like a TS, remember DMAX just started, could be the reason for the organization?


that could be 1 reason
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting sfla82:
Now that I see the latest ensemble models for 90L I feel much better here in S. Fla!!! wooohhhh! This wave will bring us much needed rain! ex TD2 shouldn't be a threat so it seems for now S. Fla has dodged another bullet! September is right around the corner though! We will see!


South Florida is as much in the bullseye as any area of eastern conus at this point, regardless of the models.
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E. All of the Above.
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Quoting JohnnyMandeville:
Just came in to the blog, how close should we, on the gulf coast, be paying attention to the weather coming between FL and Cuba?

I haven't been at all impressed with it.
Cheers,
-atmoaggieCovington
Member Since: August 16, 2007 Posts: 6 Comments: 12461
E. LOL! Take the puppy out for a walk and wait :P
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hey nrt, I thought we had satellite meneuvers last night. Meteosat doing it now?

For example:
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting CaneWarning:


I would think a northern shift puts Florida more at danger, while a southern shift puts the rest of the gulf at more danger.


I don't know. If it goes through Florida, it still ends up in the Gulf
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Latest from Atlantic Beach, NC courtesy of ablivesurf.com:

Afternoon Report Flat as I've seen it in months. Looks really cool at the beach though. The silver ocean blends right in with the horizon. Check back tomorrow for updates

Temp is 79, which is 26C. Has been as warm as 82 recently.
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Quoting Stoopid1:
NHC is doing 8p.m. and 2a.m. updates now since there are no organized systems. Once a TD forms they do 11 and 5 updates.


Thats not true nor accurate......the 11 and 5 are the full updates and the 2 and 8 are the intermediate updates.....
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Quoting Weather456:
impressive

looks like a TS, remember DMAX just started, could be the reason for the organization?
E. Drink another beer and wait for WS to make another one of his classic comments..
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3487. sfla82
Now that I see the latest ensemble models for 90L I feel much better here in S. Fla!!! wooohhhh! This wave will bring us much needed rain! ex TD2 shouldn't be a threat so it seems for now S. Fla has dodged another bullet! September is right around the corner though! We will see!
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3486. Patrap
Quoting KATRINABILOXIGIRL:
thanks Pat...love all your little sayings..cute...and hope you enjoyed the game


Game was a good break from the frays out in the Big Pond for sho..
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Quoting sammywammybamy:
The Typical WU Blogger Now has a Question to Ask themselves

A. Do i Stay and Wait for 1AM OR 2AM
B. Ahhh Who Cares .. Me Sleepy
C. Puts the Tv On and Waits
D. Slams His head onto the Computer

What Would you Chose For Tonight?
A
3484. Patrap
Quoting StormW:


Looks that way my friend. I'll probaly post sometime tomorrow afternoon.

Thank you and those who joined in the show last night.


Shucks StormW,.thats was a good experience for many as everyone enjoyed it all Im sure.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.