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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Atlantic is boiling!
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we have Anna now
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3882. Patrap
GOES-12 Low Cloud Product
Member Since: July 3, 2005 Posts: 420 Comments: 127530
3881. KEEPEROFTHEGATE (Mod)
latest image 615 utc



02L/TS/ANA
MARK
14.1N46.3W
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Quoting jipmg:
when the next satelite comes in im out


procrastination is a sin :)
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3879. jipmg
when the next satelite comes in im out
Yeap! we will have many hours of intense expecting! Like the friend said, there's be a new TD and a named storm at 5-8 am.
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3877. KEEPEROFTHEGATE (Mod)
still awake pat i see
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Good evening guys and girls, seems like a lively night for the Atlantic. Cheers
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3875. Patrap
GOES WV Loop of Tropical Basin
Member Since: July 3, 2005 Posts: 420 Comments: 127530
3873. Patrap
Member Since: July 3, 2005 Posts: 420 Comments: 127530
Quoting reedzone:
I have to agree with some people, TD2 might be organizing a bit further then it was supposed to.. A very small buzzsaw look to it..



They have NOAA 43 and 49 in barbados right now if they need them.
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TD 2 hiting caribbean in 3-4 days and turning northwest to the east coast....OmG! The convection is really defined in both!
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Oh right, and the long-term GFS sends 90L toward Talahassee in the Gulf and the system behind it toward the Antillies and the Northeast of CONUS.
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3867. KEEPEROFTHEGATE (Mod)
Two

2009-08-15 00:00 -- 2009-08-15 06:30
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Quoting KEEPEROFTHEGATE:
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 15 AUG 2009 Time : 041500 UTC
Lat : 14:35:46 N Lon : 45:38:40 W


CI# /Pressure/ Vmax
3.4 / 995.2mb/ 53.0kt


Final T# Adj T# Raw T#
(3hr avg)
3.4 3.5 3.5

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : -58.3C Cloud Region Temp : -46.4C

Scene Type : CURVED BAND with 0.75 ARC in LT GRAY

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

****************************************************


I dont trust the DVORAK techinique because it should of been declared Ana the first time.
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90L will be Tropical Depression 3 by 5 a.m., and at this rate, it might be a named storm by 11 a.m. WOW, very impressive and looks like convection organizing around the circulation at 33W and 13N. I might be wrong though, but the system is getting more symmetrical.

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3864. jipmg
so the 995MB presussre is confirmed?
It's incredible see how in less than 24 hours a system that much people think that have no chance to develope again, suddenly regenerates. Models are constant. For me is matter of another recon to declares TD2 in Anna. My opinion after lived many hurricanes and storm in my live I thing that is very serious high possibilities to threat the Antilles. Have been 11 years since George, the TD2 would be like Jeanne in 2004, but the 90l looks more impressive and models put it over PR and leeser antilles...No more Antlantic Sleeping Beauty
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3862. KEEPEROFTHEGATE (Mod)
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 15 AUG 2009 Time : 041500 UTC
Lat : 14:35:46 N Lon : 45:38:40 W


CI# /Pressure/ Vmax
3.4 / 995.2mb/ 53.0kt


Final T# Adj T# Raw T#
(3hr avg)
3.4 3.5 3.5

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : -58.3C Cloud Region Temp : -46.4C

Scene Type : CURVED BAND with 0.75 ARC in LT GRAY

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

****************************************************
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I have to agree with some people, TD2 might be organizing a bit further then it was supposed to.. A very small buzzsaw look to it..

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Quoting jipmg:


based on what?

Based on shortwave IR. It looks like the spin is right on the eastern edge of that round blob.
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3859. Patrap
Member Since: July 3, 2005 Posts: 420 Comments: 127530
Quoting FloridaTigers:
I think we'll have Ana by 5AM


Im going to wait until the QuickScat show 35 knot winds...until then I dont expect them to update it into a tropical storm till that happens. There was no quickscat last hour b/c it was the same. They only change it every hour when it's different.
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Quoting jipmg:


link!

Link (Phail if we don't all know that one)
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3856. Patrap
Member Since: July 3, 2005 Posts: 420 Comments: 127530
3855. jipmg
Quoting AstroHurricane001:
Holy crap, CMC sends TD 2 directly towards NOLA, and 90L toward Bermuda! HWRF also follows suit by sending a major hurricane into the Gulf. Gonna be an interesting rest of the month.


link!
Holy crap, CMC sends TD 2 directly towards NOLA, and 90L toward Bermuda! HWRF also follows suit by sending a major hurricane into the Gulf. Gonna be an interesting rest of the month.
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3853. jipmg
Quoting howarjo1943:
I think the circulation center of TD 2 is still partially exposed to the east of that blob which may mean it's weaker than the Dvorak #. Not sure though.


based on what?
Quoting KEEPEROFTHEGATE:


Where did you find that? Link plz?
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Quoting jipmg:
yea so do I, and TD 3


I believe we will have Ana and Bill later today.
Member Since: July 15, 2006 Posts: 17 Comments: 10159
I think the circulation center of TD 2 is still partially exposed to the east of that blob which may mean it's weaker than the Dvorak #. Not sure though.
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3848. jipmg
yea so do I, and TD 3
I think we'll have Ana by 5AM
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alright, I'm off for a few hours sleep.gn
Member Since: December 9, 2006 Posts: 125 Comments: 11346
Quoting jipmg:


can you post it here


Sure! It's right here....

TD 2: http://manati.orbit.nesdis.noaa.gov/dataimages21/cur/zooms/WMBas26.png
(North of it...3 barbs = 30 knots = 35 mph)

Low...http://manati.orbit.nesdis.noaa.gov/dataimages21/cur/zooms/WMBas32.png
(North of it....2 barbs...= 20 knots = 23 mph)
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3844. 7544
after black we have to see waht the cuba blob will look like 40 min to go
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3843. KEEPEROFTHEGATE (Mod)
nite tim
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3842. 7544
Quoting TampaSpin:
Nite everyone..


nite tampa
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Nite everyone..
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3839. KEEPEROFTHEGATE (Mod)
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Quoting Drakoen:


Link


ty...do u have the link to the text model output for the BAMs?
Member Since: December 9, 2006 Posts: 125 Comments: 11346
Are the #'s above that someone posted (the 995mb reading) correct? I'm guessing that was one of the satellite estimates?
Member Since: July 15, 2006 Posts: 17 Comments: 10159
3836. jipmg
Quoting WeafhermanNimmy:
QuickScat shows winds with TD # 2 up to 30 knots...QuickScat on Invest 90L doesnt have closed low but it's very close! Max wind w/Invest 90L is 20 knots (20 mph)


can you post it here
QuickScat shows winds with TD # 2 up to 30 knots...QuickScat on Invest 90L doesnt have closed low but it's very close! Max wind w/Invest 90L is 20 knots (20 mph)
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3834. Drakoen
Quoting weatherboykris:


Link?


Link
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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.