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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with the exposed centre, this will allow ANA to continue on a west track
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Quoting cycloone:
Hurricane Charley in 2004 went from a cat1 to a cat4 overnight.

Don't give Bill any ideas lol


Wilma broke that record.
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Quoting Drakoen:


Agree. No reason to downgrade to a TD
nope, convection actually has rised in the past 3 hours, should have 45-50 MPH, imo.
5031. divdog
Quoting kingofhurricanes:
I LIVE IN PALM BEACH...... AM I GOING TO GET A STORM THIS YEAR????????


of course you are geeeeeeeeeeeeeeeeeeeeeeez
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Quoting TerraNova:


Then we've had a depression for just over 40 minutes and they'll initiate advisories at 11:00.


yea
Member Since: July 24, 2005 Posts: 407 Comments: 19076
5029. tea3781
Our local meteorologist here said that even though Anna has lost some of its convection. Its banding features have grown which shows signs of strengthning in the future.
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Quoting dcoaster:
Ana seems to be staying due west, right on the projected path.



I'm giving your post one of my very rare, and highly coveted "+"s. :)
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morning everyone. any thoughts on the wave near cuba? is it something to keep an eye on?
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5000 comments wow I don't think I've seen that many comments on one entry in the two years I've been here.
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kman...just that convection of crap down there below the keys...there is a spin and granted it does look to be moving west but alot of the models have something coming out of it and heading north towards the panahandle...just curious is all...but of course like everything else...subject to change..."A LOT"
Member Since: June 3, 2008 Posts: 0 Comments: 1924
Jeff is waiting till the 11 O'clock comes out, imo.
5022. Drakoen
Quoting extreme236:
I imagine Ana will look better again later this afternoon and evening.


Agree. No reason to downgrade to a TD
Member Since: October 28, 2006 Posts: 57 Comments: 29942
Quoting WeatherStudent:


Dying is more like it. Anyways, all of my attention is now solemnly focused on TD3.
I would not say she is dying, but currently struggling...I would not take my eye off her and ignore her. There are just as good of a chance she could quickly spin up and be at our doorstep as passing south into the Caribbean or turning north. If she is able to maintain through this rugh patch, formation to a cane is not out of the question.
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5020. Drakoen
Quoting Melagoo:
I think this Blog is ready to go into the archives now .... start a new one


lol I think this is the most pages the blog has ever had
Member Since: October 28, 2006 Posts: 57 Comments: 29942
the sat presetation of 90L that of a tropical storm. at 11 am tropical storm BILL will be christened
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Quoting dcoaster:
Ana seems to be staying due west, right on the projected path.



That's a GREAT overlay! Thank you for posting that!

Feel free to update that as regularly as you may be inclined to! :)
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Quoting cycloone:
Hurricane Charley in 2004 went from a cat1 to a cat4 overnight.

Don't give Bill any ideas lol
LMAO
5016. Melagoo
I think this Blog is ready to go into the archives now .... start a new one
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5015. CJ5
Quoting extreme236:
I imagine Ana will look better again later this afternoon and evening.


I suspect the same, it has looked its worse this time each of the last three mornings.
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Quoting Funkadelic:
Will 90L Be a tropical storm, or a depression at 11am?

Poll:

A: Tropical Storm

B: Tropical Depression

AAAAAAA is should be a TS
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5013. 996tt
Anna's center looks like it may be exposing. Any updated on the Key West wave. Even surf reports are not indicating any swell this week in Pensacola. Be nice if the Key West low would throw a swell this way.
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Quoting stillwaiting:
looks like we should have ana by the 11am tomorrow,IMO,a compact system...but that might change in time....



looky,looky here....well what do ya know???...
this set up is reminding me of 04'...bad set up for FL and the eastern half of the GOM,IMO
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Quoting kachina:


LOL - that's like saying California is in great danger of another Earthquake or New York is in great danger of another blizzard. Seriously....do they have monkeys working over there at TWC?
LMAO, yup
Quoting Weather456:


been there since 9:30


Then we've had a depression for just over 40 minutes and they'll initiate advisories at 11:00.
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Hurricane Charley in 2004 went from a cat1 to a cat4 overnight.

Don't give Bill any ideas lol
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5008. CJ5
Quoting WeatherStudent:


Dying is more like it. Anyways, all of my attention is now solemnly focused on TD3.


Dying would be inaccurate.
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5007. kachina
Quoting canesrule1:
I was watching the TWC, and they said "South Florida is in great danger of another Hurricane", im like WTF? lol


LOL - that's like saying California is in great danger of another Earthquake or New York is in great danger of another blizzard. Seriously....do they have monkeys working over there at TWC?
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Quoting extreme236:


No?

DVTS, CI, , 1170N, 3290W, , 3, 30, 2, TAFB,

Ana was 2.5 from both.


SAB TEB VI 3 2025 /////
TAFB GR VI 5 2525 /////
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I imagine Ana will look better again later this afternoon and evening.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Hurricane Charley in 2004 went from a cat1 to a cat4 overnight.
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Trying again?
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Quoting Funkadelic:
Will 90L Be a tropical storm, or a depression at 11am?

Poll:

A: Tropical Storm

B: Tropical Depression


A
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Marine Weather Discussion
--------------------------------------------------------------------------------


000
AGXX40 KNHC 150656
MIMATS

MARINE WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
300 AM EDT SAT AUG 15 2009

MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA
AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W.

WINDS ARE GENERALLY LIGHT ACROSS THE GULF OF MEXICO. HOWEVER
WINDS WILL START TO INCREASE OVER THE EASTERN GULF AS TROUGH
WHICH WAS THE NORTHERN END OF A TROPICAL WAVE MOVES INTO THE
AREA. THE TROUGH WILL MOVE ACROSS THE EASTERN AND MIDDLE GULF
TODAY AND SUN THEN INTO THE NW GULF MON AND INLAND TUE. THE
STRONGEST WINDS WILL BE OVER THE SE GULF THEN SPREAD W INTO THE
SW GULF BY MID WEEK.


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Coming up on the Weather Underground Blog...Ana Exposed...a shocking story of you won't want to miss.
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A likely thunderstorm event is what it is now.

What will it be tomorrow?
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NHC will be conservative: B
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Quoting TerraNova:
Tropical Depression 3 just popped up on NOAA's FTP server.

invest_RENUMBER_al902009_al032009.ren

Winds = 30 kts
MSLP = 1006 mb
Location = 11.5N, 33.3W


been there since 9:30
Member Since: July 24, 2005 Posts: 407 Comments: 19076
I LIVE IN PALM BEACH...... AM I GOING TO GET A STORM THIS YEAR?????????
Member Since: Posts: Comments:
Ana seems to be staying due west, right on the projected path.

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5000
Quoting extreme236:
Convection trying to cover the center of Ana in the 13:45 Navy image.

I agree looking at AVN ir loop convection is moving over COC
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Quoting Funkadelic:
Will 90L Be a tropical storm, or a depression at 11am?

Poll:

A: Tropical Storm

B: Tropical Depression
A
Quoting Funkadelic:
Will 90L Be a tropical storm, or a depression at 11am?

Poll:

A: Tropical Storm

B: Tropical Depression


B
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Did I Hit 5000?
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Quoting Funkadelic:
Will 90L Be a tropical storm, or a depression at 11am?

Poll:

A: Tropical Storm

B: Tropical Depression
A
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On sept 12, 2009 will be exactly 30 years since Frederic hit.
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Tropical Depression 3 just popped up on NOAA's FTP server.

invest_RENUMBER_al902009_al032009.ren

Winds = 30 kts
MSLP = 1006 mb
Location = 11.5N, 33.3W
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4964. ok, i was wondering if the shear was going to start ripping it apart again
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B. Final answer for $1,000
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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.