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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Quoting ackee:
if TD#2does come back where do u think it will track ?

caribbean or the northern caribbean islands
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Good thing with them going to sample Ex TD2, they will have good upper air data into the models for 90L.
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Quoting RitaEvac:
I've noticed Home Depot/Lowes have batteries all over the store, I thought about buying some, but was like.....nahhhhhhh

Their prices are remarkably good, too. (I just picked up an extra pack, just in case)
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Wow 90L looks better and big!

Member Since: July 31, 2006 Posts: 19 Comments: 1558
Link UPDATED BLOG,my best analysis forcast track for 90l/and more.
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Quoting RitaEvac:


Florida right dead in the weakness

Yup
Member Since: October 28, 2006 Posts: 57 Comments: 29928
127. IKE
116 and 117.

I think he's not alone on this blog...wanting a hurricane, or thinking they do.

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Off to work.. back in about 60 to see what I missed... my guess would be about 400 posts.

Member Since: October 1, 2007 Posts: 81 Comments: 26511
124. ackee
if TD#2does come back where do u think it will track ?
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I haven't seen this much model consensus so far out in a very long time!
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Good Morning All !!!
Thanks for the update.
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Quoting Drakoen:
Long range CMC has a South Florida hit the possibly into the GOM or up the state. Definitely an interesting and possible track:
i think it might curve over Florida but i think this track is very possible.
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Quoting Drakoen:
Long range CMC has a South Florida hit the possibly into the GOM or up the state. Definitely an interesting and possible track:


Florida right dead in the weakness
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Quoting Category5hitsNewYork:
I want to see a hurricane hit so badly. What are the chances I see a hurricane from AUG 26TH TO AUG 31ST WHEN I TRAVEL TO FLORIDA!!!! SORRY if this question seems nihilistic


Take a 2000mile boat ride to the East in a 12ft john boat and wait at the 12N 50W line and you can see one....But hurry in don't want you to miss it.....OMG!
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116. CJ5
Quoting Category5hitsNewYork:
I want to see a hurricane hit so badly. What are the chances I see a hurricane from AUG 26TH TO AUG 31ST WHEN I TRAVEL TO FLORIDA!!!!


I can quarantee if you go ahead now and rent a boat and head SW you will find what you are looking for. You could even give us live reports as long as you are afloat.
Member Since: July 4, 2007 Posts: 0 Comments: 1755
Good Evening / Morning all.
Just listening to the podcast of today's Barometer Bob's show.
Member Since: September 30, 2007 Posts: 9 Comments: 15932
113. IKE
Quoting wunderkidcayman:

both ex-TD2 and 90l(pre-td3) is in the clear from SAL


I remember when Felicia was a strong hurricane in the east-Pac, I looked at the SAL chart on it. It was similar to what is north of 90L.
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Whilst never wanting a direct hit (Luis in 95 put paid to that silly wish forever) like everyone else here Im fascinated by tropical weather.

However, I am particularly anxious that 90L doesnt threaten the Northern Leewards (St Martin/Maarten ) as a hurricane next week as we are counting down the days for our vacation to New York City...and our departure is currently scheduled to coincide with its arrival!

A hurricane warning is enough to close Juliana Airport...

So kindly curve off to the North, 90L

Dan
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Quoting PanhandleChuck:
IF... TD2 makes a come back, will it still have the TD2 designation, or will it be something else


The low level center remained so it would still be TD2.
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Long range CMC has a South Florida hit the possibly into the GOM or up the state. Definitely an interesting and possible track:
Member Since: October 28, 2006 Posts: 57 Comments: 29928
Quoting IKE:
1200UTC SAL....


both ex-TD2 and 90l(pre-td3) is in the clear from SAL
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If it stays weak, then it will continue west. After it miss being pulled up then its game on.
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IF... TD2 makes a come back, will it still have the TD2 designation, or will it be something else
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106. CJ5
Well things have finally started to heat up. I see a good chance TD2 could come back today and 90L becoming a TD. It is going to be a long week coming up for many. Prepare and check everything now.
Member Since: July 4, 2007 Posts: 0 Comments: 1755
Quoting Drakoen:


Yea. The trough is stuck in the plains allow the ridge to build towards the east coast


It may shift back and forth for a while from day to day on the models...
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103. eddye
sal not that bad
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Quoting mobilegirl81:
Given a tight model concensus and a consistent steering pattern, might be a good idea to check out any supplies one may need.



I would hedge 90% on a tropical cyclone between St. Lucia and the Virgin Islands 5 days from now. Steering will not change enough in that time period to allow any different. The only exception, as Dr. Masters pointed out, is if the storm moves slower like the ECMWF.

Ships has a 107mph cyclone in 5 days, intensifying quite rapidly.
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101. IKE
1200UTC SAL....

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Quoting IKE:
TD2 is firing up...could be a Caribbean runner.

Flattened out and shifted back west. Not good for avoiding the USA.


Yea. The trough is stuck in the plains allow the ridge to build towards the east coast
Member Since: October 28, 2006 Posts: 57 Comments: 29928
Nice looking cooler! We are going out tomo morning. High tide is right at sunrise. Should be a great day.


Quoting mobilegirl81:
Looks like we cant go fishing this weekend.
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Quoting mobilegirl81:
TD2 trying to come back?

well yes
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96. IKE
Quoting BenBIogger:
8 to 10 DAY 500MB MEAN

0z (from today)


12z (from yesterday)


Flattened out and shifted back west some. Not good for avoiding the USA.
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Morning All,
I know it is way to early to be sure of anything but this island( Turks and Caicos) can in no way face another hurricane...
and evacutaion here is a costly affair... last year for IKE came to quite a few thousand $$$$ for us. Just for a few days.
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Quoting extreme236:
The small area of convection with ex-TD2 has expanded a bit further to the east, and now covers most of the circulation center.


I agreed... it has been doing well at increasing convection near/at the center... we could have TD#2 reinstated by 2PM if it continues building Convection and expanding it... definitely it will be able to accentuate even more its VORT MAX(s) from 850MB to 500MB further.
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Quoting TampaSpin:
I just completed my take on the Tropics along with StormW if anyone would like to view.


Nice job gentlemen.... You to Spin LOL
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TD2 trying to come back?
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Quoting RitaEvac:
I've noticed Home Depot/Lowes have batteries all over the store, I thought about buying some, but was like.....nahhhhhhh


Because you should have had them by June 1st.
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8 to 10 DAY 500MB MEAN

0z (from today)


12z (from yesterday)
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Good morning Dr Masters,

Thank you so much or the update and the new blog; the other one was really long and full!

I think this blog will be very busy for the next few weeks.

Will be lurking,

Take care,
Gams


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Question for Storm, Canes, Tampaspin, or Orca...

I know models are generally more accurate when we hit the 72 hour window. Statistically speaking once we're within said window, are there any models that are more accurate than the others? I say this because every so often I see a couple of models that predict a path that is WAY off of the others.
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"The small area of convection with ex-TD2 has expanded a bit further to the east, and now covers most of the circulation center"

It's nice to see someone use the correct description of the convection moving east, as apposed to the center moving west. Bravo !
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Looks like we cant go fishing this weekend.
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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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