Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT en Agosto 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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1483. KEEPEROFTHEGATE (Mod)
Quoting Patrap:


there all primers pat for the path of whats yet to come follow that and its where it goes
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1482. Drakoen
Quoting extreme236:


What evidence do you have to prove that?


He is telekinetic with Mother Nature. Only person that would give him a baby...
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90l Still have a broad LLC - will take some time and my feeling is that this will perhaps not reach Hurricane status before 55W! Lot of the models are really bullish on intensity - HWRF is usually on the extreme side - last year it was showing IKE at 170mpg aroud Galveston and Miami on some runs...some of you may remember that....
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1480. IKE
Quoting extreme236:


What evidence do you have to prove that?


He lives in south Florida and that's where the GFS takes it...wishcaster...
Member Since: Junio 9, 2005 Posts: 23 Comments: 37858
Quoting WeatherStudent:


Yup, but the GFS's pattern is more likely to prevail.
It all depends on how strong and where the trough is located then i could tell you which one will prevail, right now remember it's over 3000 miles away from home.
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What evidence do you have to prove that?

and that would put the gulf more at risk
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Poll this.



At. Loop
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Quoting WeatherStudent:


Yup, but the GFS's pattern is more likely to prevail.


What evidence do you have to prove that?
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1474. Drakoen
Quoting tikikopamsxm:
Hi Drak,

Would you mind telling me what do you think will be the strength of 90 L and ex td 2 while passing the northern island

Thanks a lot


I cannot say what the strength of either system will be exactly. Model point towards a strong hurricane bearing down on the Lesser Antilles with 90L. With TD2 models that show development forecast a moderate hurricane in the Bahamas.
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Hi Drak,

Would you mind telling me what do you think will be the strength of 90 L and ex td 2 while passing the northern island

Thanks a lot
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Quoting antonio28:
Thats ones is from yesterday. LOL


Right you are ... my bad, sorry. Removed link.
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Hi Drak,

Would you mind telling me what do you think will be the strength of 90 L and ex td 2 while passing the northern island

Thanks a lot
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Quoting Drakoen:


It is not current
oh my bad i didn't see the "aug13" part, sorry. lol.
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Hi Drak,

Would you mind telling me what do you think will be the strength of 90 L and ex td 2 while passing the northern island

Thanks a lot
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Quoting WatchingThisOne:


lol was just thinking of posting the same thing

A, A, A, A, A, A, etc


Who is sick of polls on how many bloggers are sick of polls? :)

Actually, check out www.intrade.com to see the prediction markets for the hurricane season (you can participate if you are outside the U.S.).
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1464. wally12
Quoting WatchingThisOne:


You sailing out of Calgary? *wink*


Yup... Prairie schooner of course lol
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When models are all this tight then in general they have a good handle and most likely 90L will follow that path! After 55W, they seems to diverge...
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ECMWF takes (ex)TD 2 into South Florida in about 7 days.

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1461. JLPR
Quoting Relix:
90L: I think the northern islands will avoid an impact, maybe the VI. The southern part of the system is it's weakest, we won't probably even receive winds, just rain bands here in PR. It's similar to Luis.... and I remember after putting up everything the system just didn't do a thing, just clouds.

Am I being too relaxed? Probably. Right now I am paying attention to it, but its definitely leaning to 20/80 to impact the islands (FL and NC need to watch out though), especially since all the models have such a good consensus.

By the way, g'evening WU!


I do hope your right =] maybe the fact of being affected by the shear will keep it a little bit more to our south
I guess its too early to tell, at Wednesday we should have a clearer picture
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1460. Patrap
NexSat Viz loop,90L
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Thats ones is from yesterday. LOL
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Got it
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1456. IKE
Quoting CaneWarning:


I am so sick of these polls! Here's a poll:

Who is sick of these polls?

A. I am
B. Give me more polls please!


A
Member Since: Junio 9, 2005 Posts: 23 Comments: 37858
Quoting canesrule1:
yes it is, look at the labeling at the top of the image i posted.


Today is not the 13th.
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1454. Drakoen
Quoting canesrule1:
yes it is, look at the labeling at the top of the image i posted.


It is not current
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Quoting heliluv2trac:
lets take a poll of 90l

A. gulf storm

b. east coast storm

c. fish storm


Gretter Antilles 2009 Major Huricane. Times running out for us here in the NE Caribbean.
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Well I am leaving work. I am going to try really hard to stay away from the blog this weekend. If you see me posting then I failed. I doubt we'll know what this storm will do before Monday anyway. I expect I will be posting later tonight or tomorrow.
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Quoting Drakoen:
That is not the 18z GFDL
yes it is, look at the labeling at the top of the image i posted.
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come on lets make this exciting next week will be a more serious week we might as well enjoy this time some of us may not have electricity to access our computers next week
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1447. Drakoen
That is not the 18z GFDL
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Quoting CaneWarning:


I am so sick of these polls! Here's a poll:

Who is sick of these polls?

A. I am
B. Give me more polls please!
B, lol
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how do I add a picture to my profile, sorry for the dumb ?
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Quoting CaneWarning:


I am so sick of these polls! Here's a poll:

Who is sick of these polls?

A. I am
B. Give me more polls please!


lol was just thinking of posting the same thing

A, A, A, A, A, A, etc
Member Since: Posts: Comments:
1442. Relix
90L: I think the northern islands will avoid an impact, maybe the VI. The southern part of the system is it's weakest, we won't probably even receive winds, just rain bands here in PR. It's similar to Luis.... and I remember after putting up everything the system just didn't do a thing, just clouds.

Am I being too relaxed? Probably. Right now I am paying attention to it, but its definitely leaning to 20/80 to impact the islands (FL and NC need to watch out though), especially since all the models have such a good consensus.

By the way, g'evening WU!
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Quoting WatchingThisOne:
18Z GFDL

Link
Cat 3 before the northern Antilles:
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If anyone cares...the cpu models make (ex?)TD 2 a hurricane.
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Quoting heliluv2trac:
lets take a poll of 90l

A. gulf storm

b. east coast storm

c. fish storm


I am so sick of these polls! Here's a poll:

Who is sick of these polls?

A. I am
B. Give me more polls please!
Member Since: Posts: Comments:
1438. Crawls
Wow, I hope wunderground doesn't blow up - this is the most posts all year!!!!

Can't wait to see what happens when/if this gets closer.
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Quoting heliluv2trac:
lets take a poll of 90l

A. gulf storm

b. east coast storm

c. fish storm


To soon to tell lets wait a few more days and then have the poll

Taco :0)
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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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