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 robie1conobie:
Not to overlook the near future, but the 06z surface analysis has the african wave already at 1006 mb low. Isnt that relatively low for still being over land?


Has a good circulation, and some models are developing it. Wouldn't surprise me to see Claudette out of it.
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We went from one extreme to another.
0-0-0 "Nuttin" to tropical pallooza. This is pretty much expected though. Latter half of August, upward pulse of MJO, less SAL and dry air.
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Where is Dr. Masters? His last update is 25hrs. old.
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5331. fire635
Quoting tarpontexas:
Right behind Ana and TD3 Link


Impressive
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Bill rapidly intensifying!
Member Since: August 31, 2008 Posts: 0 Comments: 833
Quoting P451:
Oh WOW - MODIS caught TD3!



that looks like more than just a TD.
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Not to overlook the near future, but the 06z surface analysis has the african wave already at 1006 mb low. Isnt that relatively low for still being over land?
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5326. jipmg
I think Claudette may be a player soon.. if the Gulf disturbance develops, and we get the african wave to develope, could have have 4 storms in the period of one week?
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5325. Seastep
Quoting serialteg:


just track the storms and dont be caught up in the model hype

thats my trademark phrase right thurr

if this "blog" which is really a message board had a signature feature, i'd have that on my signature - or quote


But it does matter. They won't allow the closing if in the cone...
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Right behind Ana and TD3 Link
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Quoting atmoaggie:


Trying to work out in my head how that forwards speed might affect consolidation attempts and spin up for td-3.
If the windfield stays as broad as it is, no way it gets any stronger than a mid-cat 3.
Anyone?


Well, Dean had a fairly large wind radii. Up to 200 miles wide at around its strongest. Even when it was around 45-50mph, it was around 50 miles wide. It was also moving quicker than TD3 by a smidgen due to that really powerful ridge. Around 18-20mph. Even up to around 25mph at times.

But yeah, I guess on the other hand, Ike had such a massive windfield, towards the end that it couldn't strengthen itself.

Also, as it strengthens, isn't there a chance the windfield contracts?
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AN example of how many posts we get if two storms threaten the US, 5000+ rofl. 27 100 comment pages.
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This is off the subject, you all know the other night when someone put a virus on the blog? I downloaded noscript and since then I don't get the +,- or pictures of any kind. I don't know how to set it up. can someone tell me how? I am sorry for being off subject.

Sheri
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I am now communicating with this blog using the CPU to be used with the live hurricane webcam.

I am mobile for next 4 hours...will get my updates using this system till then.
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5318. rxse7en
Quoting Tazmanian:



yup this is fun is it
You've been on here for years, Taz, and I still have trouble comprehending your posts--especially pre-coffee hours. :D
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Quoting P451:
Oh WOW - MODIS caught TD3!

WOW
Quoting BenBIogger:
0Z 8 to 10 DAY 500MB MEAN



Troughing over the midwest and ridging over the east coast--an ideal setup for east coast hits.
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look for that wave to be come 92L in the comeing days
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5313. Ossqss
Quoting fire635:
210 per hour? We have had over 300 in just the last 1/2 hour. Def lots of activity


Average over the term of the blog and growing :)
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Ana is a distracter and Bill is the real deal.
Member Since: August 31, 2008 Posts: 0 Comments: 833
Quoting Tazmanian:
i say we have TS Bill in the next update

5 pm is my vote. lack of new data until then.
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Quoting Weather456:
The weather channel said the African disturbance shows alot of potential.

WTH? We already have Ana Td 3 and now this?


I guess this is why they didn't lower their numbers too much, lol. This is going to be insane if the pattern doesn't break.
Quoting BiloxiGirl:
I think I see a tiny spin over the keys.


Link

Its a pretty good spin a few K feet up...
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5308. fire635
210 per hour? We have had over 300 in just the last 1/2 hour. Def lots of activity
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Quoting robie1conobie:
s. fla is not the hurricane capital of the world. Someone posted earlier how rare it is for a storm not to hook it one way or the other away from s. fla.


I still believe it holds the highest probability of getting hit.
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Quoting Weather456:
The weather channel said the African disturbance shows alot of potential.

WTH? We already have Ana Td 3 and now this?



yup this is fun is it
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Quoting PELSPROG:
Thanks Dr. Masters.

for what. his update for today has not come out yet.
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ANA

TD3
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Quoting SoFla:
5249. serialteg:
Too bad the closing on our house is in So. FL instead of Utah - smack dab in the middle of all the predictions for these storms!


just track the storms and dont be caught up in the model hype

thats my trademark phrase right thurr

if this "blog" which is really a message board had a signature feature, i'd have that on my signature - or quote
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Quoting IpswichWeatherCenter:


Um - That is just uber-off topic.

Anyway.. which do you prefer:

A) Ana gets into Gomex before disappating
B) Ana merges with TD 3
C) Ana becomes a fish
You pu tup another Poll and have the nerve to call my post off topic
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I agree that my prior comment of South Florida being the safest place was wrong. I was just making case that any slight deviation can be a good thing for South Florida. The rest of Florida, GOM, and east coast could be another story. Looking more and more like a "potential" problem in the GOM down the road. It is just too early to tell. The east coast should be keeping their guard up as well because any sudden weakening of the ridge will allow for recurvature.
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5299. fire635
Quoting Tazmanian:
i say we have TS Bill in the next update


I agree... its certainly looking organized enough to be named soon. I actually expected it at 1100
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5298. jipmg
Alright, forecast is the system "td 3" is expected to continue to move W to WSW in the next 6 hours or so, then move w, and once it gather strength move WNW, the ridge might weaken as it nears the bahamas moving it NW then strenghtening pushing "Bill" towards the W to WNW
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wow, rapid intensifying for 03L
Quoting Tazmanian:
i say we have TS Bill in the next update

Agree
Member Since: August 31, 2008 Posts: 0 Comments: 833
The weather channel said the African disturbance shows alot of potential.

WTH? We already have Ana Td 3 and now this?
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5293. Ossqss
210 post per hour has got to be a record. Good stuff all, thanks
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5292. CJ5
Quoting ALCoastGambler:
I do hope with Dr. masters new update that admin. steps in. There is no reason for +5000 posts in a busy time like this. Too hard to keep up. +5000 posts and +2000 Is it coming to SFL


Hmm...you don't really have to "keep up" with the previous posts...I don't see any big deal. He will get a new one when he gets one.
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Why yes, old chap! :-)
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5288. Seastep
Intensity charts:

Ana

TD3
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i say we have TS Bill in the next update
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Quoting P451:
TD3




ANA


What time were those (really would prefer to see it on the plot given the behavior of some others in here.)
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I think I see a tiny spin over the keys.
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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.