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 Weather456:
5 days HWRF - they differ in track but agree that 90L will be something to watch



WTF?? I see 948 mb and that's not even close to the center! That's freakin crazy.
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1882. IKE
That GFDL 18Z is showing the COC at near 16N and 63W in 5 days...that's 150-200 miles southeast of PR.
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Quoting IKE:


I have a feeling the cloud tops are going to explode...maybe not tonight, but sometime this weekend.



Was katrina not also 'expected' for SF originally, then skipped a bit South into the Gulf?
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Quoting Weather456:
5 days HWRF - they differ in track but agree that 90L will be something to watch



Cat 5?
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Former TD2 looks very good right now, the TWO will be interesting, wouldn't surprise me they change it to code red.
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Watching the models right now is as useful as watching a girl pick out clothes. They cant make up their minds and wont be abll an actual storm forms. I said before huricane season even started how quiet it woud be with less activity than 2006 and so far i am right. Im rarely wrong when it comes to hurricanes. Im telling you guys this is all much ado about nothing. they may become storms but 90l is never gonna reach severe hurricane status and will likely turn out to sea. And 1 thing i can guarantee is that the US is completely safe from both of these systems.
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Quoting IKE:


Heck...that's west of you!


That would make me think its going into the gulf.
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5 days HWRF - they differ in track but agree that 90L will be something to watch

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1874. IKE
Quoting Tracker09:
90 l is getting better organized!!1 this is gonna be a big one, i haave a bad feeling in my stomach!!!!! ewww i feel bad for s fl! since all of the ensemble models take it there, well most of them


I have a feeling the cloud tops are going to explode...maybe not tonight, but sometime this weekend.

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Quoting Vortex95:


I must say you haven't given out too many compliments to systems.


I call them as I see 'em. I thought TD2 would be toast by now, but I am quite surprised by its comeback.
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Quoting Weather456:
5 Days



What the ...is THAT?

Ouch.
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Quoting Weather456:
5 Days - GFDL



Where'd you see that? That looks strong.
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90 l is getting better organized!!1 this is gonna be a big one, i haave a bad feeling in my stomach!!!!! ewww i feel bad for s fl! since all of the ensemble models take it there, well most of them
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1868. IKE
Quoting Weather456:
5 Days



Heck...that's west of you!
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Quoting extreme236:


I'm not trying to be rude but everytime someone tells you something to show its not going to S Florida you tell them no and that its doubtful.


His achy brachy heart for a storm has noooo idea what kind of sh!# he is asking for especially down here in SoFlo. It gets pretty nasty for a non event let alone an actual Cat.
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1865. IKE
Quoting DestinJeff:


JFVWSter has done something few have accomplished, if any. He has carved out a niche on the blog as an overt WC, without getting too much flaming for it. The ironic truth is probably that he is representative of far more bloggers than we'll ever know, and perhaps is represenative of us all to some degree or another. His input adds to the discussion, and has been accepted here as a regular.


Whatever makes him happy.
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5 Days - GFDL

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Quoting WeatherStudent:


No offense taken, my friend.


You are my favorite blogger!
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1860. Patrap
GFS 18Z run
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Quoting Grothar:
I do not believe she is speculating. She has been instrumental in systems development for model projections and works actively in the field. This was information she just passed on to me from her current work. Neither I, nor she were speculating. I just thought the information might be of interest. I do not know enough about the dynamics of weather as I have always mentioned in my blogs. I sincerely apologize if the inference was one of confirmed information. I just enjoy this blog and find all the comments interesting.


Apology accepted. Sorry for my passive-aggressive post. Now please enjoy this EUMETSAT picture:

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gfl has it going up the east coast now
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1856. amd
according to the latest shear maps in the Atlantic ocean, there is 20 to 30 knots of easterly shear in the region from 10N 30 W to 13 N 40 W.

Also, there is some substantial westerly shear in the vicinity of the northern leeward islands.

Link

Now, i don't want to sound like a downcaster, whatever that means, but how can either 02L or 90L develop in any real significant matter with the shear pattern as is?

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how strong is the trouf suppose to be next week
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I have to admit i would love to be in a hurricane for the thrill but i dont want one because of the horror and lives they ruin...Put me out in a boat in the midlde of the Ocean and i'd be happy haha
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Quoting JLPR:
Interesting...
Ada Monsn here said that 02L should clear the dry air for 90L

02L should pass to the north of PR
and 90L is a bigger threat since it could pass according to her anywhere from 50 - 100 miles to our north or south or end up affecting us directly, she sounded a little worried =\

Yes, is the first time in many years that I see the people in the island including the news media so worry about a system that is not yet classified as a tropical depression. I'm pretty sure is because the models target seems to be "Puerto Rico".
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I must say that ex/future-TD2 is insulating itself from the dry air quite well. 90L is still very much embedded in the ITCZ.
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GFDL only goes out 126 Hrs. so its not showing anything in the gulf yet.
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1848. Grothar
I do not believe she is speculating. She has been instrumental in systems development for model projections and works actively in the field. This was information she just passed on to me from her current work. Neither I, nor she were speculating. I just thought the information might be of interest. I do not know enough about the dynamics of weather as I have always mentioned in my blogs. I sincerely apologize if the inference was one of confirmed information. I just enjoy this blog and find all the comments interesting.
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This thing must be watched extreme, because it has rotation and its hot.
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1846. Patrap
I do plan to see IG when it comes out and District 9 this weekend
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1845. mkmand
It looks to me that both of these sytems should be TDs. When is the next advisory?

BTW, 1st post since last year :)
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Quoting WeatherStudent:


Highly doubtful, acere. Link, plz?


I'm not trying to be rude but everytime someone tells you something to show its not going to S Florida you tell them no and that its doubtful.
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I'm gonna keep an eye on that surface trough across the Florida, NE Gulf, and southeast US area...could be of some concern eventually.
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1840. IKE
Quoting Patrap:
For my Bud Ike,and Hopefully we wont be breaking this one out in a weeks time..


A+ R & R.
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Quoting Vortex95:
I forgive you Pat for the most part but I sentence you to go see Inglorious Bastards to prove your non facist ways!!!

anyways 02L is getting better but it isn't a TD yet and likely won't be tommorow. Just wait it out and TD2 will come.


Well I'm not willing to say 02L wont be a TD tomorrow. It may be small, but its the best its looked all day. Probably a T1.5 right now, maybe a tad higher.
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This thing approaching the gulf could get serious quick. sst's, Low shear, slow movement. Not good,not good...comments?
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The GFDL has it going straighth in the GULF JFV so it could go south of you and not even affect you...dont get over excited
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The latest GFS shows a 2nd system crossing the leewards @174H... only a few days after 90L! I'm impressed andI can't imagine how bad it could be for the islands.
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Quoting Ldog74:


I was referring more to individuals' comments on the possibility of rapid intensification than what the models are showing. But it seems to me that the SHIPS is being a little bullish, topping out just below Cat 3 strength in 5 days. Thats based on 90L being a mid range TS by this time tomorrow, which I am just not seeing.


They certainly are being bullish, and I do believe development in its TS stage will be gradual, but once it becomes a hurricane not much stopping it at that point. So, at this time I believe the SHIPS, GFDL, and HWRF forecasts are valid in terms of intensity.
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.