TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 02:38 PM GMT on Αύγουστος 13, 2009

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Tropical Depression Two is near death, but is still worth watching. The dry, Saharan air to the north and west of the depression, combined with moderately high levels of wind shear of 15 - 20 knots, have almost completely destroyed all of TD 2's heavy thunderstorms. Satellite loops of the storm show a well-formed circulation, but almost no heavy thunderstorm activity.

Wind shear over TD 2 is expected to remain in the modereate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C three days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to to TD 2's north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that TD 2 will not be able to intensify quickly, and some of the models indicate the TD 2 may get destroyed in the next day or two. However, several models still predict TD 2 will become a tropical storm. The HWRF model predicts TD 2 will become a hurricane five days from now, but this seems unlikely given the dry air and relatively high wind shear affecting the storm.


Figure 1. Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

African tropical wave 90L
A strong tropical wave with a large circulation and plenty of heavy thunderstorm activity is a few hundred miles south of the Cape Verdes Islands, off the coast of Africa. NHC dubbed this disturbance 90L this morning. This morning's QuikSCAT pass shows that 90L has a very large circulation, and top winds of about 30 mph. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are in two major bands, to the north and to the south of the center. There is no heavy thunderstorm activity near the center yet, and this would have to happen before 90L can be named Tropical Depression Three. 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 has been. Wind shear is about 20 knots over 90L, and is forecast to remain in the moderate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days, which are high enough above the 26°C threshold for tropical cyclone formation to allow some slow development to occur. The GFS and ECMWF models continue to predict the development of this wave, though they are now less aggressive about intensifying it than they were in earlier runs. The consensus among the reliable HWRF, GFDL, GFS, and ECMWF models is to bring 90L to point near or just north of the northernmost Lesser Antilles Islands 6 - 8 days from now. The storm could be at hurricane strength by then, as forecast by the SHIPS intensity model.

I'll have an update Friday morning.

Jeff Masters

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Quoting Weather456:
Every met office in the Leewards are talking about 90L


With good reason.
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This run is not looking good for Long Island, NY.. It catches the trough but high pressure looks to build in and keep it from moving east.

12Z GFS 276 .. A stronger storm then the 06Z run.
Must remember that the 12Z and 00Z runs are more accurate then the 06Z and 18Z runs.

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It's surprising to me how much SE shear 02 is experiencing. Its forward motion should counter some of that, but those thunderstorms are just racing off as they blow up.
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Good afternoon! Just wanted to drop some quick thoughts from some quick analysis this morning.

In regards to Tropical Depression 2, don't write the system off just yet. In watching the latest Tropical RAMSDIS visible loop, the depression still maintains a very well defined surface circulation and an impressive low-level structure. With this, you can never rule any system out. But, its going to have to put up an amazing fight in order to survive as the latest CIMSS SAL analysis product shows dry, stable air in the immediate path of the system for a few hundred miles. This has been the main reason for the problematic convective development with Tropical Depression 2. According to the latest computer models, wind shear may gradually improve to marginally favorable conditions after 48 hours and moisture should also increase after 48 hours as well. In my forecasting opinion, Tropical Depression 2 still can't be written off despite the inhibiting factors affecting the system currently. Going down the road, I really like the NHC forecast track except I expect this to become a tropical storm at some point in the next 72 hours.

Now, getting onto the talk of the Wunderground town: Invest 90L. Even though I try to maintain a rational approach, I must admit that this system looks very impressive due to the sheer immense coverage and expansive circulation. But, this size will mean that this system will take some time to get organized into a tropical cyclone; about 48 hours. The satellite presentation is very intriguing with spiral banding arms centered around the circulation center. It has the pinwheel appearance like most developing tropical cyclones do in the Pacific which makes this system quite unusual for the Atlantic and makes me think this COULD become a big playa down the road. In analyzing the computer models, I don't see any unfavorable factors for this system to develop in the future except for the sheer massive size in the present. Now, I must reiterate that there is NO need for concern or excitement at this time since this remains so far out there and as we all to well know, things can change quickly in the tropics. For now, we just need to monitor the situation.

One last feature that has caught my attention just due to my local interest is the tropical wave crossing the Northern Caribbean over the Dominican Republic. Convection has been increasing due to interaction with a gradually weakening TUTT. As this progresses westward towards the Florida Straits and Cuba, there's a slight chance that something could attempt to spin up, but no computer model really shows this. But, it still bares watching since its close to land and will be entering very warm waters and somewhat favorable upper level conditions.
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Every met office in the Leewards are talking about 90L
Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
430. 7544
ok dont laugh but it covers the whole eastern seaboard this run from fla to and up so longgated lol

Link
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can someone give me a link to the latest models, thanks.
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12Z GFS Shifted back to the left as expected... is having a little hard time timing the trough that will pull it WNW to NW and the strength of the building High after the trough departure.
Member Since: Αύγουστος 14, 2008 Posts: 4 Comments: 4972
Quoting Funkadelic:


I dont know why you wrote "Still not looking good"

If I were you I'd be like OH @#$% it looks alot wors for the isdland on this run, due to the fact that it shows a stronger system.

I Wish you the best luck down there next week, Just listen to some bob marley and relax while you still can :)



still not look good for the islands
Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
Quoting jasoniscoolman10:
very exposed center with a little patch of convection, i think its over with 02L, just my personal opinion.
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Quoting 7544:
407. Acemmett90
you got to to go with your gut its all good

or you can go with what the NHC says and the local weather service.

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Quoting IKE:
12Z GFS at 162 hours...




6Z GFS at 168 hours...



IKE - now that's scary.
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The blob of convection near the center of TD 2 heeps growing.
Member Since: Δεκέμβριος 21, 2007 Posts: 13 Comments: 3046
Quoting Drakoen:


I have a hard time believing anything can hit the U.S. with that kind of trough in place

Drak, just to clarify for us lurkers, you're saying recurve north of the islands? (Assuming the trough is in place). TIA
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Quoting Acemmett90:

ok you can pick on someone else now
now i realize why someone planted a virus on this site


I wasn't picking on you. You said you very worried. I was attempting to calm you.
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the 6z run is the only one that slowed it down like that. clearly that run was slowing the forward motion.

all the other plus the latest 12z run looks about the same.
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413. 7544
407. Acemmett90
you got to to go with your gut its all good
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Quoting IKE:


It shows it 800 miles further west on the 12Z run compared to the 6Z at the same period in time. Something ain't right.


I mentioned it this morning, 06Z GFS split 90L in two which resulted in a eastern most low and resulted in later solution by the GFS. I also said it should change sine the 12Z and 00Z runs are more reliable.
Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
Can somebody give me a link to the latest model runs, thanks a lot!
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409. IKE
Quoting Acemmett90:

ok you can pick on someone else now
now i realize why someone planted a virus on this site


That talk is uncalled for and could get you banned on here.
Member Since: Ιούνιος 9, 2005 Posts: 23 Comments: 37858
Quoting SomeRandomTexan:
I may be eatig crow later but I don't think the area of interest in the Bahamas will amount to much... If anything were to happen it would take quite a bit of time.. the is currently no vorticity in the area and the ULL interacting with it should keep in in check.. jmho
None of us should feel like an idea of ours that didn't pan out is eating crow. There are many possibilities, and the weather, especially tropical, is very uncertain, as we've all seen numerous times.
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Quoting 7544:


agree the low is now tring to intestify as per our local mets stay tuned
yeah, and the pressure,= is down, near 1007 millibars
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Similar to Td 2



but models think otherwise

Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
Quoting Drakoen:


I have a hard time believing anything can hit the U.S. with that kind of trough in place


That's for sure... unfortunately it comes down to timing.
Member Since: Αύγουστος 14, 2008 Posts: 4 Comments: 4972
Please check out my blog, thanks!
Link
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Quoting Acemmett90:

maybe it because i have a bad feeling about this storm i am usually not like this

well it isn't even a storm yet technically, is it? I tend to save my bad feelings until something is at least within a three day chance of me. Realistically, this is WAY out there. You can remain calm.. lol
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Any guesses as to when 90l will become Ana? My guess is sometime after Friday as it is a large system and needs some time to organize. I do believe once it reaches depression status it will ramp up to a hurricane fairly quickly (possibly as early as Monday). I won't take much stock in the model's long term tracks until it gets a closed COC. Any thoughts.
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398. 7544
Quoting canesrule1:
i think red is very likely.


agree the low is now tring to intestify as per our local mets stay tuned
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Quoting chevycanes:

too bad there is no way for them to know that with even 90% certainty.

Quoting Patrap:
Due to 90L's size its going to take some time for TD status,as angular momentum and conservation of energy will take her awile to get going.

A Storms size is usually determined at Genesis..Small remain small to a extent,and Large do the same.
A cat 3 Large storm can do much more damage and overall Impact than a Cat 4-5 Smaller storm as a rule too.
That is what I have always thought as well. Case in point, '44 hurricane, which hit Jersey Shore and Northeast my area, of which I always talk about, not meaning to repeat myself ever if I do! '44 was an enormous 2 or 3, pretty well out to sea, but it gave us 100 mph winds and a legendary storm surge that destroyed Atlantic City's boardwalk and many others. It's that scenario I fear the worst. Our shore's angle makes it unlikely for a direct hit, although it has happened, and could again (1903, 1821). More likely though, it would be a big storm, off to our east, that throws us wind and surge on its "weak" side: '38, '44, Carol, Donna...all similar.
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A question about the SAL - Dr. Masters said a while ago that this should be a quieter year for dust action. But here we are, seeing it interact with and help to destroy a number of potential storms, wrapping around TD2 in this a.m.'s NHC report. Anyone with an analysis of SAL action for the remainder of the season, or maybe suggest a link where I could find it?
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Quoting WxLogic:


That's the key... if that first shortwave is strong enough it will cause to go through the Islands, else if its not deep enough then it should shave the southern Greater Antilles...


I have a hard time believing anything can hit the U.S. with that kind of trough in place
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394. IKE
Quoting Weather456:



still not looking good


It shows it 800 miles further west on the 12Z run compared to the 6Z at the same period in time. Something ain't right.
Member Since: Ιούνιος 9, 2005 Posts: 23 Comments: 37858
Quoting CaneWarning:


I think they might in the next TWO.
i think red is very likely.
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391. 900MB
P.S.- Is it safe to click on links yet? Did they fix the virus problem? Thanks, 900MB
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Quoting IKE:
12Z GFS at 162 hours...




6Z GFS at 168 hours...




still not looking good
Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
Just posted my brand new blog! Please check it out!
Link

Thanks!
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Getting its act togther..

http://www.nrlmry.navy.mil/nexsat
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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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