TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 2:38 PM GMT on August 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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1787. Drakoen
GFS is way too inconsistent with the speed of this system to be considered credible.
Member Since: October 28, 2006 Posts: 57 Comments: 29919
I could not help but notice today the huge flare up of storms around the wave by Cuba/Caribbean. I know locally they're forecasting any rain, but is there a chance of this being a Depression/Storm with its recent flare up?
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Seems like all the 18z GFS runs have it into the Gulf the past few days.
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1783. Dakster
Wassup WeatherStudent.

What's your take on the ex-TD2? Is it completely dead or up for revivial?

Member Since: March 10, 2006 Posts: 0 Comments: 10034
Quoting WxLogic:


All I can say based on trends that I've noticed is that the Leeward Islands and Greater Antilles need to watch this one closely. I personally believe there could be a 60% change of a possible path through the Islands... in my opinion. So definitely it will be good to revise your shelter plan/needs and just be ready and if it doesn't go through then at least you were safe than sorry.


both comments are very insightful..i wanna know to be ready here in puerto rico...

Member Since: July 14, 2008 Posts: 0 Comments: 246
1780. KEEPEROFTHEGATE (Mod)
Quoting tbrett:


Some of us in the Antilles would like to have an idea of where it is going before it gets here.


what i have right now
stay tuned in coming days thats the best advice

394

WHXX04 KWBC 131720

CHGQLM

ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL DEPRESSION INVEST 90L



INITIAL TIME 12Z AUG 13



DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT

REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD

NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC

OFFICIAL FORECAST.





FORECAST STORM POSITION



HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)



0 11.9 22.2 280./ 7.0

6 11.9 24.3 272./20.4

12 12.4 25.4 292./12.0

18 12.5 27.4 273./19.4

24 11.9 28.9 249./15.3

30 11.4 29.6 236./ 8.7

36 11.4 30.2 264./ 5.5

42 11.6 30.8 288./ 6.5

48 11.7 32.2 273./14.3

54 11.9 33.4 280./11.3

60 12.2 34.9 283./15.1

66 12.4 36.8 275./18.3

72 12.6 38.5 278./16.9

78 13.0 40.1 284./15.9

84 13.6 41.8 289./17.8

90 14.2 43.7 287./19.3

96 14.7 45.6 285./19.3

102 15.2 47.6 283./19.8

108 15.4 49.5 277./18.0

114 15.8 51.3 281./17.9

120 16.2 53.3 284./19.6

126 16.6 55.2 281./19.0
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting CaneHunter031472:
Have you guys/gals seen the wave comming after 90L which is still over Africa? I see rotation on that one as well.
Yes we got a train of waves now!
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1777. WxLogic
Hehe... well on this run is back to IKE's house.
Member Since: August 14, 2008 Posts: 4 Comments: 4933
1776. Drakoen
SFL then GOM hit LMFAO!
Member Since: October 28, 2006 Posts: 57 Comments: 29919
Drakoen do u have the link for the 18z gfs...TIA
Member Since: August 7, 2009 Posts: 0 Comments: 251
This GFS run is faster than the previous

uh oh
Member Since: August 29, 2006 Posts: 22 Comments: 1342
5 knots of shear over the MLC/LLC. Just updated.

Member Since: June 9, 2007 Posts: 4 Comments: 15790
Quoting DM21Altestic:
I have a question. Why didn't Ike recurve like it was supposed to? I thought the rule of thumb in the atlantic is if a storm hits 20N before 55W, especially as a hurricane, it ALWAYS recurves.

Ike should have recurved in the mid atlantic as a Cat 4 hurricane, since it was north of that latitude. Why did it keep going westward?


There is no rule of thumb when it comes to hurricanes.
1770. WxLogic
Quoting Drakoen:
This GFS run is faster than the previous


Yeap... moving ahead before the trough starts digging in.
Member Since: August 14, 2008 Posts: 4 Comments: 4933
1769. Drakoen
This GFS run is faster than the previous
Member Since: October 28, 2006 Posts: 57 Comments: 29919
Have you guys/gals seen the wave comming after 90L which is still over Africa? I see rotation on that one as well.
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Quoting Weather456:
Infrared/Shear/Surface obs


it look like ex-td2 is entering lower wind shear so redevelopment is possible if it can get convection around the COC
Member Since: June 13, 2009 Posts: 2 Comments: 11166
La boy, when you in anyway on this blog say that a storm may die or turn to sea or express anything positive be prepared to be ripped part. They will call you a downcaster,a stupid amateur or a troll, but in reality they seem to want hits on USA. Some think this is their blog.Some put you on their ignore list (self-censorship). Sad but true.

That is true to a degree i have been on here long enough to know that but in the end a good meteorologist(even though i'm not one yet) calls it like they see it not to start anything but i could care less what they say i try to be as accurate as possible
Member Since: August 29, 2006 Posts: 22 Comments: 1342
1764. WxLogic
Quoting tbrett:


Some of us in the Antilles would like to have an idea of where it is going before it gets here.


All I can say based on trends that I've noticed is that the Leeward Islands and Greater Antilles need to watch this one closely. I personally believe there could be a 60% change of a possible path through the Islands... in my opinion. So definitely it will be good to revise your shelter plan/needs and just be ready and if it doesn't go through then at least you were safe than sorry.
Member Since: August 14, 2008 Posts: 4 Comments: 4933
Quoting Relix:
TD2 is fighting the good fight! I wouldn't mind a minimal TS here in PR to be honest =P. 40MPHs. Quick passing. Bring a thrill or two. Anything beyond TS is not welcome here in PR though! shoo shoo sho!


estoy de acuerdo....i agree with you.. even with an Invest we have a lot of troubles here in pr..remeber last year...
Member Since: July 14, 2008 Posts: 0 Comments: 246
1758. amd
Quoting DM21Altestic:
I have a question. Why didn't Ike recurve like it was supposed to? I thought the rule of thumb in the atlantic is if a storm hits 20N before 55W, especially as a hurricane, it ALWAYS recurves.

Ike should have recurved in the mid atlantic as a Cat 4 hurricane, since it was north of that latitude. Why did it keep going westward?


very strong high pressure in the central Atlantic blocked Ike's movement to the north, so that continued it to the west.

The track toward Texas was locked in stone after a high pressure in the gulf bridged with the the large high pressure in the central Atlantic.

But, I think the bridging occurred due to a strong trough in the Pacific which forced the high pressure in the gulf to move toward the central Atlantic high, causing the bridge. IMHO.
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What about TD2?

Way to much Easterly shear the environment could become more favorable when it gets closer to the bahamas if it can hold together
Member Since: August 29, 2006 Posts: 22 Comments: 1342
Hey Savannah - things are GREAT here. Perfect weather, marine layer keeps it cool in the morning and then warms up in the day, cool again at night.

I heard about all the rain back there - my neighbors shot a photo of the flooding in our neighborhood (we still own the house there for now)...flood was about a foot up our mailbox. I DO miss the thunderstoms though...reluctantly parted with my weather radio and gave it to my neighbor when I left.

Thank God that the rain held off until they brought Captain Freeman home...I heard after he was brought to the funeral home, the skies just opened up.

Story of the soldier (link...if you want to cut and paste it...not putting any links up since there has been so much of a problem).
http://www.bryancountynews.net/news/article/4455/
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1754. tbrett
Quoting SavannahStorm:Give the system about 4-5 days, then we'll have a much better idea of where it is going once it reached the Antilles.


Some of us in the Antilles would like to have an idea of where it is going before it gets here.
Member Since: July 20, 2007 Posts: 0 Comments: 107
What about the ones that don't?

Well your free to choose which models you lean on more
Member Since: August 29, 2006 Posts: 22 Comments: 1342
1751. Relix
Quoting Prgal:

I dont mind a tropical storm, but I dont want another David, Hugo or Georges. No way!

No! Though to be honest we are quite overdue from receiving the full brunt of a Cat 5. It's been what... nearly 70 years? Statistically we are about to be hit by one soon. I am honestly ready for that one with the sole exception I live 1 mile away from the beach =P
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It appears that, of all things, a La Nina is developing in the Atlantic:

Member Since: May 21, 2006 Posts: 5091 Comments: 114758
Quoting DM21Altestic:

no, silly, it seems like whenever there's two weak storms in the vicinity of one another the "Fujiwhara" word gets mentioned, which is quite insane because in actuality it's a rare occurance and only happens between two mature hurricanes or very strong tropical storms.

Its not as rare as you might think and in theory could affect any two cyclones or anticyclones and is far more likely to be a regular occurence that just goes mostly unnoticed except in extreme cases.
Member Since: August 27, 2008 Posts: 0 Comments: 1497
Some convection building on 90L.
Member Since: July 8, 2005 Posts: 259 Comments: 23606
that i agree lol

Oh so i redeemed myself? lol
Member Since: August 29, 2006 Posts: 22 Comments: 1342
1741. rxse7en
Quoting DM21Altestic:

no, silly, it seems like whenever there's two weak storms in the vicinity of one another the "Fujiwhara" word gets mentioned, which is quite insane because in actuality it's a rare occurance and only happens between two mature hurricanes or very strong tropical storms.
I don't think it requires mature systems, just cyclonic vortices. More mature systems probably see a larger effect, hence my "slight" comment.
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Infrared/Shear/Surface obs

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1738. TxKeef
Quoting rxse7en:
Are TD2 and 90L developed enough for a slight Fujiwhara effect? Perhaps TD2 will start a more southerly track if it's not absorbed?


I'm not positive but I'm pretty sure they'd both have to get quite a bit stronger before that could even become a possibility and even then I'm not sure they're close enough to eachother. but don't quote me on that:P
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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.