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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About to head out of here for the evening, hope everyone has a nice night!

Final thoughts:

TD2 bears watching as indicated by the NHC. As long as some convection continues to fire - that is mass that is being pulled from the center of the low and should act to keep the central pressure lower than the environment around it. This in turn will help sustain the nice low level circulation and keep it poised to possibly strengthen somewhat if shear conditions improve.


90L looked better this afternoon and has regressed a bit in organization. However, as NRT posted, the pressure was falling pretty sharply this afternoon. This should help pull the circulation together over the next 24 hours and get us closer to a depression or storm. Also, the easterly shear over 90L is forecast to relax slowly to more favorable conditions tomorrow.

Finally, the SSTs will warm a bit tomorrow which will make the environment more unstable and support additional convection.

Member Since: Posts: Comments:
1534. Skyepony (Mod)
I've got the nowCOAST up on the big monitor all blown up on the wave N of Hispanolia, got the wind barbs on. It's set to refresh every 4 mins. A weak west wind has just appeared on the south end of Haiti.
Member Since: August 10, 2005 Posts: 210 Comments: 39137
Quoting java162:


is there a way to get the forcast tracks for dean when it was at the stage like invest 90?


I dont think so.
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1532. Drakoen
The graphics from StormVista contradict the graphics from Earl Barker
Member Since: October 28, 2006 Posts: 57 Comments: 30727
WS FYI horses and cows don't drink from throughs. ;)

I wouldn't have said anything but it is his favorite word and he is pretending to spell correctly again.
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Quoting DM21Altestic:
POLL: What kind of storm will 90L resemble most, as far as track and intensity?


A) Hurricane Bertha (2008)
B) Hurricane Georges (1998)
C) Hurricane Isabel (2003)
D) Hurricane Ivan (2004)
E) Hurricane Andrew (1992)
F) Hurricane Floyd (1999)
G) Hurricane Helene (2006)
H) Hurricane Allen (1978)
Z) 90L won't become a hurricane at all.

...Bold your choice...


Y. None of them, Irene 2005
Member Since: Posts: Comments:
Quoting P451:
Africa...the gift that keeps on giving.



train of storms....Which ones will affect land and where???
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Quoting BenBIogger:
Enough with the polls!



am with you stop with the polling Please


if you want to do that take it too your own blog not here
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Quoting P451:
Africa...the gift that keeps on giving.



Hey P451 can you please give me a link to where you got that?
Member Since: Posts: Comments:
1526. KEEPEROFTHEGATE (Mod)
we have to stop with the polls to many its becoming annoying i will request admins assistance if needed please stop with so many of them
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Amazing, 2 days ago we had 2 named storms and an invest by the bloggers. Now all we have is 5 polls...Wow what a couple of days make.
1524. java162
Quoting Stormchaser2007:


Dean.


is there a way to get the forcast tracks for dean when it was at the stage like invest 90?
Member Since: Posts: Comments:
It seems some people are seeing such a large area of clouds and thinking 'wow, 90L is impressive/a beast/etc'...really it's the opposite. That thing is sooooooooo stretched out now. The quicksat map shows it well, a definite circulation, but in the shape of a hot dog bun, not a bagel.
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Rem low near the Bahamas.

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1521. IKE
18Z NAM.....has EX-TD2 entering the eastern Caribbean on the end of it's run.
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Quoting hurricanehanna:
when did this become a poll blog??? lol



LOL
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Quoting TampaSpin:


Thanks for the advice....it was all in fun since 99% was calling 90L Bill.....but your correct.



your welcome i this dont want you be see you get ban
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1515. ssmate
Quoting hurricanehanna:
I still say we need to keep a close eye on the Caribbean wave as it approaches the GOM - lots of moisture, low sheer and hot water to work with....

I agree completely. This dynamic is very interesting.
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1513. java162
Quoting canesrule1:
E


B
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Quoting cg2916:

it was from 3:12 PM EST.
Now that you mention it, it is. It does still need to tighten the circulation and build and organize convection.
yeah, on visible it looks like a weak TS but on AVN it looks like a cloudy day, and 90L needs to tighten up its COC and needs the Dvorak classification to bump it up to a T1.5 or T2.0 then we will have 03L
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This freaking sucks! Could something just develop already. We need some excitement and before anyone flames me...yes I know what it is like to live in a FEMA trailer. I still love the excitement a well formed cane brings.
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when did this become a poll blog???
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Enough with the polls!
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Quoting Drakoen:
Let's hope this does not happen as the CFS forecast for the second half of September thru 1st of October. This be negative NAO.



why??? will we or will we not see any name storms???
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Quoting DM21Altestic:
POLL: What kind of storm will 90L resemble most, as far as track and intensity?


A) Hurricane Bertha (2008)
B) Hurricane Georges (1998)
C) Hurricane Isabel (2003)
D) Hurricane Ivan (2004)
E) Hurricane Andrew (1992)
F) Hurricane Floyd (1999)
G) Hurricane Helene (2006)
H) Hurricane Allen (1978)
Z) 90L won't become a hurricane at all.

...Bold your choice...



Dean.
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Quoting Tazmanian:
guys can we may be watch what we post in here the Admins will be baning we are in a active periods of hurricane season right now with 90L



so TampaSpin may want to re move that photo or he may end up being ban for 24hr that photo is not posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself.


am sure its find if we dont have any thing too talk about but its not find right now


Thanks for the advice....it was all in fun since 99% was calling 90L Bill.....but your correct.
Member Since: Posts: Comments:
Quoting DM21Altestic:
POLL: What kind of storm will 90L resemble most, as far as track and intensity?


A) Hurricane Bertha (2008)
B) Hurricane Georges (1998)
C) Hurricane Isabel (2003)
D) Hurricane Ivan (2004)
E) Hurricane Andrew (1992)
F) Hurricane Floyd (1999)
G) Hurricane Helene (2006)
H) Hurricane Allen (1978)
Z) 90L won't become a hurricane at all.

...Bold your choice...



Floyd, because of its shear size.

But Dean is a much more similar comparison.
Member Since: Posts: Comments:
1502. Drakoen
Quoting TexasHurricane:


Why? What does it mean?


Less troughs. More ridge. Heighten east coast risk.
Member Since: October 28, 2006 Posts: 57 Comments: 30727
Quoting DM21Altestic:
POLL: What kind of storm will 90L resemble most, as far as track and intensity?


A) Hurricane Bertha (2008)
B) Hurricane Georges (1998)
C) Hurricane Isabel (2003)
D) Hurricane Ivan (2004)
E) Hurricane Andrew (1992)
F) Hurricane Floyd (1999)
G) Hurricane Helene (2006)
H) Hurricane Allen (1978)
Z) 90L won't become a hurricane at all.

...Bold your choice...

E
Member Since: Posts: Comments:
90L looks to be organizing pretty well. I'd say Saturday on it being TD 3, seeing as it is a large system and will need time to fully organize and get proper convection at the center. As for ex-TD 2, I'd still monitor it, it still has a strong circulation with some pulsing convection, and could regenerate later. Some have said 50-55W, I'd have to agree that would be a good opportunity for it to happen if it does.
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Quoting Ameister12:
Poll Time!!!

Do you think ex-TD2 is going become a depression again?

A) Yes
B) No
C) Maybe


A)YES
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1498. IKE
Quoting java162:


well then this blog is not for you.


After 21,000+ posts, I'll hang around.
Member Since: Posts: Comments:
1497. KEEPEROFTHEGATE (Mod)
Quoting jaevortex:


Hey.. I've been here for a few years lurking.. and reading WS comments I've been wondering could he be dyslexic?

This season is off to a slow start, but by next week this blog will be going nuts with all the storms forming. 90L scares me but I'm still weary of TD2 as well as the wave near Cuba. I reckon it's a race to see which of these storms/waves will be "Ana"

-goes back to lurking-


its the tropics ...and its august anything can happen anywhere anytime anyplace
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Quoting Drakoen:
Let's hope this does not happen as the CFS forecast for the second half of September thru 1st of October. This be negative NAO.


Why? What does it mean?
Member Since: July 2, 2009 Posts: 0 Comments: 2811
1495. cg2916
Quoting chevycanes:

that quikscat was from early this morning.

it was from 3:12 PM EST.
Quoting canesrule1:
It' closed its just very elongated.

Now that you mention it, it is. It does still need to tighten the circulation and build and organize convection.
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1494. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 6213
1493. java162
Quoting IKE:


?

Pessimistic.

Pretending? I could care less if it develops.


well then this blog is not for you.
Member Since: Posts: Comments:
1490. Drakoen
Let's hope this does not happen as the CFS forecast for the second half of September thru 1st of October. This be negative NAO.
Member Since: October 28, 2006 Posts: 57 Comments: 30727
guys can we may be watch what we post in here the Admins will be baning we are in a active periods of hurricane season right now with 90L



so TampaSpin may want to re move that photo or he may end up being ban for 24hr that photo is not posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself.


am sure its find if we dont have any thing too talk about but its not find right now
Member Since: Posts: Comments:
Quoting Ameister12:
Poll Time!!!

Do you think ex-TD2 is going become a depression again?

A) Yes
B) No
C) Maybe

NO
Member Since: Posts: Comments:
I still say we need to keep a close eye on the Caribbean wave as it approaches the GOM - lots of moisture, low sheer and hot water to work with....
Member Since: Posts: Comments:

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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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