New tropical depression could form off the coast of Africa

By: Dr. Jeff Masters , 1:12 PM GMT on September 25, 2009

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A tropical wave (99L) is located near 15N, 30W, about 300 miles west of the Cape Verdes Islands. This wave has seen an increase in heavy thunderstorm activity this morning, and low-level spiral bands have formed. The system can already be classified as a tropical depression using the satellite-based Dvorak technique. This morning's QuickSCAT pass showed a loose but closed circulation, with top winds of 30 mph in the heaviest thunderstorms. Wind shear is moderate, about 10 - 20 knots. There is a modest amount of dry air to 99L's west that does not appear to be interfering with the storm's organization.


Figure 1. Morning visible satellite image of Invest 99L (left side of image) and a new tropical wave moving off the coast of Africa.

As 99L moves west-northwest over the next two days, sea surface temperatures will cool by 1°C and winds shear will remain in the moderate range. Some dry air may also affect the storm. These conditions give 99L a good chance of forming into a tropical depression, and NHC has given the system a moderate (30 - 50%) chance of developing into a tropical depression by Sunday. By Monday, wind shear will increase to the high range, 20 - 30 knots, and 99L will probably weaken or be torn apart. None of the computer models forecast development of 99L or any other system in the Atlantic over the next seven days.

A new tropical wave with plenty of heavy thunderstorm activity and some spin is moving off the coast of Africa today. This wave is under a moderate amount of wind shear, 10 - 20 knots, and has some potential for development this week as it moves west or west-northwest past the Cape Verdes Islands.

The latest wind shear forecasts from our major computer models show high values of wind shear affecting most of the tropical Atlantic for the next ten days. This is typical for an El Niño year, and it will be difficult for any storms to get to hurricane strength over the next ten days because of the high shear. The latest 16-day GFS forecast predicts wind shear will decline some by the 2nd week of October, though.


Figure 2. Wind shear forecast for Thursday, October 2 at 00 UTC made by last night's 00Z run of the GFS model. Wind shear is expected to be high over most of the tropical Atlantic for the next ten days, including the Caribbean. Wind shear values below 8 m/s (about 15 knots, red colors), are typically needed to support tropical storm formation.

Jeff Masters

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Quoting wunderkidcayman:
hi guys I knew we would have TD#8 today and we may have more than TD#8 to deal with


You are so awesome. Can I have the lottery numbers for tomorrow?
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Quoting tornadodude:


I think it is going to do a couple figure eights and then wipe out NOLA, FL, NYC, and the Carolinas
And Maine and Alaska.............with power...
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hi guys I knew we would have TD#8 today and we may have more than TD#8 to deal with
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Quoting OSUWXGUY:
Deep convection is really falling apart recently...

Better get it back soon or we'll have our second depression of the year not to reach TS strength.

WV Loop


Its DMIN out there, not big deal really
Quoting JRRP:

it is you :P


ah ha thot so lol
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Quoting BahaHurican:
Afternoon, all.

When did NHC go to orange with our latest TC? Was it last night or this a.m.?


The 2am was yellow

The 8am to orange
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313. JRRP
Quoting will40:


Is it me or did it just jog to the west?

it is you :P
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Afternoon, all.

When did NHC go to orange with our latest TC? Was it last night or this a.m.?
Member Since: October 25, 2005 Posts: 19 Comments: 22725
Personally, I'm more interested about the wave behind TD8.
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Quoting hydrus:
T.D. 8 looks stronger than Choi Wan. It could make big waves...J.K.


I think it is going to do a couple figure eights and then wipe out NOLA, FL, NYC, and the Carolinas
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Deep convection is really falling apart recently...

Better get it back soon or we'll have our second depression of the year not to reach TS strength.

WV Loop
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Quoting will40:


Is it me or did it just jog to the west?
T.D. 8 looks stronger than Choi Wan. It could make big waves...J.K.
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Quoting tornadodude:
hey guys,

so, I think TD 8 looks like a 50mph ts, also, Florida is a likely target as well right?
maybe a cat 5?

JK


Is it me or did it just jog to the west?
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hey guys,

so, I think TD 8 looks like a 50mph ts, also, Florida is a likely target as well right?
maybe a cat 5?

JK
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305. JLPR


D-min in action
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Quoting JLPR:


then we both get cookies =P


Yea or split one :-)
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303. JLPR
Quoting will40:


look at post time ours are the same lol


then we both get cookies =P
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302. JLPR
Quoting Dakster:
JLPR - What type of "cookie" do you want?


I would be happy with a chocolate chip one xD
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Quoting JLPR:
ha! I won
do I get a cookie? :)


look at post time ours are the same lol
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300. JLPR
the dry air is still there but it doesn't seem to be affecting 08L

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JLPR - What type of "cookie" do you want?
Member Since: March 10, 2006 Posts: 0 Comments: 10754
296. JLPR
ha! I won
do I get a cookie? :)
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Quoting Dakster:


Will it be a GRACEful transition?


That's so bad...yet so funny. Nice work.
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294. JLPR
Public Advisory Issued

...EIGHTH TROPICAL DEPRESSION OF THE SEASON FORMS OVER THE EASTERN
ATLANTIC...NO THREAT TO LAND...

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291. JRRP
...SUMMARY OF 500 PM AST INFORMATION...
LOCATION...16.4N 31.6W
MAXIMUM SUSTAINED WINDS...35 MPH
PRESENT MOVEMENT...NORTHWEST OR 305 DEGREES AT 14 MPH
MINIMUM CENTRAL PRESSURE...1008 MB

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Hurricane center has 8 now
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289. JLPR
000
WTNT23 KNHC 252032
TCMAT3
TROPICAL DEPRESSION EIGHT FORECAST/ADVISORY NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082009
2100 UTC FRI SEP 25 2009

TROPICAL DEPRESSION CENTER LOCATED NEAR 16.4N 31.6W AT 25/2100Z
POSITION ACCURATE WITHIN 25 NM

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Quoting OSUWXGUY:


I'm not sure how much they use the AMSU yet... Still being tweaked...more of a beta version at the moment. I bet we see a depression and then storm if we get more deep convection firing this evening.


Will it be a GRACEful transition?
Member Since: March 10, 2006 Posts: 0 Comments: 10754
Quoting BurnedAfterPosting:


so this could actually be Grace at 5pm?


I'm not sure how much they use the AMSU yet... Still being tweaked...more of a beta version at the moment. I bet we see a depression and then storm if we get more deep convection firing this evening.
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Quoting mikatnight:
Gotta go get some money. Thanks everyone, back later...


Can you get some for everyone?
Member Since: March 10, 2006 Posts: 0 Comments: 10754
Stormw - as long as it doesn't pull a Wilma...
Member Since: March 10, 2006 Posts: 0 Comments: 10754
Gotta go get some money. Thanks everyone, back later...
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Computer room overheating due to AC issues has created numerous problems, please check all product dates/times while we sift through the debris.


From Navy site never seen that before
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Ok. Just thought I was screwing up on my math (not again!). Yeah you seem a bit high on the numbers there, unless all hell breaks loose (literally).
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Quoting mikatnight:


I have no idea why that comment is in bold type.
Yeah, i get it, but what's wrong with what I said? hmmmm


Nothing wrong. Just clarifying.

I had 16-4-2. Don't have a shot. :)
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In looking at the microwave imagery, it has very nice structure already.

Don't see anything that stops it from becoming Grace.
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Quoting Seastep:
mikatnight - TDs don't count.

It's TS-Cane-Major Cane. :)

Currently 6-2-2


I have no idea why that comment is in bold type.
Yeah, i get it, but what's wrong with what I said? hmmmm
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Listen to Barometer Bob Show on Thursday evening
Listen to Barometer Bob Show on Thursday evening
Listen to Barometer Bob Show on Thursday evening
Listen to Barometer Bob Show on Thursday evening
Listen to Barometer Bob Show on Thursday evening
Ok. Got it. Thanks.
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mikatnight - TDs don't count.

It's TS-Cane-Major Cane. :)

Currently 6-2-2
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Quoting GeoffreyWPB:Atlantic
08L.EIGHT


Hey, same as I got. 8-4-2
I need 2 more named, and 2 minor hurricanes and then I win the WU $1,000,000 pool! So exciting...
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Quoting BurnedAfterPosting:


great read as always this morning, so have you gotten a chance to see if anything has changed with the area of disturbed weather over the Yucatan?

Not that I want to pretend to be StormW, but I see surface lows out there. Luckily, land will take care of them...


(Best seen full size in new window...click here)
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271. JRRP
mmm??
editado
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Quoting StormW:


great read as always this morning, so have you gotten a chance to see if anything has changed with the area of disturbed weather over the Yucatan?
Hi StormW!
You know I meant to call the last time you were on the BB show and ask both of you guys about that darned Hebert box, and then forgot to listen in. You going back on the show anytime soon?
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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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