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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If iceman is still up I think he would be able to confirm this
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Then in 1982 Alberto did fizzle out but that was after it was affected by derakie in yovan there. But in that case it didnt last the entire hurricane season
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..."Your the Storm"..
Member Since: July 3, 2005 Posts: 414 Comments: 125418
That eye is so tight it's getting me excited!
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Allen 08 aug 1980 1332Z N6.jpg





Media in category "Hurricane Allen"
Member Since: July 3, 2005 Posts: 414 Comments: 125418
Remember when Hurricane Alicia did the chickamahallamachoya back in 1983 in the Gulf of Mexico? Again, the first storm of the yr and that was during a Elnino season. That just proves it right there again!
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Member Since: July 3, 2005 Posts: 414 Comments: 125418
Quoting KoritheMan:


Actually, Allen's winds reached 190 mph, not 170.


Your both wrong peak winds were 185mph at one point with gusts to 210. But it always seems to be the first storm of the season that Revens ekin flow up in alt for yovan. Doesnt seem that way?
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Member Since: July 3, 2005 Posts: 414 Comments: 125418
All NOAA Tropical Imagery Floaters
Member Since: July 3, 2005 Posts: 414 Comments: 125418
Quoting btwntx08:

it was at 190 mph also it didn't hit brownsville it hit just north in kenedy county


Coincidentally, 1999's Bret also struck Kennedy County.
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Quoting cchsweatherman:
Since I'll be taking the weekend off from forecasting, just wanted to say have a nice weekend to everyone. It doesn't appear Tropical Depression 8 will be a threat.


TD8 looks rather ragged at the moment, even though convection has been on the increase. None of the convection is organized, which is what is important.

In any case, good evening to you.
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Quoting kuppenskup:
I dont know if ya'all remember Hurricane Allen back in 1980 when top winds reached 170mph when it became a susener for derakie before it his Brownsville Texas


Actually, Allen's winds reached 190 mph, not 170.
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Since I'll be taking the weekend off from forecasting, just wanted to say have a nice weekend to everyone. It doesn't appear Tropical Depression 8 will be a threat.
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I dont know if ya'all remember Hurricane Allen back in 1980 when top winds reached 170mph when it became a susener for derakie before it his Brownsville Texas
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Interesting feature coming in under the radar.

12N 40W






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Without looking at satellite imagery, I can say with a reasonable degree of certainty, based upon my own experiences tracking tropical cyclones, that at nighttime, when only infrared satellite imagery is available, that it can be quite difficult to pinpoint a definite center within a tropical cyclone. Hence, the illusion of a particular direction of movement appears readily apparent, when in reality, it is not.

This is typically why the NHC waits until visible satellite imagery to designate a system a tropical cyclone; finding a center is more than a little difficult using infrared imagery.
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Iceman-or do you expect TD#8 to do a chickamahallamachoya like Dennis did in 1981?
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Quoting iceman55:
i was looking at SATELLITE images that why i said head west.


So you mean for now not for the long track right?
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Iceman, I had to log out earlier so I didnt see your response, why do you say TD # 8 will head west?
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Quoting hunkerdown:
can I get my jerry beads :)


'Fraid we don't want to go there...
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You know what you have to do for Jerry beads...
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Looks like it's holding it's own to me!! PLEASE stop arguing over a TD!!!!
Quoting Bordonaro:

The system just off the CV Islands is in the European Sat pic, IS NOT TD 8!! TD 8 is to it's NW!! PLUS the pic I posted shows convection firing up on TD *!!
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Quoting KoritheMan:


I'm just messin. :P
can I get my jerry beads :)
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Quoting hunkerdown:
caution, you may join us with the Springer image


I'm just messin. :P
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LOOKS LIKE IT'S HOLDING IT'S OWN!!
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Quoting JLPR:


nothing else to say tonight

im off to hear some music =P


Other than TD8 looks horrible? :P
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625. JLPR


nothing else to say tonight

im off to hear some music =P
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Quoting btwntx08:

lol


:D
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Quoting KoritheMan:


You mean this one?

caution, you may join us with the Springer image
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GUYS PLEASE STOP FIGHTING!!!!!!!!!
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LOL...me thinks the Iceman is posting through spirit laced glasses. I'd post an image, but I wouldn't know what beer to give credit to....
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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.