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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368. wunderkidcayman
9:47 PM GMT on September 25, 2009
Synoptic Time Latitude Longitude Intensity
200909251800 16.1 -31.1 30
Member Since: June 13, 2009 Posts: 2 Comments: 12147
367. wunderkidcayman
9:46 PM GMT on September 25, 2009
25/1145 UTC 15.5N 30.1W T1.5/1.5 99L -- Atlantic
Member Since: June 13, 2009 Posts: 2 Comments: 12147
366. zebralove
9:46 PM GMT on September 25, 2009
just had a nice little rain storm in spring hill fl. Lasted about 10 min. I just love these storms with the sheeting rain it is so amazing to watch the awesome power of intense rain.
Member Since: July 27, 2009 Posts: 3 Comments: 95
365. wunderkidcayman
9:45 PM GMT on September 25, 2009
BEGIN
NHC_ATCF
invest_al082009.invest
FSTDA
R
U
040
010
0000
200909251854
NONE
NOTIFY=ATRP
END
EIGHT, AL, L, , , , , 08, 2009, TD, R, 2009092506, 9999999999, , , , , , WARNING, 3, AL082009

AL, 08, 2009092518, , BEST, 0, 161N, 311W, 30, 1008, TD, 34, NEQ, 0, 0, 0, 0, 1012, 125, 20, 0, 0, L, 0, , 0, 0, EIGHT, M,
Member Since: June 13, 2009 Posts: 2 Comments: 12147
364. wunderkidcayman
9:41 PM GMT on September 25, 2009
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 25 SEP 2009 Time : 211500 UTC
Lat : 16:25:29 N Lon : 31:38:29 W


CI# /Pressure/ Vmax
2.1 /1008.2mb/ 31.0kt


Final T# Adj T# Raw T#
(3hr avg)
2.1 2.2 3.4

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : -14.0C Cloud Region Temp : -32.6C

Scene Type : SHEAR (0.04^ TO DG)

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : 0.2T/hour
Weakening Flag : OFF
Rapid Dissipation Flag : OFF
Member Since: June 13, 2009 Posts: 2 Comments: 12147
362. hydrus
9:31 PM GMT on September 25, 2009
Quoting largeeyes:
This is definitely one of those storms that if it weren't for satelites, we'd never know had existed.
One of many.
Member Since: September 27, 2007 Posts: 1 Comments: 21414
361. largeeyes
9:29 PM GMT on September 25, 2009
This is definitely one of those storms that if it weren't for satelites, we'd never know had existed.
Member Since: August 22, 2006 Posts: 0 Comments: 1455
360. Stormchaser2007
9:28 PM GMT on September 25, 2009
Looks like another long lived system.

FORECAST POSITIONS AND MAX WINDS

INITIAL 25/2100Z 16.4N 31.6W 30 KT
12HR VT 26/0600Z 17.3N 33.1W 35 KT
24HR VT 26/1800Z 18.4N 35.0W 35 KT
36HR VT 27/0600Z 19.8N 36.8W 30 KT
48HR VT 27/1800Z 21.4N 38.1W 25 KT
72HR VT 28/1800Z 24.0N 39.5W 20 KT...REMNANT LOW
96HR VT 29/1800Z...DISSIPATED
Member Since: June 9, 2007 Posts: 4 Comments: 15921
359. Santamaria
9:27 PM GMT on September 25, 2009
@atmoaggie. That's not a bad summary there although there are one or two things that need to be clarified.

1) The industrial revolution was sparked by the realisation that energy to turn things could be obtained by burning coal. Later, you yanks came along and gave us a more streamlined, mass source of energy in the form of oil. Burning that stuff releases carbon dioxide. It was put there by photosynthesis millions of years ago and now we decided to release it in pursuit of our dreams. We started to measure the CO2 in the air at Muana Loa and today we have 385 ppm, that's 385 molecules of CO2 for every million molecules of the rest of the atmospheric gases. Why is that fraction of CO2 so important? Because it allows shortwave radiation from the sun to pass through unimpeded but stops the longwave radiation back from a warmed Earth to escape into cold space. Bit like a blanket. More CO2, thicker the blanket. Mmmm.. it's getting warm in here.

2) When we want to measure something as variable as the weather so we can talk about climate we need a sufficiently long interval to sort out trends from variability. 30 years is the standard for climate trends. We have measurements over longer periods, the Central England series for example that goes back to 1660. Yes, I know, thermometers were crude then but we are only looking for trends remember, not absolutes.

3) Measurement effects are a feature of any measurement: you and I asked to read a thermometer will often end up either rounding up or rounding down, so we might get different figures, but over a long period of time, we'll get a pretty accurate measure of the temperature between us. Don't let the measurement controversy blind you to the trends, remember, we are not dealing in absolutes.

4) Absolutely spot on.

5) We know and learn more each day about the interconnection between climate events. We know on this blog that El Niño affects hurricane development and tracks. And moreover, that those tracks are modelled with less or greater accuracy, depending upon the variables we plug in. The European Centre seems to have a good handle on hurricane tracking at the moment.

6) Again absolutely spot on; we are doing an experiment with this planet and we have no idea about the result, only that it looks shaky.

7) We have the skillls to model weather, hurricanes and climate. All are in the process of being constantly improved.

8) Water vapour is one of the major feedback mechanisms. We know all about that. Warmer oceans, more water vapour, more water vapour, more warming therefore warmer oceans.........

Feedbacks are the big unknowns, we have never been here before although we have seen similar situations where climate events have changed rapidly, e,g, 8.2 ky event. Some think that methane is the big one waiting in the wings.

9) Next year we will have an updated IPCC report, however recent climate events have overtaken the last one already so it's happening faster than we thought.

10) And have a look at this.

http://www.youtube.com/watch?v=AE6Kdo1AQmY&feature=channel

Thanks for reading this far.
358. BahaHurican
9:20 PM GMT on September 25, 2009
Quoting Elena85Vet:


TD8 could isolate the wave behind it from dry air as well?
Possible.
Member Since: October 25, 2005 Posts: 19 Comments: 22318
357. KoritheMan
9:20 PM GMT on September 25, 2009
TD8/Grace is remarkably similar to Ernesto in 1994, track-wise.

Ernesto:



TD8:



Same general steering pattern as well, along with the same time of the year.
Member Since: March 7, 2007 Posts: 583 Comments: 20821
355. tornadodude
9:17 PM GMT on September 25, 2009
Quoting Orcasystems:




sorry, it was just so funny to me I guess lol
Member Since: June 28, 2006 Posts: 25 Comments: 8358
354. BahaHurican
9:17 PM GMT on September 25, 2009
Quoting KerryInNOLA:
Also I am worried that a 500 mph hypercane might form if a meteor hits the ocean and boils the water. I saw this on Discovery channel. We are overdue. Last hypercane hit 60 million yr ago. helped wipe out dinosaurs.
Don't worry about it, kerry. If it happens, there's a good chance u won't know what hit u. Literally.
Member Since: October 25, 2005 Posts: 19 Comments: 22318
353. Orcasystems
9:17 PM GMT on September 25, 2009


AOI

AOI

AOI

AOI
Member Since: October 1, 2007 Posts: 81 Comments: 26511
352. Orcasystems
9:16 PM GMT on September 25, 2009
Quoting tornadodude:


StormTop, post 483


Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting JRRP:

that is what i think... say that in sep is not intelligent

what about oct and nov plus this year is full of suprises
Member Since: June 13, 2009 Posts: 2 Comments: 12147
Quoting BahaHurican:
Thanks. Someone was saying last night that they thought we'd have orange for 2 a.m., but I'm not surprised NHC waited until 8.

Looking at the satpics last night, I didn't realize how high this system was. I have to admit I give the wave behind it more of a chance simply because it's lower, meaning it has a slight chance of avoiding enough of the shear to make it across the ATL and into slightly more favorable conditions.


TD8 could isolate the wave behind it from dry air as well?
Member Since: August 18, 2008 Posts: 0 Comments: 628
he guys do you think that Link will happen with TD#8 and the wave asuming that the wave will develop
Member Since: June 13, 2009 Posts: 2 Comments: 12147
Quoting JupiterFL:


Email me instead of posting on the blog so I don't have to split it with Stormtop.


StormTop, post 483
Member Since: June 28, 2006 Posts: 25 Comments: 8358
345. JRRP
Quoting wunderkidcayman:

if it is then what the hell is TD8 doing in the east atlantic or anywhere look I say it will be over on the 30 of nov or early dec :)

that is what i think... say that in sep is not intelligent
Member Since: Posts: Comments:
Just poking wunderkid. ;)
Member Since: September 9, 2008 Posts: 6 Comments: 3414
Quoting wunderkidcayman:

if it is then what the hell is TD8 doing in the east atlantic or anywhere look I say it will be over on the 30 of nov or early dec :)


Early Dec? I still have a shot at my 16-2-2!
Member Since: September 9, 2008 Posts: 6 Comments: 3414
Quoting wunderkidcayman:

LOL!!!!!!! I am working on it


Email me instead of posting on the blog so I don't have to split it with Stormtop.
Member Since: Posts: Comments:
iceman - you missed the memo. TD08 now. :)
Member Since: September 9, 2008 Posts: 6 Comments: 3414
338. JRRP
i´m out
go to the uni
Member Since: Posts: Comments:
Quoting JRRP:

no remember the season is over :P

if it is then what the hell is TD8 doing in the east atlantic or anywhere look I say it will be over on the 30 of nov or early dec :)
Member Since: June 13, 2009 Posts: 2 Comments: 12147
Quoting Elena85Vet:


The 2am was yellow

The 8am to orange
Thanks. Someone was saying last night that they thought we'd have orange for 2 a.m., but I'm not surprised NHC waited until 8.

Looking at the satpics last night, I didn't realize how high this system was. I have to admit I give the wave behind it more of a chance simply because it's lower, meaning it has a slight chance of avoiding enough of the shear to make it across the ATL and into slightly more favorable conditions.
Member Since: October 25, 2005 Posts: 19 Comments: 22318
Quoting iceman55:
hey all!

Hi iceman what up with you on this wonderful great (and all the words that means the same thing) day
Member Since: June 13, 2009 Posts: 2 Comments: 12147
Quoting KerryInNOLA:
If TD8 can organize it should take a west course into the Carribean and blow up. Then who knows, a cat 5 maybe in the Gulf. After all shear is down, the MJO is comming and the NAO is on it heels.


well there we have it, any other utter destruction coming?
Member Since: June 28, 2006 Posts: 25 Comments: 8358
Quoting iceman55:
hey all!
.
Member Since: September 27, 2007 Posts: 1 Comments: 21414
Quoting BahaHurican:
After a quick look at the imagery, I think I agree with you.

And from the discussion, it looks like NHC isn't giving our current TD much of a chance to get to the G in the alphabet. By tomorrow they expect it to be basically gone, name or no name. I don't think this is likely to be a westward drifter like the storm whose name shall remain uncalled....


well they do forecast this to become Grace
326. JRRP
Quoting wunderkidcayman:
hi guys I knew we would have TD#8 today and we may have more than TD#8 to deal with

no remember the season is over :P
Member Since: Posts: Comments:
Quoting JupiterFL:


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

LOL!!!!!!! I am working on it
Member Since: June 13, 2009 Posts: 2 Comments: 12147
Quoting CybrTeddy:
Personally, I'm more interested about the wave behind TD8.
After a quick look at the imagery, I think I agree with you.

And from the discussion, it looks like NHC isn't giving our current TD much of a chance to get to the G in the alphabet. By tomorrow they expect it to be basically gone, name or no name. I don't think this is likely to be a westward drifter like the storm whose name shall remain uncalled....
Member Since: October 25, 2005 Posts: 19 Comments: 22318
Quoting iceman55:
hey all!


hey iceman
Member Since: June 28, 2006 Posts: 25 Comments: 8358
Quoting iceman55:
hey all!


hi ice
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Quoting hydrus:
And Maine and Alaska.............with power...


oh yes, forgot about them
Member Since: June 28, 2006 Posts: 25 Comments: 8358
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?
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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