New tropical depression could form off the coast of Africa

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

Share this Blog
1
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 419 - 369

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15Blog Index

Quoting BahaHurican:
I really can't get over the LBAR outperforming any model on any storm.... lol.... used to be the laughingstock of the models, as in, if the LBAR was pointed in one direction, one could count on the storm going in the complete opposite.... lol


and the wierd thing is. Though Erika SW jog was due to center relocation and not continuing motion, it did predict that Erika would dip SW and then continue W.
Member Since: Posts: Comments:
Quoting Weather456:


very true. The LBAR out performing all models on Erika's track and LGEM outperformed with Fred's intensity.
I really can't get over the LBAR outperforming any model on any storm.... lol.... used to be the laughingstock of the models, as in, if the LBAR was pointed in one direction, one could count on the storm going in the complete opposite.... lol
Member Since: October 25, 2005 Posts: 19 Comments: 21392
Quoting timtrice:
The system was clearly weakening. I'm well aware they dont' write these things up within five minutes before release. But they don't write it based off what happened two hours ago, either. They write them based off the whole picture and the whole picture clearly says the system is not looking better by any means. TD 8 didn't just drop convection in the last 30 minutes or hour. It's been a 8-hour long process. The system hasn't looked good for a long time.

I can't tell you how many times i've seen the NHC watch something spur up and wait for sustained convection. The convection comes but then begins to dissipate. So, no advisory. Anyone who's studied these systems on a regular basis knows this. And typically the trends they look for last for about 24 hours. But, sometimes they don't and still get upgraded. They don't follow one specific rule which - if you go by there standards - a tropical depression must maintain convection for a period of 24 hours. You'er going to tell me this meets that standard? BS

You may have me on Pakistan cause I don't follow Indian cyclones. But the JTWC and Australia wouldn't pull this.

Well, I wasn't able to watch the system today while at work, so I came in on TD 8 after its renumbering. At that time, it looked sufficiently well organized to me to justify the NHC's call. You may have the right of it on the current weakening trend; I still don't agree with you that the comment about looking better is a wrong call and "slap-in-the-face" type comment. I guess because the last time I looked at it was last night, NHC's call looked pretty logical to me. However, ymmv...
Member Since: October 25, 2005 Posts: 19 Comments: 21392
It rarely gets under 50 degrees in Miami, so now living in Tallahassee I'm gonging to have to contend with that for four months.
Member Since: Posts: Comments:
Quoting Weather456:



lol, do you guys know, I've been visited by cold fronts. The nights do get cold relative to what we normally feel. 17C is cold to me.


Living in Miami, though I am in college now and not there. I understand what you mean.
Member Since: Posts: Comments:
Quoting BahaHurican:
Looks like NHC is following statisticals, then. Not surprising, given the statistical models' comparatively high rate of accuracy compared to the dynamics this year....


very true. The LBAR out performing all models on Erika's track and LGEM outperformed with Fred's intensity.
Member Since: Posts: Comments:
Quoting Weather456:
Funny thing...

with the exception of the CMC...

dynamical models weaken TD 8 while the statistical ones are the ones that bring TD 8 to Grace.
Looks like NHC is following statisticals, then. Not surprising, given the statistical models' comparatively high rate of accuracy compared to the dynamics this year....
Member Since: October 25, 2005 Posts: 19 Comments: 21392
Quoting ElConando:


How cold does it get where you are? mid 60's?


since I've been interested in weather in 1998, the coldest temperature I ever saw was in February of 2008 when we were blasted by several cold air masses. The lowest temperature I got was 16C, and thats way too cold to what we normally see at nights - 25C.
Member Since: Posts: Comments:
Quoting KoritheMan:


Correct me if I'm wrong, but even during the winter, St. Kitts is predominantly warm, is it not?

Bearing that in mind, it seems that any relief winter could potentially provide will be quite brief, and relatively infrequent.



lol, do you guys know, I've been visited by cold fronts. The nights do get cold relative to what we normally feel. 17C is cold to me.
Member Since: Posts: Comments:
Quoting Weather456:


was referring to the cool season but using the winter period.


How cold does it get where you are? mid 60's?
Member Since: Posts: Comments:
Quoting ElConando:


winter? there is such a thing where you live?

yes there is but it not like up north the cold fronts have cold rain instead of snow the winds also get cool
Member Since: June 13, 2009 Posts: 2 Comments: 10891
Quoting ElConando:


winter? there is such a thing where you live?


was referring to the cool season but using the winter period.
Member Since: Posts: Comments:
Quoting Weather456:


well hot and dry. I dont like cold weather but I'm actually looking forward to winter, lol


Correct me if I'm wrong, but even during the winter, St. Kitts is predominantly warm, is it not?

Bearing that in mind, it seems that any relief winter could potentially provide will be quite brief, and relatively infrequent.
Member Since: Posts: Comments:
Funny thing...

with the exception of the CMC...

dynamical models weaken TD 8 while the statistical ones are the ones that bring TD 8 to Grace.
Member Since: Posts: Comments:
Quoting Weather456:


Fred had an anticyclone over it. If shear was able defeat a powerful 125 mph cat 3, it can sure make easy work of a TD/TS.

ok but it did not last long but this one might I am saying if it dose get it
Member Since: June 13, 2009 Posts: 2 Comments: 10891
Quoting ElConando:


From reading your blog I see what you mean about the African wave, could sneak into the Eastern Atlantic.
Quoting Weather456:


well hot and dry. I dont like cold weather but I'm actually looking forward to winter, lol


winter? there is such a thing where you live?
Member Since: Posts: Comments:
Well, well, well!! TD 8 has been born!!

According to the NHC, its life will be REAL SHORT!! I have the UTMOST respect for ALL the NHC forecasters!! They work HARD and do an AWESOME job!!

SOME PLEASE give these folks some REAL good supercomputers to model with!! I know that NOAA just finished upgrading their systems, but they're doing a HORRIBLE job predicting anything in the Tropics, except for Bill!!!
Member Since: Posts: Comments:
Quoting wunderkidcayman:

good evening to you too weather456 what up with you on the other side of the caribbean


well hot and dry. I dont like cold weather but I'm actually looking forward to winter, lol
Member Since: Posts: Comments:
Quoting wunderkidcayman:

well if TD8/pre-grace can get a nice anticyclone over it it shall not have a problem with shear which would not let it last long if it dosen't


The models do not even hint at an anticyclonic environment.
Member Since: Posts: Comments:
Quoting Weather456:
From my update today, still valid

This feature is moving off towards the west-northwest under the influence of the Azores high-pressure ridge. This motion is expected through the next 3-5 days until a trough digs across the area and creates a weakness in the ridge, causing the storm to take a more northward motion. Track guidance beyond 5 days becomes uncertain due to the intensity uncertainty so the feature will be monitored.


From reading your blog I see what you mean about the African wave, could sneak into the WESTERN Atlantic.
Member Since: Posts: Comments:
Quoting Weather456:
Good evening folks

good evening to you too weather456 what up with you on the other side of the caribbean
Member Since: June 13, 2009 Posts: 2 Comments: 10891
Quoting wunderkidcayman:

well if TD8/pre-grace can get a nice anticyclone over it it shall not have a problem with shear which would not let it last long if it dosen't


Fred had an anticyclone over it. If shear was able defeat a powerful 125 mph cat 3, it can sure make easy work of a TD/TS. Also all this was predicted.
Member Since: Posts: Comments:
From my update today, still valid

This feature is moving off towards the west-northwest under the influence of the Azores high-pressure ridge. This motion is expected through the next 3-5 days until a trough digs across the area and creates a weakness in the ridge, causing the storm to take a more northward motion. Track guidance beyond 5 days becomes uncertain due to the intensity uncertainty so the feature will be monitored.
Member Since: Posts: Comments:
Quoting timtrice:
The system was clearly weakening. I'm well aware they dont' write these things up within five minutes before release. But they don't write it based off what happened two hours ago, either. They write them based off the whole picture and the whole picture clearly says the system is not looking better by any means. TD 8 didn't just drop convection in the last 30 minutes or hour. It's been a 8-hour long process. The system hasn't looked good for a long time.

I can't tell you how many times i've seen the NHC watch something spur up and wait for sustained convection. The convection comes but then begins to dissipate. So, no advisory. Anyone who's studied these systems on a regular basis knows this. And typically the trends they look for last for about 24 hours. But, sometimes they don't and still get upgraded. They don't follow one specific rule which - if you go by there standards - a tropical depression must maintain convection for a period of 24 hours. You'er going to tell me this meets that standard? BS

You may have me on Pakistan cause I don't follow Indian cyclones. But the JTWC and Australia wouldn't pull this.



wait 10 hours
Member Since: Posts: Comments:
Quoting BahaHurican:
They made a good call on Fred in the same area.... but to argue your side, Fred developed quickly to a major. If this doesn't, models may not get as good a handle. Even if it goes more west than forecast, it doesn't look to last long as a TS.....

well if TD8/pre-grace can get a nice anticyclone over it it shall not have a problem with shear which would not let it last long if it dosen't
Member Since: June 13, 2009 Posts: 2 Comments: 10891
The system was clearly weakening. I'm well aware they dont' write these things up within five minutes before release. But they don't write it based off what happened two hours ago, either. They write them based off the whole picture and the whole picture clearly says the system is not looking better by any means. TD 8 didn't just drop convection in the last 30 minutes or hour. It's been a 8-hour long process. The system hasn't looked good for a long time.

I can't tell you how many times i've seen the NHC watch something spur up and wait for sustained convection. The convection comes but then begins to dissipate. So, no advisory. Anyone who's studied these systems on a regular basis knows this. And typically the trends they look for last for about 24 hours. But, sometimes they don't and still get upgraded. They don't follow one specific rule which - if you go by there standards - a tropical depression must maintain convection for a period of 24 hours. You'er going to tell me this meets that standard? BS

You may have me on Pakistan cause I don't follow Indian cyclones. But the JTWC and Australia wouldn't pull this.

Quoting BahaHurican:
My first response to this was "huh???"

But Tim, NHC's 5 p.m. has to be based on data from BEFORE now, because it has to come out at 5 p.m. Therefore their comment is directed towards imagery that is at least 4-5 hours old now. And at that time the storm DID (as u said) look much better. Along with that, there is a matter of persistance which is operationally expected with TDs in order for initial classification to take place. I don't see why u are so irate.
Member Since: Posts: Comments:
Good evening folks
Member Since: Posts: Comments:
Is it just me or besides a few people this room is full of bloggers that make this a bi**hfest continually. Often criticizing the NHC and even Dr Masters.
I wonder if it's because so many wishcasters are completely frustrated that this season hasn't gone their way. That they have no storms to points towards them. I mean come on folks....

Ugggggggg... sorry ....

We need more Weather456's, Orca's, Tampa's, StormW's and less of ... well you name them
Member Since: Posts: Comments:
Quoting Elena85Vet:


I think it depends on whether it holds together thru shear and stays weak. Most storms this year have taken more of a westward track than projected with the exception of Fred which became a cane early.


Even the shallow layer steering dictates a pronounced poleward motion. This is a fish storm.
Member Since: Posts: Comments:
Quoting Canekid98:
tropical depression grace could possibly follow a westerly current into a hot spot with low shear and high ssts the carribean. the models are starting to pick up on it

wow what model is that you are referring to
Member Since: June 13, 2009 Posts: 2 Comments: 10891
Quoting wunderkidcayman:

I think you are right plus the models overall has been bad all year so guys in the western atlantic and that includes the caribbean should watch this TD#8


I think it depends on whether it holds together thru shear and stays weak. Most storms this year have taken more of a westward track than projected with the exception of Fred which became a cane early.
Member Since: August 18, 2008 Posts: 0 Comments: 628
Quoting wunderkidcayman:

I think you are right plus the models overall has been bad all year so guys in the western atlantic and that includes the caribbean should watch this TD#8
They made a good call on Fred in the same area.... but to argue your side, Fred developed quickly to a major. If this doesn't, models may not get as good a handle. Even if it goes more west than forecast, it doesn't look to last long as a TS.....
Member Since: October 25, 2005 Posts: 19 Comments: 21392
Not quite closed off to the SW.

I think there's a few TS barbs in there, too (colorblind).

Large Image
Member Since: September 9, 2008 Posts: 6 Comments: 3414
385. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Warning #2
TROPICAL DEPRESSION "20"
6:00 AM JST September 26 2009
================================

Subject: Tropical Depression In Sea East Of The Philippines

At 21:00 PM UTC, Tropical Depression (994 hPa) located at 15.2N 122.7E has 10 minute sustained winds of 30 knots with gusts of 45 knots. The depression is reported as moving west at 17 knots

RSMC Dvorak Intensity:

Forecast and Intensity
=====================
24 HRS: 15.9N 116.7E - 35 kts (CAT 1/Tropical Storm)
Member Since: Posts: Comments:
Quoting timtrice:
It has nothing to do with whether it's going to be a threat to anyone and everything to do with the inconsistencies of the NHC. The same way they handled the Jersey storm which most meteorologists I've spoken to believed was at least a subtropical system. The NHC told me why they didn't upgrade it. Fine. But, what's with the delay on this one? It's one thing to say you've seen something that now confirms the system is a depression. But to say it's developed enough convection when clearly convection is weakening? Give me a freaking break.

It's about inconsistencies. In no other basin worldwide are the warning centers so inconsistent with how they classify systems. Pathetic.

Again, u have to know that the discussion was written around 4 p.m. EDT, which is a couple hours ago, based on imagery that is older than that. When I looked at TD 8 myself, it still looked pretty good. What they said is absolutely true. I also don't agree with u about inconsistency in classification, because I have seen some real doozies by the Indian Met office, especially on the Pakistan side....
Member Since: October 25, 2005 Posts: 19 Comments: 21392
Quoting MiamiHurricanes09:
if 1010-1000 MSLP steering currents is correct, then the NHC cone is 0% accurate. If the currents are correct 08L should continuw west and then curve out to sea at around 65W. It can also possibly follow a different current and end up in the caribbean...is there something that models are seeing that I'm not?


I think you are right plus the models overall has been bad all year so guys in the western atlantic and that includes the caribbean should watch this TD#8
Member Since: June 13, 2009 Posts: 2 Comments: 10891
Quoting timtrice:
I am irate! How in the world is the NHC going to say on the first advisory now the system has developed enough convection to warrant classification when the system looked MUCH better 8 hours ago? This is a slap in the face from the know-it-alls at the NHC telling everyone else that we wouldn't know a tropical depression from a blizzard if it bit us in the ARSE.

Unbelievable...
My first response to this was "huh???"

But Tim, NHC's 5 p.m. has to be based on data from BEFORE now, because it has to come out at 5 p.m. Therefore their comment is directed towards imagery that is at least 4-5 hours old now. And at that time the storm DID (as u said) look much better. Along with that, there is a matter of persistance which is operationally expected with TDs in order for initial classification to take place. I don't see why u are so irate.
Member Since: October 25, 2005 Posts: 19 Comments: 21392
tropical depression grace could possibly follow a westerly current into a hot spot with low shear and high ssts the carribean. the models are starting to pick up on it
Member Since: Posts: Comments:
It has nothing to do with whether it's going to be a threat to anyone and everything to do with the inconsistencies of the NHC. The same way they handled the Jersey storm which most meteorologists I've spoken to believed was at least a subtropical system. The NHC told me why they didn't upgrade it. Fine. But, what's with the delay on this one? It's one thing to say you've seen something that now confirms the system is a depression. But to say it's developed enough convection when clearly convection is weakening? Give me a freaking break.

It's about inconsistencies. In no other basin worldwide are the warning centers so inconsistent with how they classify systems. Pathetic.

Quoting Nolehead:
372. timtrice 9:55 PM GMT on September 25, 2009
I am irate! How in the world is the NHC going to say on the first advisory now the system has developed enough convection to warrant classification when the system looked MUCH better 8 hours ago? This is a slap in the face from the know-it-alls at the NHC telling everyone else INCLUDING Dr. Masters that we wouldn't know a tropical depression from a blizzard if it bit us in the ARSE.

Unbelievable...



WTH??? Are you so "irate" about?? the system isn't goig to do no harm other than ship traffic for now.....gees drink a beer and chill...
Member Since: Posts: Comments:
378. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Warning #1
TROPICAL DEPRESSION "20"
3:00 AM JST September 26 2009
================================

Subject: Tropical Depression In Sea East Of The Philippines

At 18:00 PM UTC, Tropical Depression (996 hPa) located at 15.1N 123.1E has 10 minute sustained winds of 30 knots with gusts of 45 knots. The depression is reported as moving west at 17 knots

RSMC Dvorak Intensity: N/A

Forecast and Intensity
=====================
24 HRS: 16.4N 117.2E - 35 kts (CAT 1/Tropical Storm)

--------
anyone have a back-up Dvorak Intensity page for the JMA?
Member Since: Posts: Comments:
Quoting timtrice:
I am irate! How in the world is the NHC going to say on the first advisory now the system has developed enough convection to warrant classification when the system looked MUCH better 8 hours ago? This is a slap in the face from the know-it-alls at the NHC telling everyone else that we wouldn't know a tropical depression from a blizzard if it bit us in the ARSE.

Unbelievable...


They calls it likes they sees it.
'Popeye'
Member Since: August 18, 2008 Posts: 0 Comments: 628
if 1010-1000 MSLP steering currents is correct, then the NHC cone is 0% accurate. If the currents are correct 08L should continuw west and then curve out to sea at around 65W. It can also possibly follow a different current and end up in the caribbean...is there something that models are seeing that I'm not?

Member Since: Posts: Comments:
Member Since: Posts: Comments:
372. timtrice 9:55 PM GMT on September 25, 2009
I am irate! How in the world is the NHC going to say on the first advisory now the system has developed enough convection to warrant classification when the system looked MUCH better 8 hours ago? This is a slap in the face from the know-it-alls at the NHC telling everyone else INCLUDING Dr. Masters that we wouldn't know a tropical depression from a blizzard if it bit us in the ARSE.

Unbelievable...



WTH??? Are you so "irate" about?? the system isn't goig to do no harm other than ship traffic for now.....gees drink a beer and chill...
Member Since: Posts: Comments:
373. HadesGodWyvern (Mod)
Philippines Atmospherical Geophysical Astronomical Services and Administration

ical Storm "ONDOY" has accelerated further as it moves closer to Central Luzon.

Tropical Cyclone Bulletin #7
=======================
At 5:00 a.m PhST, Tropical Storm Ondoy located at 15.0ºN 122.5ºE or 130 kms southeast of Baler, Aurora has 10 minute sustained winds of 85 km/h (45 kts) with gusts up to 100 km/h (55 kts).

Signal Warnings
====================

Signal Warning #2 (60-100 km/h)

Luzon region
1.La Union
2.Pangasinan
3.Benguet
4.Nueva Vizcaya
5.Quirino
6.Aurora
7.Nueva Ecija
8.Pampanga
9.Tarlac
10.Zambales
11.Bulacan
12.Northern Quezon
13.Polillo Is.
14.Camarines Norte
15.Rizal

Signal Warning #1 (30-60 km/h)

Luzon region
1.Isabela
2.Mt. Province
3.Ifugao
4.Ilocos Sur
5.Bataan
6.Cavite
7.Laguna
8.Batangas
9.Marinduque
10.Mindoro Provinces
11.Lubang Is.
12.Southern Quezon
13.Camarines Sur
14.Albay
15.Burias Is.
16.Metro Manila

Additional Information
========================
Public Storm Warning Signals elsewhere now lowered.

This disturbance is expected to enhance the Southwest Monsoon and bring rains over Central and Southern Luzon and Visayas. Residents living in low-lying areas and near mountain slopes in areas affected by the Southwest Monsoon and those under signals #1 and #2 are alerted against possible flashfloods and landslides.

Those living along the coast under signal #2 are advised to be on alert against big waves generated by the storm.

The public and the disaster coordinating councils concerned are advised to take appropriate actions and watch for the next bulletin to be issued at 11 A.M. today.
Member Since: Posts: Comments:
I am irate! How in the world is the NHC going to say on the first advisory now the system has developed enough convection to warrant classification when the system looked MUCH better 8 hours ago? This is a slap in the face from the know-it-alls at the NHC telling everyone else that we wouldn't know a tropical depression from a blizzard if it bit us in the ARSE.

Unbelievable...
Member Since: Posts: Comments:
Quoting wunderkidcayman:
25/1145 UTC 15.5N 30.1W T1.5/1.5 99L -- Atlantic


that is from this morning
Quoting Santamaria:
@atmoaggie. That's not a bad summary there although there are one or two things that need to be clarified...Thanks for reading this far.


Thanks santamaria. I love this discussion (I know I'm in the minority there). And now, back to the show...
Member Since: Posts: Comments:

Viewing: 419 - 369

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.