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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469. Skyepony (Mod)
Harbor cam from the fray in the Philippines..

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 25 SEP 2009 Time : 233000 UTC
Lat : 15:05:00 N Lon : 124:03:28 E


CI# /Pressure/ Vmax
2.4 / 997.6mb/ 34.0kt


Final T# Adj T# Raw T#
(3hr avg)
2.3 2.5 2.7

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : -10.3C Cloud Region Temp : -25.8C

Scene Type : CURVED BAND with 0.42 ARC in DK GRAY
Maximum CURVED BAND with 0.68 ARC in DK GRAY
at Lat: 15:40:48 N Lon: 123:26:59 E

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : WEST PACIFIC
Dvorak CI > MSLP Conversion Used : PACIFIC

Tno/CI Rules : Constraint Limits : 0.7T/6hr
Weakening Flag : ON
Rapid Dissipation Flag : OFF
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Quoting iceman55:
cooling dry air


Lol. We miss out again.


A WEAK COLD FRONT WILL ONCE
AGAIN MOVE SOUTHWARD AND STALL SOMEWHERE OVER THE CWA MONDAY NIGHT
INTO TUESDAY.
..WITH GFS KEEPING THE BOUNDARY INLAND BUT ECMWF
TAKING IT WELL INTO THE COASTAL WATERS. FOR NOW WENT WITH A BLEND
OF THE TWO FOR TEMPERATURES. FRONT WILL SHIFT BACK NORTHWARD
WEDNESDAY INTO THURSDAY AS AN UPPER LEVEL RIDGE BRIEFLY BUILDS
OVER THE WESTERN GULF WITH DEEPER MOISTURE RETURNING TO THE
FORECAST AREA AND THUS HIGHER PRECIP CHANCES. GLOBAL MODELS STILL
SUGGEST A STRONG COLD FRONT WILL APPROACH THE FORECAST AREA
SOMETIME TOWARDS THE END OF THE WEEK...BUT STALL SOMEWHERE IN OR
NEAR THE CWA AS THE UPPER LEVEL TROUGH SHOVING THE BOUNDARY
SOUTHWARD DOES NOT APPEAR AS STRONG OR DEEP AS IN PREVIOUS RUNS.
DUE TO THE UNCERTAINTY WILL KEEP POPS ON THE LOW SIDE AND NOT GO
OVERBOARD ON A COOLDOWN JUST YET.


Lol. I think someone is getting tired of the hot and stickys. Cold front and stall will be in our forecast for the next 8 months. :) We get lucky once in a while.
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by mon oct 5 even stronger surge of cooler air setting up with two big systems shown in epac with the strongest coming up over baja mex setting the stage for the first of big fall storms
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466. Skyepony (Mod)
17W

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Quoting iceman55:
when i was gonna work this morning feeling Littlite cool.here ing slidell la.


forecasted lows for thu oct 1 09 N.A. view
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575

WHXX04 KWBC 252315

CHGQLM

ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL DEPRESSION EIGHT 08L



INITIAL TIME 18Z SEP 25



DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT

REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD

NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC

OFFICIAL FORECAST.





FORECAST STORM POSITION



HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)



0 15.9 31.5 305./12.0

6 16.5 32.5 301./11.9

12 17.2 34.2 292./17.3

18 17.9 35.4 298./13.4

24 18.5 36.6 295./13.0

30 19.2 37.7 305./12.9

36 20.2 38.3 329./11.0

42 20.4 39.7 281./13.2



STORM DISSIPATED AT 42 HRS AT THE ABOVE PSN.
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159

WHXX01 KWBC 260016

CHGHUR

TROPICAL CYCLONE GUIDANCE MESSAGE

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

0016 UTC SAT SEP 26 2009



DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE

AND SUBTROPICAL CYCLONE INFORMATION.



ATLANTIC OBJECTIVE AIDS FOR



TROPICAL CYCLONE EIGHT (AL082009) 20090926 0000 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

090926 0000 090926 1200 090927 0000 090927 1200



LAT LON LAT LON LAT LON LAT LON

BAMS 17.0N 31.8W 19.4N 34.4W 21.7N 35.8W 23.5N 36.6W

BAMD 17.0N 31.8W 18.6N 33.6W 20.3N 34.8W 21.8N 35.1W

BAMM 17.0N 31.8W 18.5N 34.0W 20.1N 35.6W 21.2N 36.6W

LBAR 17.0N 31.8W 18.7N 33.3W 20.5N 34.4W 22.0N 34.9W

SHIP 30KTS 33KTS 36KTS 35KTS

DSHP 30KTS 33KTS 36KTS 35KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

090928 0000 090929 0000 090930 0000 091001 0000



LAT LON LAT LON LAT LON LAT LON

BAMS 25.1N 37.1W 27.9N 36.2W 27.1N 34.0W 23.6N 32.5W

BAMD 22.8N 35.1W 24.1N 35.5W 23.4N 34.9W 21.2N 34.2W

BAMM 22.0N 37.6W 23.5N 39.4W 24.2N 40.0W 23.0N 40.4W

LBAR 22.9N 34.7W 24.2N 33.0W 23.8N 28.8W 23.8N 22.1W

SHIP 37KTS 40KTS 44KTS 51KTS

DSHP 37KTS 40KTS 44KTS 51KTS



...INITIAL CONDITIONS...

LATCUR = 17.0N LONCUR = 31.8W DIRCUR = 310DEG SPDCUR = 12KT

LATM12 = 15.4N LONM12 = 30.0W DIRM12 = 303DEG SPDM12 = 12KT

LATM24 = 14.3N LONM24 = 28.0W

WNDCUR = 30KT RMAXWD = 20NM WNDM12 = 25KT

CENPRS = 1008MB OUTPRS = 1012MB OUTRAD = 125NM SDEPTH = M

RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM



$$

NNNN
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i feel the wind blowin though my doorway
its telling me that the summers gone
and that winter waits in the shadows
waitin with the storm
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#423 850Realtor - I sent you an WU email message telling you how I do it. Hope it helps.
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Really? Where? I could not see it.

Quoting iceman55:
SQUAWK i did .
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U should say where u got things from, ice, but I agree this is just a drama teaser, trying to get some action going in the blog (though not the kind we really need....)

I'm gone for a while... see u later, guys...
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just reading back some things made me laugh LOL


iceman if you are going to cut and paste someone else's work, you should give them credit.

copied from this page at CSU

Quoting iceman55:
Dakster .Using the AMSU-derived azimuthally averaged temperature and height files radial/height cross sections of temperature and tangential wind are created (see Demuth et al (2004) ). The tangential wind field is derived using the 2-d gradient wind equations. Note that the resolution horizontal of the AMSU instrument results in a smooth temperature field and an unrealistically low tangential wind speeds. These images are useful in determining the thermal structure of the tropical cyclone
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Quoting iceman55:
wow blog slow like oldman

maybe this will wake up some
Link
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Quoting iceman55:
wow blog slow like oldman

Hey, I'm 48, stop picking on us ol' folk!! Ha, ha, ha :0)!!!
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Well, my geography is failing me, because Isla Mujeres is the one up by Cancun... I'm thinking of the little barrier islands northeast of Chetumal Bay instead :o(...
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Ah, Avila is working Friday night....

Kinda sad this is the most interesting thing abt the TWO... lol



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Quoting Dakster:
Quote from NHC: "THIS...COMBINED WITH A TONGUE OF
COOLER SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK"

Where is this "tongue" of cooler sea surface temperatures?

Kind of an odd statement... But I will work with it.


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438. IKE
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT FRI SEP 25 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON NEWLY FORMED
TROPICAL DEPRESSION EIGHT LOCATED IN THE FAR EASTERN ATLANTIC ABOUT
505 MILES WEST OF THE CAPE VERDE ISLANDS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

PUBLIC ADVISORIES ON TROPICAL DEPRESSION EIGHT ARE ISSUED UNDER WMO
HEADER WTNT33 KNHC AND UNDER AWIPS HEADER MIATCPAT3.
FORECAST/ADVISORIES ARE ISSUED UNDER WMO HEADER WTNT23 KNHC AND
UNDER AWIPS HEADER MIATCMAT3.

$$
FORECASTER AVILA


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Quoting islagal:
No...off the Yucatan. What i wouldn't do for 1 day of snow! i'd be prepared, but what a disaster it would be!
OK, this is between Belize border and Cozumel, then? I always get these two groups of islands confused....

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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.


Imagine being from the Gulf Coast and your first duty station being Minot ND.
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[blockquote]Long term....long term (sunday night through thursday)...12z European model (ecmwf)
and 00z GFS in reasonable agreement for next week. Broad trough is
forecast to build over the eastern Continental U.S. Early in the week pushing a
weak frontal boundary through the forecast area late Sunday...and a
reinforcing front by Tuesday. The initial passage will mainly result
in a drier airmass overspreading the area. Without any cold air advection and full
sunshine...Monday likely to be warmer than Sunday. The secondary
passage is expected to pack a bit more punch allowing for slightly
cooler air to push into the region for the middle of the week. May
even see lows dip into the upper 50s by Wednesday/Thursday mornings. Overall...
next week should be dry with northwest flow aloft.[/blockquote]

What a contrast October will be in The Sunshine State! Looks like the dry season will be inaugurated with our first taste of fall mid-next week!

Bring out the shampain! This causes for a celebration!
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Quoting BahaHurican:
Hola, Isla. U are in the SW Caribbean, right? Columbian islands?

And speaking of winter, with the Bahamas lying athwart the Tropic of Cancer, (passes about 10 miles south of my grannie's house, actually lol) half of the islands are technically subtropical..... lol. In the winter, we can get night temps into the 50s, though I think the record low in the NW Bahamas is in the 40s somewhere. There is also a "report" - unsubstantiated by wx officials - of snow in Grand Bahama during the record 1977 cold season.....
Just looked it up. Isla Mujeres, Mexico
Member Since: October 9, 2008 Posts: 0 Comments: 8268
[blockquote]Long term....long term (sunday night through thursday)...12z European model (ecmwf)
and 00z GFS in reasonable agreement for next week. Broad trough is
forecast to build over the eastern Continental U.S. Early in the week pushing a
weak frontal boundary through the forecast area late Sunday...and a
reinforcing front by Tuesday. The initial passage will mainly result
in a drier airmass overspreading the area. Without any cold air advection and full
sunshine...Monday likely to be warmer than Sunday. The secondary
passage is expected to pack a bit more punch allowing for slightly
cooler air to push into the region for the middle of the week. May
even see lows dip into the upper 50s by Wednesday/Thursday mornings. Overall...
next week should be dry with northwest flow aloft.[/blockquote]

What a contrast October will be in The Sunshine State! Looks like the dry season will be inaugurated with our first taste of fall mid-next week!

Bring out the shampain! This causes for a celebration!
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mkmand - I am happy you were bored this season. I hope you bored for many more.
Member Since: March 10, 2006 Posts: 0 Comments: 10034
No...off the Yucatan. What i wouldn't do for 1 day of snow! i'd be prepared, but what a disaster it would be!
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Sigh! This Hurricane season has been a bore!!!
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Iceman - what is that?
Member Since: March 10, 2006 Posts: 0 Comments: 10034
Quote from NHC: "THIS...COMBINED WITH A TONGUE OF
COOLER SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK"

Where is this "tongue" of cooler sea surface temperatures?

Kind of an odd statement... But I will work with it.
Member Since: March 10, 2006 Posts: 0 Comments: 10034
How does a newbie identify a "wave" on a map or satellite (other than waiting for a pro met to post a pic)? Does a wave always have convection associated with it and what is the best type of map/satellite to use to identify new waves/about to be waves?
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Quoting islagal:
i'm looking forward to the "winter" here in Isla Mujeres too! Trust me...you feel the difference. The down comforter, Frye boots and jacket comes out in the evening...over tshirts and shorts, of course!
Hola, Isla. U are in the SW Caribbean, right? Columbian islands?

And speaking of winter, with the Bahamas lying athwart the Tropic of Cancer, (passes about 10 miles south of my grannie's house, actually lol) half of the islands are technically subtropical..... lol. In the winter, we can get night temps into the 50s, though I think the record low in the NW Bahamas is in the 40s somewhere. There is also a "report" - unsubstantiated by wx officials - of snow in Grand Bahama during the record 1977 cold season.....
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i'm looking forward to the "winter" here in Isla Mujeres too! Trust me...you feel the difference. The down comforter, Frye boots and jacket comes out in the evening...over tshirts and shorts, of course!
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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.
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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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