African tropical wave 99L slowly organizing

By: Dr. Jeff Masters , 1:26 PM GMT on July 31, 2012

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A tropical wave (Invest 99L) near 9°N 41°W, halfway between the Lesser Antilles Islands and the coast of Africa, has the potential to develop into a tropical depression later this week as it moves westward at 10 - 15 mph. Visible satellite loops show that the disturbance now has a moderate amount of poorly-organized heavy thunderstorms that continue to slowly increase in intensity and areal coverage. There is no surface circulation, but some counter-clockwise rotation of the large-scale cloud pattern is evident. Water vapor satellite loops show that 99L has a reasonably moist environment. The latest Saharan air layer analysis shows that the dry air from the Sahara lies to the north of 99L and is currently not affecting the storm. WInd shear over the disturbance is a light 5 - 10 knots, and ocean temperatures are 28°C, (82°F) which is well above the 26.5°C (80°F) threshold typically needed to allow formation of a tropical depression.


Figure 1. Morning satellite image of Invest 99L.

Forecast for 99L
Wind shear is expected to remain light through Friday, and ocean temperatures will remain near 28°C, according to the 8 am EDT run of the SHIPS model. However, a band of high wind shear of 20 - 40 knots associated with the subtropical jet stream lies just to the north of 99L, and it would not be a surprise to see 99L experience some higher shear conditions than are currently forecast. The farther north 99L gets, the higher the shear it will experience, and the SHIPS model is predicting shear in the moderate range, 10 - 20 knots, for Saturday - Sunday, as the storm works its way to 15°N. The disturbance is at 9°N, which is close enough to the Equator that the storm will have some difficultly getting spinning. Most of the models are showing some slow development of 99L. There are some major differences in the predicted forward speed of 99L, with the ECMWF and UKMET models predicting the storm will reach the Lesser Antilles on Friday, and the GFS predicting a later arrival, on Saturday. At 8 am Tuesday, NHC gave 99L a 20% chance of developing into a tropical depression by Thursday morning. I expect the storm will begin having trouble with tendrils of dry air reaching down from the north at times this week, but give 99L a 50% chance of eventually developing into Tropical Storm Ernesto sometime in the next ten days. Residents and visitors to the Lesser Antilles Islands should anticipate heavy rains and strong winds from 99L beginning to affect the islands as early as Friday morning. The long-range fate of 99L next week is uncertain. A track west to west-northwest through the Caribbean, or to the northwest towards the U.S. East Coast are both possible. The storm is less likely to survive if it heads northwest towards the U.S.

Extreme heat in the Central U.S.
The withering heat in America's heartland continued on Monday, with high temperatures of 112° recorded in Winfield, Kansas and Searcy, Arkansas. Little Rock, Arkansas hit 111°, their 3rd hottest temperature ever record, behind the all time record of 114° set just last year on August 3, and the 112° reading of 7/31/1986. Wichita and Coffeyville in Kansas both hit 111° Monday, and in Oklahoma, Enid, Tulsa Jones Airport, and Chandler all topped out at 111°. Carr Creek, Missouri hit 110°, the hottest temperature measured in the state so far this year. Highs temperatures Tuesday and Wednesday in this region could reach 110° again, as the most extreme heat this week will stay focused over Oklahoma and surrounding states.

Jeff Masters

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Quoting ncstorm:


I am not a he..I am a she..I have told this blog this many times and you guys keep calling me dude when addressing me..do I type in "male"
For 28 days a month you do.
I was wondering about those other 3 days.
.
.
.
j/k
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Quoting TropicalAnalystwx13:

Sorry. I forgot.
..dudette?
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Quoting ncstorm:


I am not a he..I am a she..I have told this blog this many times and you guys keep calling me dude when addressing me..do I type in "male"
oh my I thought you were a boy sorry for the confusion.
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Quoting TropicalAnalystwx13:


Too slow. :-p
Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting GTcooliebai:
The NHC broke out with some new crayons:



As I said, people shouldnt sleep on the first wave..
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Quoting GTcooliebai:
And to add if a trough is swinging down on that western periphery of the high pressure it is capable of turning the storm to the Northeast.
..............but..the HIGH would block it from coming INTO the gulf unless the storm was strong enough to push it aside which i doubt it will be
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The NHC broke out with some new crayons:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting ncstorm:


I am not a he..I am a she..I have told this blog this many times and you guys keep calling me dude when addressing me..do I type in "male"

Sorry. I forgot.
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000
ABNT20 KNHC 311732
TWOAT

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT TUE JUL 31 2012

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

A TROPICAL WAVE WITH AN EMBEDDED AREA OF LOW PRESSURE IS LOCATED
NEARLY MIDWAY BETWEEN AFRICA AND THE LESSER ANTILLES. SHOWERS AND
THUNDERSTORMS ASSOCIATED WITH THIS DISTURBANCE HAVE BECOME SLIGHTLY
BETTER ORGANIZED SINCE YESTERDAY. ENVIRONMENTAL CONDITIONS ARE
CONDUCIVE FOR SOME GRADUAL DEVELOPMENT OF THIS LOW OVER THE NEXT
FEW DAYS. THIS SYSTEM HAS A MEDIUM CHANCE...30 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES
WESTWARD AT AROUND 15 MPH.

A WESTWARD-MOVING TROPICAL WAVE OVER THE CENTRAL CARIBBEAN IS
PRODUCING WIDESPREAD CLOUDINESS AND THUNDERSTORMS FROM HISPANIOLA
EASTWARD FOR SEVERAL HUNDRED MILES. UPPER-LEVEL WINDS ARE NOT
FAVORABLE FOR DEVELOPMENT...AND THIS SYSTEM HAS A LOW CHANCE...NEAR
0 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48
HOURS. HEAVY RAINS AND GUSTY WINDS ASSOCIATED WITH THIS WAVE WILL
SPREAD OVER HISPANIOLA...EASTERN CUBA...AND THE SOUTHEASTERN
BAHAMAS DURING THE NEXT DAY OR TWO.

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

$$
FORECASTER KIMBERLAIN
Member Since: March 16, 2012 Posts: 127 Comments: 7927
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30% for 99L, PR wave mentioned with 0%.
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Member Since: July 15, 2006 Posts: 17 Comments: 10159
506. JLPR2
99L seems disrupted in the west side by the flow of the ITCZ.
Member Since: September 4, 2007 Posts: 7 Comments: 8499
Quoting TropicalAnalystwx13:

Yours is 00Z, his is 12Z.


I am not a he..I am a she..I have told this blog this many times and you guys keep calling me dude when addressing me..do I type in "male"
Member Since: Posts: Comments:
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT TUE JUL 31 2012

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

A TROPICAL WAVE WITH AN EMBEDDED AREA OF LOW PRESSURE IS LOCATED
NEARLY MIDWAY BETWEEN AFRICA AND THE LESSER ANTILLES. SHOWERS AND
THUNDERSTORMS ASSOCIATED WITH THIS DISTURBANCE HAVE BECOME SLIGHTLY
BETTER ORGANIZED SINCE YESTERDAY. ENVIRONMENTAL CONDITIONS ARE
CONDUCIVE FOR SOME GRADUAL DEVELOPMENT OF THIS LOW OVER THE NEXT
FEW DAYS. THIS SYSTEM HAS A MEDIUM CHANCE...30 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES
WESTWARD AT AROUND 15 MPH.

A WESTWARD-MOVING TROPICAL WAVE OVER THE CENTRAL CARIBBEAN IS
PRODUCING WIDESPREAD CLOUDINESS AND THUNDERSTORMS FROM HISPANIOLA
EASTWARD FOR SEVERAL HUNDRED MILES. UPPER-LEVEL WINDS ARE NOT
FAVORABLE FOR DEVELOPMENT...AND THIS SYSTEM HAS A LOW CHANCE...
0 PERCENT
...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48
HOURS. HEAVY RAINS AND GUSTY WINDS ASSOCIATED WITH THIS WAVE WILL
SPREAD OVER HISPANIOLA...EASTERN CUBA...AND THE SOUTHEASTERN
BAHAMAS DURING THE NEXT DAY OR TWO.

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

$$
FORECASTER KIMBERLAIN
Member Since: Posts: Comments:
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502. JLPR2
Quoting MississippiWx:




And no, a closed isobar does not represent a closed low.


Hmm.. You're right!

OSCAT has a clean pass over 99L, better structure, but not a closed low yet.

Member Since: September 4, 2007 Posts: 7 Comments: 8499
Quoting HurricaneFetish:


Yes it does, Drew.


It really doesn't, but you can believe what you want.
Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting TideWaterWeather:


Ummm... tropical systems will tend to rotate around the high (clockwise).. in this case it would be rotating around the western edge of the high so the direction would turn NW/N. That could put in in the southern GOM. IF* it were to make it all the way across the Caribbean.
And to add if a trough is swinging down on that western periphery of the high pressure it is capable of turning the storm to the Northeast.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting TideWaterWeather:


Ummm... tropical systems will tend to rotate around the high (clockwise).. in this case it would be rotating around the western edge of the high so the direction would turn NW/N. That could put in in the southern GOM. IF* it were to make it all the way across the Caribbean.
..yes but the HIGH is blocking the way in..and what would PULL the whatever it becomes..northward instead of following the other waves west
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The U.S. left little doubt who had the best women's gymnasts in the world, easily winning the team gold medal.
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Quoting reedzone:


Two things...

1. Wind shear is 5-10 knots, conditions are currently favorable under that wave..

2. Don't mention politics on here.




I'm not a expert but is clearly that wind shear is afecting the wave in the carribean in the north part and in the west.

And about the politics yes, sorry my,
Member Since: June 20, 2012 Posts: 0 Comments: 2150
Here is the 500mb comparison of the Euro/GFS again. I showed this yesterday and the Euro is basically the same. However, the GFS has a much weaker trough than it had on yesterday's comparison over the Eastern Seaboard. You can still see a slight dip in the jet stream over Mid-Atlantic states, but with 99L staying so far to the south it would most likely have to be a pretty strong storm to feel the influence of a trough that weak. Still 8-10 days out of course and plenty of time for change.

Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting TropicalAnalystwx13:

That's because conditions are always favorable, or forecast to become, according to him.

But yes, things have changed since yesterday. It looks like this system has more of a chance to survive in the Carribbean than was originally thought yesterday.


You seem to have a problem with him..he has been right on several occasions this season..

yesterday, today, and tomorrow..nothing is set in stone except Grothar's Birth Certificate
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Quoting TropicalAnalystwx13:

That's because conditions are always favorable, or forecast to become, according to him.

But yes, things have changed since yesterday. It looks like this system has more of a chance to survive in the Carribbean than was originally thought yesterday.
yeah...antoher think is that people confuse shear with trade winds a lot.
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Quoting LargoFl:
..i have a question..WHAT are you guys looking at..that would PULL 99L northward?..the bermuda high is there..there is a big high in the gulf..what makes you or the models for that matter...think this blob is going into the gulf?..a huge right hand turn..like a magnet for storms was up there....no..there isnt any


Ummm... tropical systems will tend to rotate around the high (clockwise).. in this case it would be rotating around the western edge of the high so the direction would turn NW/N. That could put it in the southern GOM. IF* it were to make it all the way across the Caribbean. Still a ton of if's in all this.. so we shall just wait and see what happens
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Good Afternoon everyone
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Quoting GTcooliebai:
Ok what gives, why is my model run different from yours? I got mine direct from the Canadian Model website.

Yours is 00Z, the one she posted is 12Z.
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Quoting allancalderini:
I remember that wunderkidcayman say that conditions were favorable in the caribbean better than north of the islands looks that he was right.

That's because conditions are always favorable in the Caribbean, or forecast to become favorable, according to him.

But yes, things have changed since yesterday. It looks like this system has more of a chance to survive in the Carribbean than was originally thought yesterday.
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Quoting ncstorm:


I dont know?..here is the link where I get the Canadian model..it takes a while though for the precip map to update

Link
Ok yours is the updated one, because mine looked familiar like yesterdays 12z run. Thanks I'll bookmark this one. Still has the northward bias in track.

Member Since: August 31, 2009 Posts: 0 Comments: 5628
485. JLPR2
Quoting Pocamocca:

Afternoon, portapete.

And no, 99L is an open low. Not closed.


...
Member Since: September 4, 2007 Posts: 7 Comments: 8499
Why is it coming from the E???
Quoting ncstorm:


I dont know?..here is the link where I get the Canadian model..it takes a while though for the precip map to update

Link
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Quoting GTcooliebai:
Ok what gives, why is my model run different from yours? I got mine direct from the Canadian Model website.


I dont know?..here is the link where I get the Canadian model..it takes a while though for the precip map to update

Link
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Quoting MississippiWx:


Don't believe yours is updated yet.
What?! That's ridiculous, I got that straight from Environmental Canada, you would think it would update there first.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
I remember that wunderkidcayman say that conditions were favorable in the caribbean better than north of the islands looks that he was right.
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Quoting RussianWinter:



Oh man, Imagine tracks like this and a Florida-bound could really make things ugly this season (Or any other storm passing through the Yucatan strait).

It's like Herbert Box 2.0, only bigger and badder.




..i have a question..WHAT are you guys looking at..that would PULL 99L northward?..the bermuda high is there..there is a big high in the gulf..what makes you or the models for that matter...think this blob is going into the gulf?..a huge right hand turn..like a magnet for storms was up there....no..there isnt any
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Anyone notice that Dr M said 99L had less of a chance to survive if it goes North of the Caribbean, which is opposite of what most of us were saying the last few days?
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Quoting GTcooliebai:
Ok what gives, why is my model run different from yours? I got mine direct from the Canadian Model website.


Don't believe yours is updated yet.
Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting HurricaneFetish:



1008mb is closed, not open.

Note the closed circle around the low.

Therefore, it shows it as a depression.


Welcome back, Janiel.

And no, a closed isobar does not represent a closed low.
Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting ncstorm:
12z CMC..180 hours

1008mb open low
Ok what gives, why is my model run different from yours? I got mine direct from the Canadian Model website.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
471. etxwx
Standing up to severe weather
July 28, 2012 CBS News: With tougher building standards, severe weather doesn't have to be so destructive anymore.
This is a brief video report from CBS news on building damage during severe storms. About 40 seconds in, it shows a strip mall style building model subjected to Cat 2 winds in a research lab . Video Link
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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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