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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How strong will 99L peak as before reaching the Leeward Islands?

A. Invest
B. Tropical Depression (<35 knots)
C. Tropical Storm (35-45 knots)
D. Severe Tropical Storm (50-60 knots)
E. Hurricane (>65 knots)

Going with D.
Member Since: July 6, 2010 Posts: 112 Comments: 31314
1319. ncstorm
Quoting Bluestorm5:
I'll like my crow with ketchup, please... 50%? Wow...


Dont worry..it was Buffet night here at WU, you wont be eating alone..
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Quoting JLPR2:


I'm surprised, wasn't expecting 50%, more like 40%.


Pretty decent turning, there is not much to stop it from becoming a depression at the moment.
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The National Weather Service in State College PA has issued a

* Severe Thunderstorm Warning for...
northeastern Cumberland County in south central Pennsylvania...
Dauphin County in south central Pennsylvania...
northern Lancaster County in south central Pennsylvania...
Lebanon County in south central Pennsylvania...
east central Perry County in south central Pennsylvania...
southwestern Schuylkill County in central Pennsylvania...
northern York County in south central Pennsylvania...

* until 845 PM EDT

* at 735 PM EDT... National Weather Service Doppler radar indicated a
line of severe thunderstorms. These severe storms extended from
Ellendale Forge to Spry... moving northeast at 25 mph. These storms
are capable of producing damaging winds in excess of 60 mph.

* Locations in the warning include...
Stonybrook and Skyline View...
Elizabethville and DeHart dam...
Penn National raceway and Hershey...
Palmyra and Campbelltown...
lawn and Mount Joy...
Williamstown and Harper Tavern...
Member Since: February 13, 2012 Posts: 11 Comments: 3626
I'll like my crow with ketchup, please... 50%? Wow...
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ENVIRONMENTAL CONDITIONS
ARE AT LEAST MARGINALLY CONDUCIVE FOR SOME GRADUAL DEVELOPMENT OF
THIS DISTURBANCE

not too excited it seems
Member Since: February 11, 2012 Posts: 0 Comments: 9716
ENVIRONMENTAL CONDITIONS ARE AT LEAST MARGINALLY CONDUCIVE FOR SOME GRADUAL DEVELOPMENT OF THIS DISTURBANCE OVER THE NEXT FEW DAYS AS IT MOVES WESTWARD AT 15 TO 20 MPH.
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1312. ncstorm
Dust off the HWRF and GFDL because they will start running them again on 99L..probably the 00z runs..
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Ever notice how some of these systems in the rotation tend to follow cycles? 2006's Ernesto plowed through the Caribbean on a trajectory this one is likely to follow. In 1983, Alicia hit Houston. In 1989, Allison hit the same location.

Interesting, that.
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1308. KEEPEROFTHEGATE (Mod)
x
Member Since: July 15, 2006 Posts: 168 Comments: 53285
cant seem to find a sat image of Hurricane Hugo at cat 5 strength!
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Quoting PensacolaDoug:




You're right! Lets all log off for one week and then come back and see how it's going.

Ok Doug you got me on that one.....
You are on a roll tonight, with "Seymore the Blind Squirrel" and Now telling everybody to log off for a week.... OMG this site would "EXPLODE"...... Just Saying :o)

Taco :o)
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1302. JLPR2
Quoting TropicalAnalystwx13:
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT TUE JUL 31 2012

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



$$
FORECASTER STEWART


I'm surprised, wasn't expecting 50%, more like 40%.
Member Since: September 4, 2007 Posts: 7 Comments: 8482
T.D by late tomorrow morning it seems..IMO.
Member Since: August 14, 2010 Posts: 10 Comments: 16325
This happens every year on here nearing the height of the season.
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TROPICAL WEATHER OUTLOOK

NWS NATIONAL HURRICANE CENTER MIAMI FL

800 PM EDT TUE JUL 31 2012



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



SHOWERS AND THUNDERSTORMS HAVE BECOME A LITTLE MORE CONCENTRATED

NEAR THE CENTER OF A LOW PRESSURE SYSTEM LOCATED ABOUT 1150 MILES

EAST-SOUTHEAST OF THE WINDWARD ISLANDS. ENVIRONMENTAL CONDITIONS

ARE AT LEAST MARGINALLY CONDUCIVE FOR SOME GRADUAL DEVELOPMENT OF

THIS DISTURBANCE OVER THE NEXT FEW DAYS AS IT MOVES WESTWARD AT

15 TO 20 MPH. THIS SYSTEM HAS A MEDIUM CHANCE...50 PERCENT...OF

BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS
Member Since: Posts: Comments:
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT TUE JUL 31 2012

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

SHOWERS AND THUNDERSTORMS HAVE BECOME A LITTLE MORE CONCENTRATED
NEAR THE CENTER OF A LOW PRESSURE SYSTEM LOCATED ABOUT 1150 MILES
EAST-SOUTHEAST OF THE WINDWARD ISLANDS. ENVIRONMENTAL CONDITIONS
ARE AT LEAST MARGINALLY CONDUCIVE FOR SOME GRADUAL DEVELOPMENT OF
THIS DISTURBANCE OVER THE NEXT FEW DAYS AS IT MOVES WESTWARD AT
15 TO 20 MPH. THIS SYSTEM HAS A MEDIUM CHANCE...50 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS

A WESTWARD-MOVING TROPICAL WAVE OVER THE CENTRAL CARIBBEAN SEA IS
PRODUCING WIDESPREAD CLOUDINESS AND THUNDERSTORMS FROM HISPANIOLA
EASTWARD FOR SEVERAL HUNDRED MILES. THERE ARE NO SIGNS OF A SURFACE
CIRCULATION...AND UPPER-LEVEL WINDS ARE NOT FAVORABLE FOR ANY
SIGNIFICANT DEVELOPMENT TO OCCUR. THIS SYSTEM HAS A LOW CHANCE...
NEAR 0 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT
48 HOURS. HOWEVER...LOCALLY HEAVY HEAVY RAINFALL AND GUSTY WINDS
ASSOCIATED WITH THIS WAVE WILL SPREAD ACROSS 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 STEWART
Member Since: July 6, 2010 Posts: 112 Comments: 31314
Quoting taco2me61:

I agree "We All Need To Wait", step back and lets see what's going to happen. I mean my goodness it is over 15 days away and where there may not be much sear right now there will be...
Just Saying :o)

Taco :o)




You're right! Lets all log off for one week and then come back and see how it's going.
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I'll be surprised if it's above 40% for next 48 hours, but I'll give it 60% for 72 hours.
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Quoting robert88:
I can't believe some of these comments. People are already talking hurricane and it hasn't even hit TD status.

I agree "We All Need To Wait", step back and lets see what's going to happen. I mean my goodness it is over 15 days away and where there may not be much sear right now there will be...
Just Saying :o)

Taco :o)
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1294. MahFL
Quoting LargoFl:
................................east coast get ready..up and down the whole coastline in a few


The rain actually missed me in Orange Park.
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1293. etxwx
Heavy rains hit Metro Manila as LPA surfaces near Laoag
August 01, 2012 06:41 AM
Excerpt: MANILA, Philippines - Heavy rains struck parts of Metro Manila and Luzon from Tuesday night to Wednesday morning as a low pressure area (LPA) suddenly developed near Laoag City while typhoon "Gener" (international codename Saola) edges the vicinity of eastern Taiwan. The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) issued a yellow warning signal in Metro Manila prompting more local government units and schools to suspend classes.
PAGASA said that from 5:25 a.m., moderate to heavy rains will hit Camanava (Caloocan, Malabon, Navotas, Valenzuela), Manila, Quezon City, Mandaluyong, San Juan, Makati and Pasig for three hours or until 8 a.m.
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Quoting TropicalAnalystwx13:

Going to have to agree with you there.



Thats what I said yesterday lol.

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Well...Doc's not very impressed with 99l :( It looks pretty good to me....I'm so confused...
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Quoting PensacolaDoug:



Don't be talkin' 'bout my blind squirrel...
His name is "Seymore" FYI.
ROTFLMAO.

"His name is "Seymore"(see more).
Member Since: August 14, 2010 Posts: 10 Comments: 16325
Quoting JLPR2:


Cat 5!

XD




PINHOLE EYE!!!
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Our yellow circle of near 0% has a big blow up this evening!
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Quoting robert88:
Well there is going to be a lot of sad wishcasters out there. :)
You're dissing them because they are saying hurricane but you're downcasting is the same thing. They nor you "KNOW" what will become of 99L but everyone is entitled to their opinion.
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Quoting ncstorm:


is that how your blind squirrel find you:)



Don't be talkin' 'bout my blind squirrel...
His name is "Seymore" FYI.
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Well there is going to be a lot of sad wishcasters out there. :)
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1284. JLPR2
Quoting robert88:
I can't believe some of these comments. People are already talking hurricane and it hasn't even hit TD status.


Cat 5!

XD
Member Since: September 4, 2007 Posts: 7 Comments: 8482
I can't believe some of these comments. People are already talking hurricane and it hasn't even hit TD status.
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Quoting Pocamocca:

Then talk about right time, right place!


big blunder in my eyes, tropicfreak: just explained to me why it looks that way, slaps myself in the face and laughs at myself, hell we all goof up, thing is to laugh about it once no one gets hurt!
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1281. ncstorm
18z GFS Ensemble Spread




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Quoting tropicfreak:


Those are just 2 wind barbs that are close to each other. One is measuring 8 mph while another is measuring 3 mph.


tks , you're right just noticed, laughing at myself!
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not.worried.
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1276. ncstorm
Quoting PensacolaDoug:



Even a blind squirrel finds a nut once in a while.


is that how your blind squirrel find you:)
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Quoting Pocamocca:

That's okay. At least you weren't the one that thinks it'll make it to a cat 4 by the time it get's to the Caribbean. LOL

Look at it that way. ;-)
seen.it.happen.before...slow.mover=rapid.developm ent.could.happen
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Finally. For the first time this year we have not one, but two promising looking AOIs in the Atlantic.
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Quoting Pocamocca:

Uhhhhh Yeah. LOL. Earlier there was an erroneous heat index reading out in Oklahoma at 150 degrees. Sure okay...if the NWS had the thermometer in the back seat of a car sitting in the sun all day.


Remote possibility a waterspout could have went ashore briefly, this has happened where I live before.
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Still No rain showers from the nearby tropical wave,
here in TCI.... I'm starting to think all the rain may stay South of us.
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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.