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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Good Morning From America's Left Coast at 5:25 PDT
Member Since: September 18, 2010 Posts: 0 Comments: 5222
Quoting TropicalAnalystwx13:
If you ever needed any more proof that the Caribbean is not unfavorable:

hey cody. now im noticing something different on the model runs. instead of weakining 99L once it enters the carribean, it instead should maintain itself and once it gets west of jamaica should start to stregthen. anywhere from northern mexico to the florida panhandle should watch out
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Quoting wunderkidcayman:

dude do you know how long I have been saying that

You say it all the time, that's nothing new. ;)
Member Since: July 6, 2010 Posts: 113 Comments: 32056
2118. pottery
Quoting washingtonian115:
Hey Pottery and Gro.I'm still confused.Some people say if it goes north of the islands it will be killed or organize.If it goes into the caribbean it will be killed or organized.Lol XD.Hope your prepared Pottery.

Yep.
It's good to know that things are so clear......

And have no fear, I am well prepared for everything except wind and rain.
We don't do wind too well here.
And rain is fine once it's not heavy.
In fact, come to think of it, it would be nice if this #99 just went away right now.
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2117. Chiggy
Quoting Chiggy:


These are all two days old - 07/30.


The latest run I can find on the 06Z GFS is at 174hrs. Which shows a TS approaching channel between Cuba and Yucatan!


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2116. LargoFl
Quoting washingtonian115:
Oh well that's just great....Well eh you Gulf coast residents watching this to?.
..yes watching it but thats about it..just watching, I doubt this is OUR storm in the gulf, the Islands really need to watch it though
Member Since: August 6, 2011 Posts: 4 Comments: 38509
000
ABNT30 KNHC 011157
TWSAT

MONTHLY TROPICAL WEATHER SUMMARY
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT WED AUG 1 2012

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

NO TROPICAL CYCLONES FORMED IN THE ATLANTIC BASIN DURING THE MONTH
OF JULY. BASED ON A 30-YEAR AVERAGE FROM 1981 TO 2010...ABOUT ONE
NAMED STORM FORMS IN THE BASIN IN JULY. HOWEVER...IT IS NOT
UNUSUAL TO HAVE NO TROPICAL STORMS DEVELOP DURING JULY.

IN TERMS OF ACCUMULATED CYCLONE ENERGY...WHICH MEASURES THE COMBINED
STRENGTH AND DURATION OF TROPICAL STORMS AND HURRICANES...TROPICAL
CYCLONE ACTIVITY SO FAR THIS YEAR IS A LITTLE ABOVE THE 1981-2010
AVERAGE IN THE ATLANTIC BASIN.

REPORTS ON INDIVIDUAL CYCLONES...WHEN COMPLETED...ARE AT THE WEB
SITE OF THE NATIONAL HURRICANE CENTER...USE LOWER-CASE LETTERS...
WWW.HURRICANES.GOV/2012ATLAN.SHTML

SUMMARY TABLE

NAME DATES MAX WIND (MPH)
------------------------------------------------- --
TS ALBERTO 19-22 MAY 60
TS BERYL 26-30 MAY 70
H CHRIS 19-22 JUN 75
TS DEBBY 23-27 JUN 60
------------------------------------------------- --

$$
HURRICANE SPECIALIST UNIT
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Quoting TropicalAnalystwx13:
If you ever needed any more proof that the Caribbean is not unfavorable:


dude do you know how long I have been saying that
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2065 islander101010: butterfly island is a magnet

Less Guadeloupe being a magnet and more Barbados being a springboard.
When the leading fringes of a TropicalCyclone hits Barbados -- if they are already north enough -- they compress into a denser mass, leading to a sort of backpressure toward the TC.
And the TC in turn climbs that fixed-to-Barbados backpressure/mass counterclockwise-northward in a pseudo-Fujiwhara manner.
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2112. Grothar
Quoting pottery:


Hmmmmmmm.


I always enjoy your analyses of these systems.
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2111. LargoFl
.........................................still a long ways off and doesnt look all that impressive and remember it is NOT..a tropical storm YET..but we keep watching it...we shall see maybe tomorrow a storm developed..if not then ..hmmm maybe just a weak tropical storm?
Member Since: August 6, 2011 Posts: 4 Comments: 38509
Quoting TropicalAnalystwx13:
If you ever needed any more proof that the Caribbean is not unfavorable:

Oh well that's just great....Well eh you Gulf coast residents watching this to?.
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2109. Grothar
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2108. ncstorm
Quoting Chiggy:


These are all two days old - 07/30.


Ahh..thanks..didnt refresh
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Quoting pottery:

True!
Going to be a wet party for you guys this weekend.
Have fun though !
Should be more fun in the rain. Hope you did not have any plans for weekend?
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Sun has just come up, but trade winds do not look strong.
Member Since: July 6, 2010 Posts: 113 Comments: 32056
Hey Pottery and Gro.I'm still confused.Some people say if it goes north of the islands it will be killed or organize.If it goes into the caribbean it will be killed or organized.Lol XD.Hope your prepared Pottery.
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2104. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 38509
Quoting TropicalAnalystwx13:
If you ever needed any more proof that the Caribbean is not unfavorable:

Oh... that's gonna be fun.
Member Since: August 1, 2011 Posts: 28 Comments: 8009
2102. Chiggy
Quoting ncstorm:
I cant get frames on Allan's site but here is the NCEP Model guidance for the 06z GFS

192 hours


204 hours






These are all two days old - 07/30.
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Wow Cat 2!!
Quoting TropicalAnalystwx13:
If you ever needed any more proof that the Caribbean is not unfavorable:

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2100. pottery
Quoting barbados246:
Good morning Pottery whats life without a 'lil" fun

True!
Going to be a wet party for you guys this weekend.
Have fun though !
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If you ever needed any more proof that the Caribbean is not unfavorable:

Member Since: July 6, 2010 Posts: 113 Comments: 32056
2098. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 38509
Quoting pottery:

Well, this looks like fun.... !

Not sure I want any fun though...

Good Morning all.
Good morning Pottery whats life without a 'lil" fun
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Quoting GeorgiaStormz:
So to PASCH conditions are favorable but to STEWART they are only marginal

Stewart said at least marginally conducive.
Member Since: July 6, 2010 Posts: 113 Comments: 32056
It going WNW???
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2094. ncstorm
I cant get frames on Allan's site but here is the NCEP Model guidance for the 06z GFS

.
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So to PASCH conditions are favorable but to STEWART they are only marginal
Member Since: February 11, 2012 Posts: 0 Comments: 9727
2092. pottery
Quoting Grothar:
This looks like a good one.


Lucky you !
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2091. LargoFl
Quoting SFLWeatherman:
Pileus clouds, created by a layer of ice crystals and thunderstorms, turn heads yesterday
..what an amazing sight to see that, nice one
Member Since: August 6, 2011 Posts: 4 Comments: 38509
2090. Grothar
Quoting washingtonian115:
There you are.Hey Pottery and good morning to you WU.


Hey Wash!
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2089. pottery
Quoting washingtonian115:
There you are.Hey Pottery and good morning to you WU.

'Morning to you.
This one looks a little "Ominizing" down the road, I think.
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10N now!!!!:)
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2087. Guysgal
10% of WORLD'S population without power! Link
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2086. Grothar
This looks like a good one.

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It's August!!


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Quoting pottery:

Well, this looks like fun.... !

Not sure I want any fun though...

Good Morning all.
There you are.Hey Pottery and good morning to you WU.
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!!!
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2082. Grothar
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Quoting Neapolitan:
Big Red:

99L
actually, its a satellite pic...I see no red...lol
Member Since: May 16, 2010 Posts: 0 Comments: 1472
2080. Chiggy


00Z HWRF at 126 hrs
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2079. SLU
CARIBBEAN SEA AND TROPICAL ATLC W OF 55W...
HEALTHY TROPICAL WAVE ALONG 73W PRODUCE FRESH E BREEZE WITHIN
240 NM OF AXIS. WAVE REACH WESTERN CARIBBEAN THU AND FRI BEFORE
MOVING W OF AREA SAT. SECOND AND STRONGER TROPICAL WAVE AND
ASSOCIATED SURFACE LOW PRES...POSSIBLE TROPICAL CYCLONE...
CURRENTLY NEAR 10N44W MOVE W THROUGH FORECAST PERIOD AND REACH
TROPICAL N ATLC WATERS FRI AND FAR E CARIBBEAN WATERS LATE SAT
AND SUN. WIND AND SEAS EXPECTED TO INCREASE SIGNIFICANTLY THEN
ALONG WITH ASSOCIATED DEEP CONVECTION.
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Quoting SFLWeatherman:
Pileus clouds, created by a layer of ice crystals and thunderstorms, turn heads yesterday

Nice!
Member Since: May 16, 2010 Posts: 0 Comments: 1472
2077. pottery
Quoting SLU:
.ATLC LOW PRES AT 10N44W 1009 MB MOVING W AT 17 KT. WITHIN 240
NM NE SEMICIRCLE WINDS 20 TO 25 KT. SEAS TO 10 FT. WINDS AND
SEAS HIGHER NEAR NUMEROUS TSTMS WITHIN 180 NM W SEMICIRCLE.
.24 HOUR FORECAST LOW PRES...POSSIBLE TROPICAL CYCLONE...NEAR
11N51W 1009 MB. WITHIN 240 NM NE AND 120 NM SW SEMICIRCLES
WINDS 20 TO 30 KT. SEAS TO 12 FT.
.48 HOUR FORECAST LOW PRES...POSSIBLE TROPICAL CYCLONE...NEAR
12N58W 1008 MB.
WITHIN 270 NM NE AND 120 NM SW SEMICIRCLES
WINDS 20 TO 30 KT. SEAS TO 15 FT NE SEMICIRCLE AND TO 10 FT SW
SEMICIRCLE.


Hmmmmmmm.
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Big Red:

99L
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Still in agreement with HWFI:

Member Since: July 6, 2010 Posts: 113 Comments: 32056
2074. SLU
Quoting pottery:

Well, this looks like fun.... !

Not sure I want any fun though...

Good Morning all.


morning pottery

rain on the horizon!
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2073. Chiggy


06Z GFS at 174hrs - seems reasonable. This run doesn't dissipate the system - rather slowly intensifies it!
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2072. Grothar
As you can see from this, the system has moved quite a bit more WNW than a due west course since its earlier position.

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2071. SLU
.ATLC LOW PRES AT 10N44W 1009 MB MOVING W AT 17 KT. WITHIN 240
NM NE SEMICIRCLE WINDS 20 TO 25 KT. SEAS TO 10 FT. WINDS AND
SEAS HIGHER NEAR NUMEROUS TSTMS WITHIN 180 NM W SEMICIRCLE.
.24 HOUR FORECAST LOW PRES...POSSIBLE TROPICAL CYCLONE...NEAR
11N51W 1009 MB. WITHIN 240 NM NE AND 120 NM SW SEMICIRCLES
WINDS 20 TO 30 KT. SEAS TO 12 FT.
.48 HOUR FORECAST LOW PRES...POSSIBLE TROPICAL CYCLONE...NEAR
12N58W 1008 MB. WITHIN 270 NM NE AND 120 NM SW SEMICIRCLES
WINDS 20 TO 30 KT. SEAS TO 15 FT NE SEMICIRCLE AND TO 10 FT SW
SEMICIRCLE.
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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.