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 TropicalAnalystwx13:

Huh?



Do you have graphics that support less Caribbean Trade winds?
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Quoting TropicalAnalystwx13:

Huh?



However, it will still be under that small upper anticyclone...this is even forecast by SHIPS, shortly thereafter, conditions improve. Temporary setback...It shouldn't destroy the system.
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Quoting GTcooliebai:
"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." I'm assuming that is because of the TUTT? And has the trade winds weakened somewhat?

Weird how forecasts can change in a matter of a day.
And yes TUTT would affect.
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The GFS is actually stronger with the 12z than the 6z about the Alabama storm exiting off the NC coast-30 hours

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72 HR:


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Quoting StormTracker2K:


Yeah well see about that! Caribbean is not as hostile as one would think. I will laugh if you poof 99L and it turns out to be an Ivan.



It would be quite ironic if I where to poof something when I've been ranting about patience with these systems for years.

Please calm down.
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Carl Parker said this is getting close to tropical depression status. And it would be if it weren't connected to the Intertropical Convergence Zone still. Once we see it detach, we should see classification.
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Quoting StormTracker2K:
GFS 60hrs

slow mover
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Quoting islander101010:
lucky.the.eye.didnt.go.over.miami
The eye was only 8 miles wide but caused enough destruction in its path. I wouldn't say it is lucky just because downtown Miami didn't get the brunt of it. Virtually anything south of Kendall got destroyed.
Member Since: May 16, 2010 Posts: 0 Comments: 1472
GFS still has 850 winds at 25 knots in the Caribbean ahead of 99L. Good luck trying to get an open wave to close off with that.

Like I said, best chance is for a sleeper wave to stroll though the Caribbean and possibly do something in the GOM.



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Quoting reedzone:


Completely different pattern from the last 3-4 years.

Hello Reed. How are ya?
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Quoting GeorgiaStormz:

Edit Failed!
Who turned the hose on Alabama?:


Whoa, how'd i do this?


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66 HR: Two invests.



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GFS 60hrs

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"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." I'm assuming that is because of the TUTT? And has the trade winds weakened somewhat?
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Quoting CybrTeddy:


Because this is what the GFS is predicting for shear.

Huh?

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Quoting reedzone:


Completely different pattern from the last 3-4 years.


Hey Reed...how ya been?
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Quoting robert88:


Yes indeed. I'm also a little worried for the islands and US with that strong Bermuda high setup. That could be a dangerous recipe.


Completely different pattern from the last 3-4 years.
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HR 60. 99L is really south.

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Quoting StormTracker2K:


Yeah well see about that! Caribbean is not as hostile as one would think. I will laugh if you poof 99L and it turns out to be an Ivan.



These folks must be dreaming up these "fierce" E. Caribbean surface winds.
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August Averages
(Not for Navigational Purposes)
20° 0.0´N 73° 8.4´W
SST: 29.2°C (84.5°F)
Wind: 90.9° (E) at 11.6 knots
Current: 0.8 knots - Heading 301.0°T
Air Temp: 28.0°C (82.5°F)
Precip: 7.27"
Water
Clarity: 35 m (116 ft)
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Quoting CybrTeddy:


I always read back on the blog when I log.

There's no chance of it surviving in the Caribbean either.


Yeah well see about that! Caribbean is not as hostile as one would think. I will laugh if you poof 99L and it turns out to be an Ivan.

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Quoting TropicalAnalystwx13:

The end of August is going to be very active.



Yes indeed. I'm also a little worried for the islands and US with that strong Bermuda high setup. That could be a dangerous recipe.
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TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT TUE JUL 31 2012

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

A WEAK AREA OF LOW PRESSURE ASSOCIATED WITH A TROPICAL WAVE LOCATED
ABOUT 1150 MILES WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS CONTINUES
TO PRODUCE DISORGANIZED SHOWER AND THUNDERSTORM ACTIVITY.
ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE FOR SOME GRADUAL
DEVELOPMENT OF THIS LOW OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
LOW CHANCE...20 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS AS IT MOVES WESTWARD AT 10 TO 15 MPH.

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


I always read back on the blog when I log.

There's no chance of it surviving in the Caribbean either.


????
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Quoting TropicalAnalystwx13:

I'm going to have to disagree. If a tropical wave with a well-defined vorticity maximum can stay well-defined to the central Caribbean with no signs of weakening, why can't a stronger and more well-defined tropical cyclone? It doesn't make any sense.


Because this is what the GFS is predicting for shear.
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Good morning, y'all...

Watching the GFS right now. At 48 HR, cyclone is 1011 mb.
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Quoting TropicalAnalystwx13:


The only way that i see 99L recurve is if he develops in strong Storm or Cat.1 about 50 miles away of Windward islands, and push the ridge, something like CMC is predicting
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More of the colorado 2nd highest on record tornado:

Member Since: February 11, 2012 Posts: 0 Comments: 9726
India hit by second, even larger power outage

India suffered its second huge, crippling power failure in two days Tuesday, depriving as much as half of the vast and populous country, or up to 600 million people, of electricity and disrupting transport networks.

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Quoting Pocamocca:

Yep.


You guys make me laugh.
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GFS 42hrs.

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Quoting CybrTeddy:


I always read back on the blog when I log.

There's no chance of it surviving in the Caribbean either.

I'm going to have to disagree. If a tropical wave with a well-defined vorticity maximum can stay well-defined to the central Caribbean with no signs of weakening, why can't a stronger and more well-defined tropical cyclone? It doesn't make any sense.

Just look at the satellite loops of the Caribbean for yourself. They're [the trade winds] not strong at all.
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Storm Relative 16km Microwave-Based Total Precipitable Water Imagery

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Storm Relative 1km Geostationary Visible Imagery

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Quoting stormchaser19:


Still in 20%
I think NHC will wait maybe 3 advisories to declare DEPRESION

c)TD tomorrow and maybe d)
Tomorrow.
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Quoting TropicalAnalystwx13:

Read back on the blog a bit.

Oh, and Dr. Masters,

"The storm is less likely to survive if it heads northwest towards the U.S."


I always read back on the blog when I log.

There's no chance of it surviving in the Caribbean either.
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Quoting robert88:


They might not be quite as strong as a week or 2 ago...but they are there. You can see the trade winds blowing those clouds in the S Caribbean W to E. There is enough to inhibit development. Looking at satellite you can still see some dry air in that region as well. The bottom line it's just too stable in the W Atlantic for things to really take off. I believe we are at the beginning stages for a very busy August. The MJO is really going to kick off the fireworks in a couple of weeks imo.

The end of August is going to be very active.

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Who turned the hose on Alabama?:


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Quoting Pocamocca:
TD a day after tomorrow!
Last week there was a survey as to when the next storm would develop (officially)...I had predicted Aug 1st @ 4:45pm...but it will probably be after that.
Member Since: May 16, 2010 Posts: 0 Comments: 1472

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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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