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 yqt1001:
I've been away for a few days and am tethering so I don't want to use tons of data loading other pages. I see 99L at 50% on NHC and would like some more information on what it may do and how strong it will be in the future.

If you want mine, Will:

Quoting TropicalAnalystwx13:
My thinking is that this is designated as a tropical depression tomorrow afternoon. It further intensifies to become a tropical storm on Thursday, and approaches hurricane status by the time it reaches the Leeward Islands over the weekend. After entering the Caribbean, it weakens slightly to a midgrade tropical storm and enters the West Caribbean.

To be continued...
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Quoting JrWeathermanFL:

Not on the blog thats for sure.
Banned?.
Member Since: August 14, 2010 Posts: 10 Comments: 17151
1419. yqt1001
I've been away for a few days and am tethering so I don't want to use tons of data loading other pages. I see 99L at 50% on NHC and would like some more information on what it may do and how strong it will be in the future.
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Generally Caribbean shear isn't that bad... The only questionable area is around Jamaica as I said... That 40 doesn't look too friendly:

Member Since: February 11, 2012 Posts: 83 Comments: 7845
Quoting washingtonian115:
Where is WXGeekVA?.

Not on the blog thats for sure.
Member Since: July 19, 2011 Posts: 12 Comments: 2459
Quoting RetainingH2O:
Have you ever noticed that tropical storms seem to form in Alphabetical order each year?
This has to be more than a coincidence. Every year... a list of names is created and the storms somehow manage to form in order. It's almost uncanny!

LMAO.
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Have you ever noticed that tropical storms seem to form in Alphabetical order each year?
This has to be more than a coincidence. Every year... a list of names is created and the storms somehow manage to form in order. It's almost uncanny!
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1413. JRRP
well i said red color for today... but 50% is not bad
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Quoting KoritheMan:


Do a blog for god's sake. I miss them.

I'll do one later, just for you. ;)
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As I said people shear will not be a problem for 99L in the caribbean and I said it over and over again
Member Since: June 13, 2009 Posts: 2 Comments: 12180
Where is WXGeekVA?.
Member Since: August 14, 2010 Posts: 10 Comments: 17151
Quoting TropicalAnalystwx13:
My thinking is that this is designated as a tropical depression tomorrow afternoon. It further intensifies to become a tropical storm on Thursday, and approaches hurricane status by the time it reaches the Leeward Islands over the weekend. After entering the Caribbean, it weakens slightly to a midgrade tropical storm and enters the West Caribbean.

To be continued...


Do a blog for god's sake. I miss them.
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Quoting stormchaser19:
I don't understand

All the ensemble members start their runs using slightly different conditions, so they tend to spread out... Draw a line through the middle of them and generally that's where it goes.
Member Since: February 11, 2012 Posts: 83 Comments: 7845
Quoting MAweatherboy1:
Shear seems to be lowering.
Member Since: August 14, 2010 Posts: 10 Comments: 17151
Quoting Stormchaser2007:
18z HWRF brings 99L into the ECARB as a decent tropical storm.

Odd.


Why is that odd?
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Quoting washingtonian115:
Some of the models are starting to pick up on a more favorable environment in the caribbean.odd?..Not odd at all.Still a long ways out.
Trades arent as strong as most thought and it should be a TD tomorrow maybe 11am.
Member Since: March 16, 2012 Posts: 127 Comments: 7952
Quoting KoritheMan:


Uh, that's what they're supposed to do. That's why they're called ensembles.


ok
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My thinking is that this is designated as a tropical depression tomorrow afternoon. It further intensifies to become a tropical storm on Thursday, and approaches hurricane status by the time it reaches the Leeward Islands over the weekend. After entering the Caribbean, it weakens slightly to a midgrade tropical storm and enters the West Caribbean.

To be continued...
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Quoting stormchaser19:


GFS Ensemble take other path of the head model


Uh, that's what they're supposed to do. That's why they're called ensembles.
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Quoting Stormchaser2007:
18z HWRF brings 99L into the ECARB as a decent tropical storm.

Odd.


Why would that be odd?
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Member Since: February 11, 2012 Posts: 83 Comments: 7845
Quoting KoritheMan:


You don't understand what?


GFS Ensemble take other path of the head model
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Quoting Stormchaser2007:
18z HWRF brings 99L into the ECARB as a decent tropical storm.

Odd.
A 995mb storm at 126 hrs in the E caribbean.
Member Since: March 16, 2012 Posts: 127 Comments: 7952
Some of the models are starting to pick up on a more favorable environment in the caribbean.odd?..Not odd at all.Still a long ways out.
Member Since: August 14, 2010 Posts: 10 Comments: 17151
Quoting stormchaser19:
I don't understand

I dont get it, you dont understand what? The gfs and gfs ensemble members differ.
Member Since: March 16, 2012 Posts: 127 Comments: 7952
18z HWRF brings 99L into the ECARB as a decent tropical storm.

Odd.

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Quoting stormchaser19:
I don't understand


You don't understand what?
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I don't understand
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Member Since: March 16, 2012 Posts: 127 Comments: 7952
Quoting ncstorm:


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




Buffet Night?!!!!

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thanks bluestorm and kman! that one on the website you linked bluestorm looks awesome... reminds me of andrew!
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SPECIAL FEATURES...

A TROPICAL WAVE IS ALONG 16N40W TO A 1010 MB SURFACE LOW AT
10N41W. THE WAVE/LOW IS MOVING W AT ABOUT 10-15 KT. THE WAVE IS
FAIRLY LOW AMPLITUDE ALIGNING WITH AN EQUALLY LOW AMPLITUDE
SURGE IN TOTAL PRECIPITABLE WATER. HOWEVER...AN ANALYSIS OF THE
SAHARAN AIR LAYER CONTINUES TO SHOW A CLEARING IN THE WIDESPREAD
DUST NEAR THE WAVE AXIS INDICATING ITS PRESENCE. CONVECTION HAS
INCREASED AROUND THE LOW CENTER FROM 24 HOURS AGO. CURRENTLY
SCATTERED MODERATE/STRONG CONVECTION IS MAINLY W OF THE SYSTEM
FROM 7N-11N BETWEEN 41W-46W. ENVIRONMENTAL CONDITIONS ARE
CONDUCIVE FOR SLOW DEVELOPMENT OF THIS SYSTEM.

8PM EDT Trop Discussion
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Quoting MAweatherboy1:

Pat could you outline your polling schedule for us?


I have heard a rumor that Pat does pole.... on February 29th... but who knows?
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The Convective Coupled Kelvin Wave has progressed nicely today and is the reason why the tropical wave over the Greater Antilles has blown up. Once that reaches 99L, it should provide the spark that it needs to become a tropical cyclone given that 99L already has some low level structure to work with. Shear should be low in the short term and SST's should approach 28.5 C. I think it has a decent chance of becoming a tropical storm before reaching the islands.

Thereafter, it should degenerate into an open wave due to unfavorable shear/trades and traverse the Caribbean. It might have a chance in the western Caribbean or Gulf (like the ECMWF EPS control suggests), but that's 8-10 days away.

Right now, I'd say there's a high chance of this becoming a tropical cyclone in the next 72 hours.



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Quoting taco2me61:

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)



I couldn't resist. Just funnin' ya!
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Quoting Bluestorm5:


Weak E. No more than 80 MPH.


Imo It will be a moderate tropical storm at about 47.5 Knots.
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Quoting MAweatherboy1:

Pat could you outline your polling schedule for us?

Sunday: Fresca/No polling
Monday: No polling
Tuesday: No polling
Wednesday: Fresca/No polling
Thursday: No polling
Friday: No polling
Saturday: Fresca/No polling
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Quoting wxchaser97:
Even with DMIN and detaching from the ITCZ 99L is still looking decent.

very true
with DMAX coming its going to blow like a nuke I say 2am TWO red 70%

Quoting bajelayman2:
99L is in a similar position to Ivan. If it can pull off the ICTZ fully it will develop quickly, due to high SST's and low shear, no saharan dust to impede.

Just my layman's opinion.



so very true

Member Since: June 13, 2009 Posts: 2 Comments: 12180
Quoting Hurricane1956:
I'm actually more worried about the tropical wave over the Dominican Republic than 99L at this point,here in Miami we can get some very nasty weather from this system coming from the East, at least a lot of rain and wind for the weekend,it looks very impressive,I know the Hurricane Center is giving 0% of development but this time of year you never know??,again at the very minimum we should get some bad weather from Friday-Sunday (IMO).


Bad weather is good weather, unless it's severe weather (IMO).

More Clouds, Less sun!
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i nevere poll on the weekends
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Quoting TropicalAnalystwx13:
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.


Weak E. No more than 80 MPH.
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1375. ncstorm
HWRF 18z
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Quoting Patrap:


Why they could always Poll us here.

Save fo me as I never Poll on a Tuesday.

Pat could you outline your polling schedule for us?
Member Since: February 11, 2012 Posts: 83 Comments: 7845
Quoting Patrap:


Why they could always Poll us here.

Save fo me as I never Poll on a Tuesday.

You know you want to, Pat.
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1372. ncstorm
Quoting Pocamocca:

The first thing that popped into my head when I read your post was Tomas. That thing got ramped up to category 2 strength in a heartbeat.



Yeah I believe Levi posted that image yesterday too..
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99L is in a similar position to Ivan. If it can pull off the ICTZ fully it will develop quickly, due to high SST's and low shear, no saharan dust to impede.

Just my layman's opinion.

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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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