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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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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Pileus clouds, created by a layer of ice crystals and thunderstorms, turn heads yesterday
Member Since: May 23, 2012 Posts: 0 Comments: 4681
2069. pottery
Quoting SLU:
RED ALERT! RED ALERT!

Well, this looks like fun.... !

Not sure I want any fun though...

Good Morning all.
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cv.system.could.be.a.bad.girl...
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The GFS looked kinda interesting at the 174 hr frame, can't load frames after that. Anyone now what it does with storm after that
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Quoting TropicalAnalystwx13:
Red alert.
..but your icon shows "yellow" alert? Did you issue a red alert when infact the conditions did not exist? How do you explain that one?
Member Since: May 16, 2010 Posts: 0 Comments: 1472
butterfly.island.is.a.magnet
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2063. WxLogic
Hmm... 60% already. Was expecting 60% and above by tonight.
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700MB


500MB


200MB

Member Since: May 23, 2012 Posts: 0 Comments: 4681
2061. ncstorm
so what we got..a shift back to the NW?
Member Since: August 19, 2006 Posts: 13 Comments: 15674
Member Since: May 23, 2012 Posts: 0 Comments: 4681
TROPICAL WEATHER OUTLOOK

800 AM EDT WED AUG 1 2012


SHOWERS AND THUNDERSTORMS ASSOCIATED WITH AN AREA OF LOW PRESSURE
CONTINUE TO SHOW SIGNS OF ORGANIZATION. ENVIRONMENTAL CONDITIONS
ARE CONDUCIVE FOR GRADUAL DEVELOPMENT OF THIS LOW...AND THIS SYSTEM
HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS AS IT MOVES WESTWARD AT 15 TO 20 MPH.
INTERESTS IN THE WINDWARD ISLAND SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM
.




Member Since: February 11, 2012 Posts: 0 Comments: 9731
2057. SLU
RED ALERT! RED ALERT!
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Red alert.
Member Since: July 6, 2010 Posts: 113 Comments: 32275
60%
Member Since: February 11, 2012 Posts: 0 Comments: 9731
Good morning, y'all.
Member Since: August 1, 2011 Posts: 28 Comments: 8030
2052. ryang
000
ABNT20 KNHC 011152
TWOAT

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

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

SHOWERS AND THUNDERSTORMS ASSOCIATED WITH AN AREA OF LOW PRESSURE
LOCATED ABOUT 1000 MILES EAST OF THE SOUTHERN WINDWARD ISLANDS
CONTINUE TO SHOW SIGNS OF ORGANIZATION. ENVIRONMENTAL CONDITIONS
ARE CONDUCIVE FOR GRADUAL DEVELOPMENT OF THIS LOW...AND THIS SYSTEM
HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A TROPICAL CYCLONE

DURING THE NEXT 48 HOURS AS IT MOVES WESTWARD AT 15 TO 20 MPH.
INTERESTS IN THE WINDWARD ISLAND SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM.

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

$$
FORECASTER PASCH
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right red 60%
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2050. ryang
60%
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2049. ncstorm
Good Morning Everyone!!

Member Since: August 19, 2006 Posts: 13 Comments: 15674
Quoting RidingTheStormOut:
Good Morning Friends, Back for the season, amateur noob that I be, I only come on during season. Thanks in advance everyone, for all the neat info I osmose during the season. Lots of folks with lots of cool info. Amateur point of view.... The Caribbean will be the graveyard for 99L.


about 4 storms late...lol
:)
Member Since: February 11, 2012 Posts: 0 Comments: 9731
Quoting Pocamocca:

Thanks, man. That's the one I was thinking of then--the CMC. Interesting the Euro shoots 99L up that far north though on the latest run.


It could go anywhere right now so that is why the next 2 to 3 days are so key because if 99L strengthens more quickly then we will see a more northern track across the northern Caribbean vs. the southern track of the GFS. either one could play out at this point.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
2046. SLU
Quoting luigi18:


wow that's is no good for PR !


It's only a matter of which islands will get hit. No chance of this missing us.
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Invest 99L Continues To Become More Organized, Likely To Develop Into Tropical Storm Ernesto & Will Affect Barbados & The Lesser Antilles On Friday; Track & Intensity After That Remains In Question
Wednesday, August 1, 2012 5:42 am
by Rob Lightbown

Invest 99L, which is located a little over 1000 miles east-southeast of the Windward Islands has become better organized over the past 24 hours. Overnight and early morning satellite loops show deeper convection firing near the low pressure system. Additionally, this deeper convection has caused 99L to become better organized just in the last few hours. Also, environmental conditions appear to be favorable and remain favorable for this system to continue organizing and developing. I still think that Invest 99L will become a tropical depression as early as late today or early Thursday and then Tropical Storm Ernesto by late Thursday or early Friday.

The consensus track guidance as well as the latest NAM and GFS model guidance forecasts that 99L will remain on a slightly north of due west track over the next several days and pass very near or just south of Barbados during the day Friday and then across the Windward Islands towards later Friday. From there, the consensus track guidance and the GFS model (even though it really doesn’t develop it) keeps 99L on a track that takes it across the southern Caribbean this weekend.

The latest European model guidance has shifted significantly northward and forecasts 99L to track across the islands of Martinique and Dominica on Friday and then pass just south of Puerto Rico as a weakening system that opens up to a tropical wave by Saturday. The European model then forecasts 99L to track across the Bahamas from Sunday to Tuesday as a tropical disturbance. One item to point out in the European model guidance is that it forecasts another organizing tropical disturbance to begin approaching the Lesser Antilles during the weekend of August 11th and 12th.

So, here are my thoughts: I do think that it is likely that Invest 99L will become a tropical depression by late today or more likely during Thursday and then be upgraded from there to Tropical Storm Ernesto by Friday. As for a track, based on the track consensus guidance and the general motion of 99L, I think that a track either over or just north of Barbados seems quite possible during the day Friday as a 40 to 45 mph tropical storm. From there, I think we will see 99L track near the island of St. Lucia by late Friday as a 45 mph tropical storm. Now, it should be pointed out that this is an early “guess” based on all of the available data and this track idea can and likely will change.

Beyond the Lesser Antilles, I think that Invest 99L will track across the Caribbean and may not intensify at all due to less than favorable environmental conditions in the Caribbean.

All interests in the Lesser Antilles, especially those of you in Barbados and from the islands of Dominica southward to Grenada should be ready for tropical storm conditions on Friday with wind gusts to 50+ mph, heavy rainfall and rough seas. Do not wait for Invest 99L to be named to prepare for it.

I am monitoring Invest 99L closely and I will keep you all updated on the latest.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting Pocamocca:

Still calling for that cat 4 by the islands....

LOL

no I'm not and wasn't calling one neither
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2041. luigi18
Quoting SLU:


What a difference a night makes.


wow that's is no good for PR !
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Quoting Pocamocca:

Euro has been very consistent, no?


It had a weak system in the Gulf yesterday and today it's over FL. Really the only consistant model has been the CMC or GGEM model.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting aspectre:
2004 caribbeantracker01: It would be TD.3
If not, someone tell me if all the systems were topical depressions when they formed?


TropicalDepressions are numbered in keeping with the TropicalCyclone number,
and not by how many TDs there were before the latest one appears.
The next Atlantic TropicalCyclone will be AL05: so if 99L becomes a TD, it'll be called TropicalDepressionFive
or TD.5 for short

thank you about time someone explained it to carib tracker

Quoting Pocamocca:

No, that's okay. I'll just here for those outlooks to be posted en masse right here.

Thanks, Kid.

ok by the way I am not a kid so don't call me kid
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Here is this mornings discussion by Crown Weather.

Link
Member Since: April 29, 2009 Posts: 75 Comments: 14326
2036. luigi18
Quoting SLU:


It will most likely pass south of PR but the models has shifted a bit north this morning so PR could get some more weather from it if this happens.


Thanks!
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2035. SLU
Quoting Tropicsweatherpr:


Yes,that 00z Euro was very interesting as it shifted north and tracks it closer to PR.


What a difference a night makes.
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2004 caribbeantracker01: It would be TD.3
If not, someone tell me if all the systems were topical depressions when they formed?


TropicalDepressions are numbered in keeping with the TropicalCyclone number,
and not by how many TDs there were before the latest one appears.
The next Atlantic TropicalCyclone will be AL05.
So if 99L becomes a TD, it'll be called TropicalDepressionFive, or TD.5 for short.
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Member Since: September 30, 2007 Posts: 9 Comments: 15940
Going now, c you guys later, thanks!!
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time people should start to hit F5 on NHC
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Quoting mitthbevnuruodo:



It totally looked like it popped a bit north to me too when I first looked this morning.


The westPac typhoons look pretty awesome in unison over there. The inland area where they're both looking to end up over is going to have some bad problems. Hope they get caught up in a front and move along quickly

yeah I know its convection increasing in that area because shear is falling
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Quoting GeoffreyWPB:


Looks like an uptick in movement there?
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Quoting stoormfury:
bajelayman 2 is this weekend crop over festival?


Yes. Foreday Morning (a casual street jam early morning in the dark) is Saturday. Other events from Friday night and then Grand Kadooment next week early.

Wet, wet, wet!?
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Quoting stormpetrol:
Good Morning , Is the center of 99L around 11N/47W?

10.2N 46.0W
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Quoting wunderkidcayman:

nah it at 10.1N 45.8W moving W



It totally looked like it popped a bit north to me too when I first looked this morning.


The westPac typhoons look pretty awesome in unison over there. The inland area where they're both looking to end up over is going to have some bad problems. Hope they get caught up in a front and move along quickly
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Quoting wunderkidcayman:

the CMC is the outlier


So you are saying the Euro is as well then right? Both have FL landfall in 8 to 9 days.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
2021. WxLogic
I would keep 99L at 50% until it clears 50W. If it's successful at completely detaching from the ITCZ, sustaining convection, and fighting some shear around 50W then I would bump it up to 70%.
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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.