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 ProgressivePulse:


Actually starts to close it off at 36hrs



Does @ 60hrs



Looks like a developing low east of TCI. Should be taking shape pretty quickly if the NAM has a low trying to close off in 36hrs.
NAM is not the only one picking up on it, check out the GFS:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting ProgressivePulse:


Actually starts to close it off at 36hrs



Does @ 60hrs



Looks like a developing low east of TCI. Should be taking shape pretty quickly if the NAM has a low trying to close off in 36hrs.


Well heck, maybe that 0% may have been overly optimistic!
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Quoting unknowncomic:
00z nam model showing a deepening low in bahamas @ 82 hrs


Actually starts to close it off at 36hrs



Does @ 60hrs



Looks like a developing low east of TCI. Should be taking shape pretty quickly if the NAM has a low trying to close off in 36hrs.
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Quoting KoritheMan:


Yeah. I didn't say four major hurricanes is a common motif. :P


Last time I started comparing this year to 2004 (a weak el nino starting) and making doom predictions the activity shut down and I have been sulking since (right after Debby when we had a bunch of yellow circles). So I am not making any new doom predictions until I see the white of their eyes! (hurricanes that is).
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99l is starting to really get its act together.
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Quoting nigel20:
Jamaica was spared most of the effects of hurricane Ivan. Ivan wobble to the west just before impact.



Woow.....That year the Ridge was very very strong.
Member Since: June 20, 2012 Posts: 0 Comments: 2169
Quoting aspectre:
1July12pmGMT's StormStatus has been re-evaluated&altered from DisturBance to LOw
1July6pmGMT's StormStatus has been re-evaluated&altered from DisturBance to LOw
Its MinimumPressure has been re-evaluated&altered from 1010millibars to 1009millibars

9.6n41.3w has been re-evaluated&altered
9.5n41.3w - 9.7n43.0w are now the most recent positions
Derived from (NHC) ATCF data for 99L for 1August12amGMT:
MinimumPressure had held at 1009millibars
MaximumSustainedWinds had held at 25knots(29mph)46km/h
Its vector had held to 276.9°West at 19.5mph(31.3km/h)

For those who like to visually track 99L's path...
SLU is SaintLucia :: BGI is Barbados :: CRU is Carriacou :: TAB is Tobago

The Easternmost dot on the connected line-segments is where 99L became a LOw
The Easternmost dot on the longest line is 99L's most recent position

The longest line is a straightline projection through 99L's 2 most recent positions to a coastline.
On 1August12amGMT, 99L was headed toward passing over KingsBay,Tobago in ~2days9hours from now

Copy&paste axa, slu, bgi, cru, tab, 9.3n39.6w- 9.5n41.3w- 9.7n43.0w, 9.5n41.3w-11.25n60.554w into the GreatCircleMapper for more information
The previous mapping for comparison.

about time you show up
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99L is starting to come out of diurnal minimum. Should expect an increase in thunderstorm activity in response.

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting nigel20:
Jamaica was spared most of the effects of hurricane Ivan. Ivan wobble to the west just before impact.

So of the past storms that you have been through which one gave you the worst weather?
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting nigel20:
Jamaica was spared most of the effects of hurricane Ivan. Ivan wobble to the west just before impact.

I remember Ivan. Caused flooding and tornadoes up in Atlanta. Got off school for 3 days because roads where blocked and the power was out.
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Quoting Huracaneer:


Yes, but add to Ivan, Charley, Frances and Jeanne and it made for a very BAD year for Florida. Charley is the closest brush Tampa Bay has had with a major in a very long time.


Yeah. I didn't say four major hurricanes is a common motif. :P
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Quoting nigel20:
Jamaica was spared most of the effects of hurricane Ivan. Ivan wobble to the west just before impact.


yeah and put the worst one us
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Quoting KoritheMan:


At this point we're so used to storms avoiding the Gulf that we won't know what to do when one finally does.
This is true, which is why we need the wind shear in the Caribbean to kill it off or the Subtropical Ridge to hold strong on the southern flank and keep it going west.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
1July12pmGMT's StormStatus has been re-evaluated&altered from DisturBance to LOw
1July6pmGMT's StormStatus has been re-evaluated&altered from DisturBance to LOw
Its MinimumPressure has been re-evaluated&altered from 1010millibars to 1009millibars

9.6n41.3w has been re-evaluated&altered
9.5n41.3w - 9.7n43.0w are now the most recent positions
Derived from (NHC) ATCF data for 99L for 1August12amGMT:
MinimumPressure had held at 1009millibars
MaximumSustainedWinds had held at 25knots(29mph)46km/h
Its vector had held to 276.9degreesWest at 19.5mph(31.3km/h)

For those who like to visually track 99L's path...
SLU is SaintLucia :: BGI is Barbados :: CRU is Carriacou :: TAB is Tobago

The Easternmost dot on the connected line-segments is where 99L became a LOw
The Easternmost dot on the longest line is 99L's most recent position

The longest line is a straightline projection through 99L's 2 most recent positions to a coastline.
On 1August12amGMT, 99L was headed toward passing over KingsBay,Tobago in ~2days9hours from now

Copy&paste axa, slu, bgi, cru, tab, 9.3n39.6w- 9.5n41.3w- 9.7n43.0w, 9.5n41.3w-11.25n60.554w into the GreatCircleMapper for more information
The previous mapping for comparison.
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Quoting KoritheMan:


Ivan by itself wasn't actually that unusual. A Category 3 hurricane hitting the US is fairly common (save for the last few years).


Yes, but add to Ivan, Charley, Frances and Jeanne and it made for a very BAD year for Florida. Charley is the closest brush Tampa Bay has had with a major in a very long time.
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00z nam model showing a deepening low in bahamas @ 82 hrs
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Quoting GTcooliebai:
Boy if this thing develops rapidly, I'm looking at the large scale synoptic pattern across the CONUS and it shows a trough coming down from the Great Lakes and moving towards the Southeast, if the system has gained enough latitude it could get caught and brought up into the GOM.


At this point we're so used to storms avoiding the Gulf that we won't know what to do when one finally does.
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Quoting GTcooliebai:
Maybe indicating its lift out of the ITCZ?



If anything, we should probably expect a decrease in convection once it moves out of the ITCZ. Too much dry air around, but not enough to kill it unless shear gets involved.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1802. JLPR2
Quoting MississippiWx:


Red at 2AM, probably 60%. I'm liking the looks of 99L.


I'm thinking it stays the same. 50%
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1801. nigel20
Jamaica was spared most of the effects of hurricane Ivan. Ivan wobble to the west just before impact.

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Quoting KoritheMan:


From 99L? I'd say about 60%.


ok thanks
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Quoting wunderkidcayman:
99L cooling cloud tops new AVN sat image came out (03:45 UTC) red spots are growing
Maybe indicating its lift out of the ITCZ?

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Quoting Huracaneer:


Yes evil is probably not a good word, "terrible" is much more appropriate :). Ivan was a nasty one in Fl and while I don't think 99L has a chance of being like Ivan, it still gives me the heebie-jeebies any time somebody mentions the "I" word.


Ivan by itself wasn't actually that unusual. A Category 3 hurricane hitting the US is fairly common (save for the last few years).
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Quoting ilovehurricanes13:
LOOK AT 55 WEST AND 10 north WInd shear WENT UP 5 KNOWS!!


Yes,but 99L is nearly 45W
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99L cooling cloud tops new AVN sat image came out (03:45 UTC) red spots are growing
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Quoting KoritheMan:


Second night in a row we've disagreed, Drew. You sure you aren't holding something against me? ;)


Hehe. Nothing against you, but I've also been correct on the last 3 TWOs. :-D I'm bragging because I always miss the percentage.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Boy if this thing develops rapidly, I'm looking at the large scale synoptic pattern across the CONUS and it shows a trough coming down from the Great Lakes and moving towards the Southeast, if the system has gained enough latitude it could get caught and brought up into the GOM.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
1793. KEEPEROFTHEGATE (Mod)
Fleet Weather Center Norfolk Virginia

No Active Atlantic Tropical Warnings
August-01-12, 12:15:01 AM | Maritime.CDO@navy.mil (FWC-N CDO)
As of Wed, 01 Aug 2012 04:15:01 GMT
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Nam in 60hrs. Starts to look interesting at 36hrs.

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Quoting MississippiWx:


Red at 2AM, probably 60%. I'm liking the looks of 99L.


Second night in a row we've disagreed, Drew. You sure you aren't holding something against me? ;)
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1790. 19N81W
Not that I wish destructive storms on anyone but is it me but how often do we see them knocking on our doorsteps recently?.....wasn't climate change supposed to increase them? Not to take it off thread but given the pic gearst posted....
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Quoting robert88:
99L has a rough road ahead. You can clearly see the wind shear. ^


Wind shear is definitely going to be an issue for 99L once it gets into the Caribbean, especially into the Central and Western Caribbean according to the GFS.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Anyone that has basic knowledge of the tropics can see the shear has picked up near 99L. Satellite shows it well.
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Quoting ilovehurricanes13:
LOOK AT 55 WEST AND 10 north WInd shear WENT UP 5 KNOWS!!


Yeah you are right, but it only has to get through a little bit of shear to get in the clear.
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99L is definitely becoming its own entity and should be fully departed from the ITCZ by tomorrow. A tropical cyclone is definitely possible within the next 24 hours.

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting ilovehurricanes13:
LOOK AT 55 WEST AND 10 north WInd shear WENT UP 5 KNOWS!!

dude chill out it is droping you are starting to sound like jason now
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Quoting KoritheMan:


I really hate when people label hurricanes as "evil". They don't have a mind of their own. I know what you mean, it's just a small pet peeve of mine. ;)


Yes evil is probably not a good word, "terrible" is much more appropriate :). Ivan was a nasty one in Fl and while I don't think 99L has a chance of being like Ivan, it still gives me the heebie-jeebies any time somebody mentions the "I" word.
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1783. nigel20
Quoting Gearsts:

Hugo was a very powerful hurricane...It came one year after Jamaica was ravaged by the infamous hurricane Gilbert.
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99L has a rough road ahead. You can clearly see the wind shear. ^
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1780. 19N81W
Just rain please and hopes that it doesn't do something stupid in the gulf to hurt our friends up there....just rain for Texas and other areas that need it....I kinda think it's going to die in the Caribbean but when rain is in such need especially in the states one will take a minimal storm for it.....funny hoe mother nature never does what we ask her to do!
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Quoting Huracaneer:


It would really have to thread the needle to take advantage of that, but possible (hence the near 0% chance). Of course the shear over Fl right now is pretty high, so it would probably be short lived if anything managed to form.



NHC sees a small window, hence the 0%. No way this develops 48hrs from the 8pm. However, tomorrow you could see chances go up as we approach the small window. The COL area is to remain with fluctuation between it and the ATL Ridge with respect to the Peninsula. Never know.
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Quoting stormchaser19:


That will change in the next hours,i think since the 99L is not convecting in the past hours the NHC maybe stay in 50% the question is RED OR Stay with orange?

if they do that I know that at the 8am it will be at 70% or 80% and TD at 11am
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GFS 102 hrs. nice trough over the Great Lakes:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
1776. nigel20
Quoting KoritheMan:


I really hate when people label hurricanes as "evil". They don't have a mind of their own. I know what you mean, it's just a small pet peeve of mine. ;)

Agreed.
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Quoting KoritheMan:


They will stay with orange.


Red at 2AM, probably 60%. I'm liking the looks of 99L.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1774. KEEPEROFTHEGATE (Mod)
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Quoting msphar:
Looking back to Ivan 2004, by this Longitude Ivan was a cat 2 and growing more evil everyday. Tonight, I have concerns for the survival of 99L what a difference a dacade (or thereabouts) makes.


I really hate when people label hurricanes as "evil". They don't have a mind of their own. I know what you mean, it's just a small pet peeve of mine. ;)
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Quoting stormchaser19:


That will change in the next hours,i think since the 99L is not convecting in the past hours the NHC maybe stay in 50% the question is RED OR Stay with orange?


They will stay with orange.
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1771. msphar
Looking back to Ivan 2004, by this Longitude Ivan was a cat 2 and growing more evil everyday. Tonight, I have concerns for the survival of 99L what a difference a decade (or thereabouts) makes.
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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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