African tropical wave 99L has potential to develop

By: Dr. Jeff Masters , 3:10 PM GMT on July 30, 2012

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The first African tropical wave of 2012 with a potential to develop is Invest 99L, located in the Eastern Atlantic near 9°N 36°W, midway between the Lesser Antilles Islands and the coast of Africa. Visible satellite loops show a large area of the surrounding atmosphere has a pronounced counter-clockwise spin, though there is no surface circulation. The disturbance's heavy thunderstorm activity is pretty sparse, but appears to be slowly increasing. Water vapor satellite loops show that 99L has a reasonably moist environment, and the latest Saharan air layer analysis shows that the dry air from the Sahara lies well to the north of 99L. 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 for the next five days, and ocean temperatures will remain near 28°C, according to the 8 am EDT run of the SHIPS model. 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, with the storm reaching the Lesser Antilles Islands on Saturday, August 3. NHC gave 99L a 20% chance of developing into a tropical depression by Wednesday morning. I expect the storm will have trouble with dry air at times this week as it crosses the Atlantic, but I 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 night. The long-range fate of 99L is uncertain, but a trough of low pressure is expected to be present over the Eastern U.S. early next week, which would be capable of turning 99L more to the northwest.

Hot in the Central U.S.
The heat in America's heartland continued on Sunday, with Wichita, KS hitting 111°F, just 3° short of their all-time hottest temperature of 114° set on 8/12/1936. Other notable highs on Sunday:

111° Coffeyville, KS
111° Winfield, KS
110° Chanute, KS
110° Parsons, KS
109° Joplin, MO (all-time record is 115° on July 14, 1954)

The low temperature in Tulsa, Oklahoma this Monday morning dropped to only 88°F. This is the all-time warmest low temperature in the city since record keeping began in 1905. The previous record warmest minimum temperature was 87°F set on August 2, 2011 and July 16, 1980. The high in Tulsa Monday - Wednesday is expected to reach 110° - 111°, close to the city's all-time hottest temperature of 115° set on August 10, 1936.

Jeff Masters

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Quoting AtHomeInTX:


That can't be good.



Very good for drought areas
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Quoting LargoFl:
..whew keep an eye on that storm for us,we in florida are going to be dealing with these severe rain storms most of this week,attention is going to be on them and the possible flooding etc


Oh no. Hope it doesn't get too bad. Y'all don't need a wave on top of that.
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1668. LargoFl
BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE HUNTSVILLE AL
554 AM CDT TUE JUL 31 2012

THE NATIONAL WEATHER SERVICE IN HUNTSVILLE HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
NORTHEASTERN JACKSON COUNTY IN NORTHEAST ALABAMA...

* UNTIL 645 AM CDT

* AT 552 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL...AND
DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED NEAR
RUSSELL CAVE NATIONAL MONUMENT...OR ABOUT 7 MILES NORTHWEST OF
BRIDGEPORT...AND MOVING SOUTH AT 25 MPH.

* LOCATIONS IMPACTED INCLUDE...
RUSSELL CAVE NATIONAL MONUMENT...
LONG ISLAND...
BRIDGEPORT...BASS...
STEVENSON...
FABIUS...HIGDON...
FACKLER...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

THIS IS A DANGEROUS STORM. IF YOU ARE IN ITS PATH...PREPARE
IMMEDIATELY FOR DAMAGING WINDS...DESTRUCTIVE HAIL...AND DEADLY CLOUD
TO GROUND LIGHTNING. PEOPLE OUTSIDE SHOULD MOVE TO A SHELTER...
PREFERABLY INSIDE A STRONG BUILDING BUT AWAY FROM WINDOWS.



LAT...LON 3483 8563 3480 8563 3478 8592 3499 8593
3499 8586 3499 8560 3498 8560 3486 8558
TIME...MOT...LOC 1053Z 353DEG 20KT 3503 8579


SL
Member Since: August 6, 2011 Posts: 4 Comments: 37103
1667. LargoFl
Quoting AtHomeInTX:


The 6z GFS does send it into the gulf via Florida. Seems to persist awhile anyway. Link

..whew keep an eye on that storm for us,we in florida are going to be dealing with these severe rain storms most of this week,attention is going to be on them and the possible flooding etc
Member Since: August 6, 2011 Posts: 4 Comments: 37103
Quoting LargoFl:
..............................oh boy


That can't be good.
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Quoting islander101010:
cat1...not.the.end.of.the.world..hispanola.system .is.persistant..wait.to.it.enters.the.gulf


The 6z GFS does send it into the gulf via Florida. Seems to persist awhile anyway. Link

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1664. LargoFl
..............................oh boy
Member Since: August 6, 2011 Posts: 4 Comments: 37103
1663. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 37103
1662. LargoFl
Quoting RTSplayer:


Yup. Was watching the PR radar earlier, and saw isolated rainfall rates of 4 inches per hour, with several cells above 2 inches per hour.
wow thats alot of rain but i think someone said they were needing rain, this should help them out if they dont get too much flooding, the blob isnt a fast mover
Member Since: August 6, 2011 Posts: 4 Comments: 37103
1661. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 37103
Quoting LargoFl:
.............................that blob down by the Islands is still there


Yup. Was watching the PR radar earlier, and saw isolated rainfall rates of 4 inches per hour, with several cells above 2 inches per hour.
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morning
99L is slowly organising and could become a depression by late wednesday. the system is moving west with an ULAC dirctly over the disturbance.This will allow proper ventilation for the system. there is strong 850mb vorticity as well as good convergence and divergence. the system will move slightly north of west the next 48 hrs with a more wnw turn there after. 99L is expected to become tropical storm Ernesto some time friday. and affect barbados and the central lesser antilles with tropical storm force winds, heavy rainfall and rough seas ,starting friday evening and continuing on saturday. residence of these islands should monitor this developing situation.
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1658. LargoFl
yep,the bad weather is starting already, its going to be a very interesting day here in the southeast......................BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
616 AM EDT TUE JUL 31 2012

THE NATIONAL WEATHER SERVICE IN PEACHTREE CITY HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
DADE COUNTY IN NORTHWEST GEORGIA
WESTERN WALKER COUNTY IN NORTHWEST GEORGIA

* UNTIL 715 AM EDT

* AT 615 AM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZED HAIL...AND
DAMAGING WINDS UP TO 60 MPH. THIS STORM WAS LOCATED 17 MILES
NORTHWEST OF TRENTON...MOVING SOUTHEAST AT 25 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
LOOKOUT MOUNTAIN...LAFAYETTE AND CHICKAMAUGA.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IN ADDITION TO LARGE HAIL AND DAMAGING WINDS...CONTINUOUS CLOUD TO
GROUND LIGHTNING IS OCCURRING WITH THIS STORM. MOVE INDOORS
IMMEDIATELY! REMEMBER...IF YOU CAN HEAR THUNDER...YOU ARE CLOSE
ENOUGH TO BE STRUCK BY LIGHTNING.

IF YOU SEE WIND DAMAGE...HAIL OR FLOODING...WAIT UNTIL THE STORM HAS
PASSED...AND THEN CALL THE NATIONAL WEATHER SERVICE TOLL FREE AT 1 8
6 6 7 6 3 4 4 6 6. YOU CAN ALSO TWEET YOUR REPORT USING HASHTAG GAWX.



LAT...LON 3499 8528 3498 8526 3486 8526 3485 8520
3479 8520 3466 8533 3488 8560 3498 8561
3499 8560
TIME...MOT...LOC 1016Z 307DEG 21KT 3507 8566
Member Since: August 6, 2011 Posts: 4 Comments: 37103
Quoting MAweatherboy1:
Good morning... CMC last night:

cat1...not.the.end.of.the.world..hispanola.system .is.persistant..wait.to.it.enters.the.gulf
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1656. LargoFl
.............................that blob down by the Islands is still there
Member Since: August 6, 2011 Posts: 4 Comments: 37103
The 6z GFS keeps 99L through 192 hours, then dissipates it:

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1654. LargoFl
...................7 day forecast for the Tampa Bay area..looks like another day like yesterday alright
Member Since: August 6, 2011 Posts: 4 Comments: 37103
Slowly but surely, 99L is organizing... Probably 30% at 8AM but IMO should be 40% because of all this convection:

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Good morning... CMC last night:

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The usual ASCAT wind products page hasn't been working for the past day. This seems to be OK:

Link
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that water surely is boiling hot! waters ahead of 99L is very warm and hot!
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since this shear is coming down in the carribean this thing should intensify rather quickly!
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1648. hydrus
Quoting BahaHurican:
Hey, ya'll... how's our invest doing this fine a.m.?
Slowly but surely organizing.
Member Since: September 27, 2007 Posts: 1 Comments: 20547
1647. SLU
the convection has increased with 99L but it still looks very blobbish
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Quoting aspectre:
1641 allancalderini: Does the system near BC dissipate?

What's 'BC'? BajaCalifornia?
sorry I am too sleepy I mean NC.
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1641 allancalderini: Does the system near BC dissipate?

What's 'BC'? BajaCalifornia?
Member Since: August 21, 2007 Posts: 0 Comments: 4860
1644. LargoFl
......................Good Morning Folks..still at 20% this morning..nothing new with it so far
Member Since: August 6, 2011 Posts: 4 Comments: 37103
RTSplayer u right about the shear in the carribean! check the forecast for the next couple of days. WOW!
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Models are really starting to like 99l now.

Also, Caribbean wave has more convection than ever before. Still not taking anyone's notice though. The shear has come down a lot in the vicinity.
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Do the system near NC dissipate?
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check out this wave behind 99L. wouldnt be suprised to see something on this later on or by aug 1st
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1639. bappit
Quoting aspectre:

So why no ATCF for 31July2012?

See the about page for that product.

"Currently, this product combines information from five data sources to create a mid-level (near 700 hPa) wind analysis using a variational approach described in Knaff and DeMaria (2006). The resulting mid-level winds are then adjusted to the surface applying a very simple single column approach. Over the ocean an adjustment factor is applied, which is a function of radius from the center ranging from 0.9 to 0.7, and the winds are turned 20 degrees toward low pressure. Over land, the oceanic winds are reduced by an additional 20% and turned an additional 20 degrees toward low pressure."

So it assumes that the mid-level circulation that it analyzes from the data is actually present at the surface. That is not necessarily true. Also, the analysis it performs on the data may itself be off.
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99L
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99L
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99L should be at 40% by the next TWO
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Quoting AtHomeInTX:


Hey Wes. I don't know how many are still awake now lol. But 99l looks to be holding its own on satellite. :)

I see that the core of 99L seems to be organizing a little bit better this morning. But what concerns me is dat shear in the carribean. It may tear this thing up in the next few days
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So why no ATCF for 31July6amGMT?
Member Since: August 21, 2007 Posts: 0 Comments: 4860
i remember when i last was on when debby arrived but now i see this map lite up with colors! folks welcome to the real official start of hurricane season!
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Hey, AtHome... I'm getting ready to leave in a few, but wanted to take a look at 99L before I go. Today may be a big one for 99L. It'll definitely be a hectic one for me...

I'm off...
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Quoting bappit:

That map can be misleading. It is based on a model that assumes a well defined circulation exists.


Alright, where is Ascat then?
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1630. bappit
Quoting GTcooliebai:
The circulation is becoming better defined:






That map can be misleading. It is based on a model that assumes a well defined circulation exists.
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Quoting AtHomeInTX:


Hey Wes. I don't know how many are still awake now lol. But 99l looks to be holding its own on satellite. :)



I'm always awake on nights like these.
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Link

You sure can see some shear in the W Atlantic/Caribbean on satellite. That ULL to the N of 99L can't seem to make up it's mind what it wants to do.
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Quoting GTcooliebai:
Euro 144 hrs. out:



GFS 144 hrs. out:



Euro is faster than the GFS, but both heading in a general westward path.


What's that stuff in Floriduh?
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I'm out for the night, Goodnight everyone.
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Quoting bigwes6844:
good morning/night everybody! havent been on in a few! been working late nights. but i see 99L is finally waking evryone up


Hey Wes. I don't know how many are still awake now lol. But 99l looks to be holding its own on satellite. :)

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It's hard to say....but I have a lot of confidence in the GFS right now. It might turn out all the models will be wrong lol 99L is taking it's sweet time out there...so the GFS is probably real close to the speed timing(OOZ run). The ECMWF looks like it might be too fast imo
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The circulation is becoming better defined:





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good morning/night everybody! havent been on in a few! been working late nights. but i see 99L is finally waking evryone up
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Quoting robert88:
I'm thinking SA or Yucatan...if it can even survive. One thing is for sure the GFS and ECMWF are not too excited about this system. The ECMWF does have a lot to prove after the last disaster. Going by atmospheric conditions in the Caribbean you would think that anything taking that route is doomed.


I was surprised that it held onto anything enough to make it to the gulf in the last EURO run. Previous runs had it weak through the Caribbean. Which is basically what the GFS showed. The CMC is still showing a stronger system reaching Florida's east coast. Guess we'll see how the models perform this go round.
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Quoting robert88:
I'm thinking SA or Yucatan...if it can even survive. One thing is for sure the GFS and ECMWF are not too excited about this system. The ECMWF does have a lot to prove after the last disaster. Going by atmospheric conditions in the Caribbean you would think that anything taking that route is doomed.
I doubt South America, anything from the Mosquito Coast northward, like you said though if it can make it out of the Caribbean alive. Best atmospheric conditions would be north of the islands, which is why the CMC seems the most bullish in terms of strength.
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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.