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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1671. nigel20
Quoting ProgressivePulse:


Vigorous tropical wave heading into the SW Atl, always gotta keep an eye on em. May be able to sneak into a little sweet spot last minute.


Hey PP! How have you been?
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Quoting kmanislander:


TD or minimal TS IMO. A lot would have to happen in the next 15 degrees of longitude to change that.


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Quoting JLPR2:


Pretty much the same that fell in the Airport, I'm a little over a mile from it.


I was in a brief power outage in Santurce when a heavy thunderstorm moved thru around noon.
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It is still early in the season to expect a dynamic CV system. Upper level conditions are still not optimal so I see this as a weaker system passing through the Southern Caribbean initially. If and when it gets to 75W things may change significantly.


A CV system is usually present or forming in the latter part of august/early Sept.
But, not unheard of to happen outside those perimeters.
The low lat. of 99l has the look of going thru the Caribbean at present time, and may be a factor in the GOM down the line. If 99l gets thru the Caribbean and maintains tropical strength, it bears watching from Mexico up to the Gulf states (NW Fla to South Texas)
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Quoting Huracaneer:
One thing I don't understand ... If the Dominican Republic blob has 0% chance, why does the NHC keep talking about it?


Vigorous tropical wave heading into the SW Atl, always gotta keep an eye on em. May be able to sneak into a little sweet spot last minute.

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I believe 99L has a decent chance at development....that said it needs to detach from the ITCZ, and develop a well defined CDO!! A west-northwestward component is becoming evident on satellite imagery. If 99L can develop into a TS before it reaches the area south of the Dominican Republic i believe it stands a chance at surviving the harsher trade winds of the western Carribean. Thereafter a stronger storm would most likely enter the GOM, while a weaker system or open wave would go into the Yucatin or SA!! JMO
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Quoting DDR:

Thanks for your input Kman its always welcomed.


Just an estimate, mind you. Follow your local weather forecasting authorities :-)
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1663. JLPR2
Quoting Tropicsweatherpr:
JLPR2, how much rain you got in Carolina today?


Pretty much the same that fell in the Airport, I'm a little over a mile from it.
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Quoting TropicalAnalystwx13:

15 degrees of longitude is about 4 days worth.


More like 2.5 days at 15 MPH
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1661. Grothar
Quoting Huracaneer:
One thing I don't understand ... If the Dominican Republic blob has 0% chance, why does the NHC keep talking about it?


It is still expected to bring a lot of rain and squally weather to the Bahamas and Florida in a few days.
Member Since: July 17, 2009 Posts: 69 Comments: 25366
First time since I've started making these that I've given a red circle.

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Did they run the 12Z GFDL? I only see the 06Z at the FSU site (although they got the 18Z hwrf).
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Quoting Huracaneer:


LOL! However, I suspect that maybe it's because it has some tropical mass characteristics (lot's of rain), but very little chance of becoming a storm? I'm just trying to figure out the minds at the NHC.


haha..when you figure them out let me know :)
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1657. nigel20
Quoting DDR:

Thats right on top of me,but the question is how strong will it be?

Hey DDR! Which was the last storm to affect Trinidad?
I know you guys are generally spared most of the effects of tropical storms and hurricanes.
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when DMAX kicks in 99L should explode with convection like a nuke
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1653. DDR
Quoting kmanislander:


TD or minimal TS IMO. A lot would have to happen in the next 15 degrees of longitude to change that.

Thanks for your input Kman its always welcomed.
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Quoting muddertracker:


They've been as bored as all of us!


LOL! However, I suspect that maybe it's because it has some tropical mass characteristics (lot's of rain), but very little chance of becoming a storm? I'm just trying to figure out the minds at the NHC.
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Quoting kmanislander:


TD or minimal TS IMO. A lot would have to happen in the next 15 degrees of longitude to change that.

15 degrees of longitude is about 3-4 days worth.
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JLPR2, how much rain you got in Carolina today?
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Quoting TropicalAnalystwx13:

HWFI.



Cool. Me too.
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Quoting KoritheMan:


I wouldn't expect a track into Honduras. The system would have to remain quite weak.
Thank God for now I don`t want any rain I am going to the beach this week and next and I want to have fun.I am going back to classes the 15 of August.
Member Since: October 15, 2011 Posts: 0 Comments: 4005
Quoting Huracaneer:
One thing I don't understand ... If the Dominican Republic blob has 0% chance, why does the NHC keep talking about it?


They've been as bored as all of us!
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Quoting KoritheMan:


What are your thoughts on the path?

HWFI.

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Quoting DDR:

Thats right on top of me,but the question is how strong will it be?


TD or minimal TS IMO. A lot would have to happen in the next 15 degrees of longitude to change that.
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Quoting TropicalAnalystwx13:
Leeward Islands should be preparing for a strong tropical storm.

So now SHIPS forecasts a hurricane again, and yes they should prepare for a strong TS.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
1642. JLPR2
Looks like OSCAT will miss 99L, but it did catch the low around the CV islands.



Would dare to say it is better defined than 99L's.

XD
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Quoting Tropicsweatherpr:


The Windwards.

Yeah, those.
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One thing I don't understand ... If the Dominican Republic blob has 0% chance, why does the NHC keep talking about it?
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1624. RadarRich 2:55 AM GMT on August 01, 2012

A fun storm to watch as time goes by. Hopefully, no destructive implications down the line.


edit: "Interesting" storm to watch
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Quoting TropicalAnalystwx13:
Leeward Islands should be preparing for a strong tropical storm.



What are your thoughts on the path?
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Quoting TropicalAnalystwx13:
Leeward Islands should be preparing for a strong tropical storm.



The Windwards.
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Quoting RadarRich:

1606. kmanislander 2:43 AM GMT on August 01, 2012LOL. The thing is that 99L is in a steady state at the moment. Still too early for whatever Dmax may bring and the system needs to pull up to at least 11 N to avoid running into SA. I do believe that it will enter the Caribbean near 11/12 N and just skirt along the N coast of SA.

The main thing I am watching for now is a bit of a blow up overnight followed by a solid CDO developing near 55W. My best guess is classification as a TD close to 60W

JUST MY OPINION
99L is just at that lat. which will determine its eventual track. It is showing development on its own just a tad north outside the convergence zone. Any strengthening in the next day or so, will absolutely affect the path, as we all know. The stronger the cyclone, the more poleward bias. It has the look of a Caribbean track at present, since it is just south of 10, but that can change with the intensity factor. All said and done, very impressive circulation at present time. A fun storm to watch as time goes by. Hopefully, no destructive implications down the line.


It is still early in the season to expect a dynamic CV system. Upper level conditions are still not optimal so I see this as a weaker system passing through the Southern Caribbean initially. If and when it gets to 75W things may change significantly.
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The Windward Islands should be preparing for a strong tropical storm.

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1634. JLPR2
Quoting KoritheMan:


Ignorance is bliss, my friend.


Reality, it's better to know than be ignorant. :)

99L seems pretty disorganized still. It needs to break off the ITCZ to see if it can finally organize itself a nice LLC.

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1633. nigel20
Quoting Tropicsweatherpr:
Good evening nigel. It was a rainy day in PR as the tail of wave moved thru..

CLIMATE...A RECORD RAINFALL OF 1.56 INCHES WAS SET AT THE SAN JUAN
LUIS MUNOZ MARIN INTERNATIONAL AIRPORT TODAY. THIS BROKE THE OLD
RECORD OF 1.12 SET IN 1957.

Hey Tropics! That record was there for a pretty long time.
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Quoting allancalderini:
anyone think there is a chance it pass near me Because a landfall as I am seeing is almost impossible but could it bring me a little of rain or it is going to pass north of me? what are your thoughts people?I live in Honduras by the ones that don`t know where I live.


I wouldn't expect a track into Honduras. The system would have to remain quite weak.
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Quoting nigel20:

Hey Kman! Maybe we'll get some rain from the tropical wave over Hispaniola...we need to watch 99L very keenly as well.


Not as much rain as we thought though. That wave is easing off to the WNW, may pass us by except for the odd shower.
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1630. DDR
Quoting kmanislander:


Should be at 10N by early in the morning. Expect 11 or 12N by 60W.

Thats right on top of me,but the question is how strong will it be?
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My prediction on AL99
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Good evening nigel. It was a rainy day in PR as the tail of wave moved thru..

CLIMATE...A RECORD RAINFALL OF 1.56 INCHES WAS SET AT THE SAN JUAN
LUIS MUNOZ MARIN INTERNATIONAL AIRPORT TODAY. THIS BROKE THE OLD
RECORD OF 1.12 SET IN 1957.
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Quoting JLPR2:


ASCAT always disappoints me, was expecting a nicer LLC but it hasn't improved that much.


Ignorance is bliss, my friend.
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anyone think there is a chance it pass near me Because a landfall as I am seeing is almost impossible but could it bring me a little of rain or it is going to pass north of me? what are your thoughts people?I live in Honduras by the ones that don`t know where I live.
Member Since: October 15, 2011 Posts: 0 Comments: 4005
Cool Past Weather Pic!!!
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1606. kmanislander 2:43 AM GMT on August 01, 2012LOL. The thing is that 99L is in a steady state at the moment. Still too early for whatever Dmax may bring and the system needs to pull up to at least 11 N to avoid running into SA. I do believe that it will enter the Caribbean near 11/12 N and just skirt along the N coast of SA.

The main thing I am watching for now is a bit of a blow up overnight followed by a solid CDO developing near 55W. My best guess is classification as a TD close to 60W

JUST MY OPINION
99L is just at that lat. which will determine its eventual track. It is showing development on its own just a tad north outside the convergence zone. Any strengthening in the next day or so, will absolutely affect the path, as we all know. The stronger the cyclone, the more poleward bias. It has the look of a Caribbean track at present, since it is just south of 10, but that can change with the intensity factor. All said and done, very impressive circulation at present time. A fun storm to watch as time goes by. Hopefully, no destructive implications down the line.
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1623. nigel20
Quoting kmanislander:


Could be, but shear is very near to the Northern edge of the circulation and may disrupt it for a while. Earlier today I thought that it would close off within 12 to 18 hours but it looks a little ragged tonight.It is now closing in on 45W and appears to have picked up some forward speed.

Hey Kman! Maybe we'll get some rain from the tropical wave over Hispaniola...we need to watch 99L very keenly as well.
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1622. JLPR2
Quoting KoritheMan:


Still no latitude though. Gonna have to lift northward if it wants to survive.


Seems to be at 10.5N already.

ASCAT always disappoints me, was expecting a nicer LLC but it hasn't improved that much.
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Not so well, as wxchaser97 did

Note: If Ernesto can reach hurricane cat.1, the Cone will shift more to the north,since GfS are predicting weak storm,and make a disagreement with the ships, icon and others intensity models
Member Since: June 20, 2012 Posts: 0 Comments: 2150

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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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