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 Huracaneer:


There is still a lot of good people in this blog, Levi for one and (knock on wood) the trolls haven't been too horrible lately (although he whose name should not be mentioned but think shower curtains) paid us a visit lately. Yeah it took me a while to feel like a could post without making a total fool of myself (now just a partial fool). By the way for anybody out there, is the MJO considered a Kelvin wave?


Yep...great bloggers here. Over the years there has been drama and trolls..but WU is still the best!
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Quoting Gearsts:
Warming clouds tops...


And very ragged. A work in progress
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Quoting nigel20:
99L


Plenty of moisture there,but the sal is not far away to the north.
Member Since: April 29, 2009 Posts: 75 Comments: 14310
1718. Gearsts
Warming clouds tops...
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1717. 19N81W
So if it does come into the wcarib we are looking at 6 to 7 days for cayman? If....
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1716. nigel20
99L
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Quoting muddertracker:


Yeah..I found this site in 2005 (like a lot of people) and the blog was so different then. Much more technical..it took me a long time to learn enough to feel able to even join. Drakoen, weather456, etc., were amazing..they answered questions and "taught." Different now, but I still love it. I agree...TD tomorrow night if it can gain some latitude. I'm waiting for it to develop an LLC before I put much trust in the model tracks.


There is still a lot of good people in this blog, Levi for one and (knock on wood) the trolls haven't been too horrible lately (although he whose name should not be mentioned but think shower curtains) paid us a visit lately. Yeah it took me a while to feel like a could post without making a total fool of myself (now just a partial fool). By the way for anybody out there, is the MJO considered a Kelvin wave?
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Going to go write a blog on 99L, back in a little bit.
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We need a TD first before worrying about wind speeds down the road.
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Quoting wunderkidcayman:

yes you are right I do not believe we will see a 60mph storm at 60W we will have a 70mph or maybe even a 75mph
60-65mph imo
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Quoting wunderkidcayman:

yes you are right I do not believe we will see a 60mph storm at 60W we will have a 70mph or maybe even a 75mph


Duly noted.
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1710. Grothar
With this image you can see where 99L has moved since its last position and the dry air.

Member Since: July 17, 2009 Posts: 71 Comments: 26426
Quoting kmanislander:


I corrected my post to knots which converts to about 52 MPH. I am not saying they should not prepare, everyone should. But I do not believe we will see a 60 MPH storm at 60W. Just my view. Could be wrong.

yes you are right I do not believe we will see a 60mph storm at 60W we will have a 70mph or maybe even a 75mph
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Quoting wunderkidcayman:

close to how I have mine
where you have your 65mph at 120h I have it as 75mph and at 144h I have mine at 80mph and at 168h I have it at 90mph
I'm waiting to see what happens when it hits the Windward Islands to make any intensity changes that far out.
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1673. KoritheMan 3:13 AM GMT on August 01, 2012

99L wouldn't be a Cape Verde storm.



No argument there. It is all in the definition.
A tropical system is a tropical system no matter which way you slice it. I wonder if 99L gets its act together sooner than later, (becoming stronger) and tries to move more nnwestward and goes above the islands(PR, DOM, etc) Then the East coast of the CONUS needs to be observant of possible landfall. Tricky stuff, and timing is obviously crucial
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1706. Gearsts
Quoting wxchaser97:
Ugly looking lol
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Saola is getting ready to explode toward strong typhoon.
Member Since: August 1, 2011 Posts: 28 Comments: 8027
Quoting TropicalAnalystwx13:

It's at 60 mph. Regardless, the Windward Islands need to be preparing for tropical storm conditions.


I corrected my post to knots which converts to about 52 MPH. I am not saying they should not prepare, everyone should. But I do not believe we will see a 60 MPH storm at 60W. Just my view. Could be wrong.
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Quoting ProgressivePulse:


There is a COL area between the ridge in the Gulf and the ATL ridge. Notice the area of light shear in the SW Bahamas?



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.
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Quoting wxchaser97:
I know, its hard to completely do that without messing up the map and it is past 11pm.
Haha, I was just playing with ya :) That's why I uses Paint.NET program so I can have couple of layers.
Member Since: August 1, 2011 Posts: 28 Comments: 8027
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Quoting Huracaneer:


Just noticed that you joined the blog within a few days of the the time I did. Although I had been lurking off and on since 2004 (that season made a lot of Florida converts). But have been going to wunderground since 1995, telnet, even before graphical browsers. I think 99L is going to develop into a TD in the next 24 hours, unless it fails to gain some latitude.


Yeah..I found this site in 2005 (like a lot of people) and the blog was so different then. Much more technical..it took me a long time to learn enough to feel able to even join. Drakoen, weather456, etc., were amazing..they answered questions and "taught." Different now, but I still love it. I agree...TD tomorrow night if it can gain some latitude. I'm waiting for it to develop an LLC before I put much trust in the model tracks.
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Quoting wxchaser97:
Revised track after further analysis/forecasting and for those who didn't see it, my forecast graphic on 99L. The track moved farther north for those who didn't know.

close to how I have mine
where you have your 65mph at 120h I have it as 75mph and at 144h I have mine at 80mph and at 168h I have it at 90mph
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1698. nigel20
Saola

Saola Short Floater - Rainbow Color Imagery Loop
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Quoting kmanislander:


LGEM at 45 MPH at 60 hrs if I read that right. Minimal IMO.

It's at 60 mph. Regardless, the Windward Islands need to be preparing for tropical storm conditions.
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Quoting Bluestorm5:
You didn't erases all of the old line ;)
I know, its hard to completely do that without messing up the map and it is past 11pm.
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Quoting sunlinepr:
Let's just pray it doesn't pull a Typhoon Vicente...
Member Since: August 1, 2011 Posts: 28 Comments: 8027
1693. JLPR2
Quoting wunderkidcayman:
wow 99L starting to pop convection new sat image just came out (02:45 UTC) looking at AVN red spot just formed 10.3N 44.7W lets see if it continues


Pretty much where ascat shows some form of circulation.

It can only get more interesting from here on out.
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Quoting TropicalAnalystwx13:

The reliable LGEM model says different.



LGEM at 45 knots at 60 hrs if I read that right. Minimal IMO.
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99L is exactly 1,257 miles west-southwest of one of the Windward Islands. Moving at 15 mph (which is likely a little fast), it would take 99L 3 and a half days to reach the Islands.
Member Since: July 6, 2010 Posts: 113 Comments: 32255
Quoting Huracaneer:


Not according to that shear map you just posted!


There is a COL area between the ridge in the Gulf and the ATL ridge. Notice the area of light shear in the SW Bahamas?

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1689. nigel20
Quoting sunlinepr:

Saola is looking better frame after frame.
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Quoting wxchaser97:
Revised track after further analysis/forecasting and for those who didn't see it, my forecast graphic on 99L. The track moved farther north for those who didn't know.
You didn't erases all of the old line ;)
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Quoting kmanislander:


At 60 Hrs only one model showing more than a bare minimal TS

The reliable LGEM model says different.

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1686. nigel20
Quoting ProgressivePulse:


Crazy busy but well, thank you. How about yourself?

I've been good as well.
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Quoting ProgressivePulse:




Thanks! I guess they did not update the FSU site. That run doesn't do much with 99L.
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wow 99L starting to pop convection new sat image just came out (02:45 UTC) looking at AVN red spot just formed 10.3N 44.7W lets see if it continues
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There is 40 knot shear to the north and 30 knot shear to the west of 99L:



Lower convergence:



Upper divergence:



850mb. vort:

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Quoting sunlinepr:




At 60 Hrs only one model showing more than a bare minimal TS
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Quoting Grothar:


It is still expected to bring a lot of rain and squally weather to the Bahamas and Florida in a few days.


Yes, I think you are right, should be the recipient of some of that by this weekend.
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1679. JLPR2
Quoting Tropicsweatherpr:


I was in a brief power outage in Santurce when a heavy thunderstorm moved thru around noon.


I'm happy to say power never went out in my house.
Huzzah! XD
Wait for it, I will probably loose power on a sunny day.
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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.
Read more at http://www.wunderground.com/tropical/AXNT20.html#A Muj8DlcFrG3u16d.99

Speed is 11.5 to 17 MPH
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Quoting nigel20:

Hey PP! How have you been?


Crazy busy but well, thank you. How about yourself?
Member Since: August 19, 2005 Posts: 5 Comments: 5449
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.



Not according to that shear map you just posted!
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Revised track after further analysis/forecasting and for those who didn't see it, my forecast graphic on 99L. The track moved farther north for those who didn't know.
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Quoting muddertracker:


haha..when you figure them out let me know :)


Just noticed that you joined the blog within a few days of the the time I did. Although I had been lurking off and on since 2004 (that season made a lot of Florida converts). But have been going to wunderground since 1995, telnet, even before graphical browsers. I think 99L is going to develop into a TD in the next 24 hours, unless it fails to gain some latitude.
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Quoting RadarRich:
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)


99L wouldn't be a Cape Verde storm.
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Quoting Huracaneer:
Did they run the 12Z GFDL? I only see the 06Z at the FSU site (although they got the 18Z hwrf).


Member Since: August 19, 2005 Posts: 5 Comments: 5449
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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.