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 SFLWeatherman:
Q. ok so what wiil 99L be at 8PM
A. 30%
B. 40%
C. 50%
D. 60%
E. 70%
F. 80%
Q. what time will 99L be a TD or TS
A. 11PM
B. 5AM
C. 11AM
D. 5PM

D. and 5Pm. Tomorrow.
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1020. nigel20
Quoting TropicalAnalystwx13:
Good afternoon guys.

If I worked at the National Hurricane Center I would give 99L a 60% chance of formation at the 8PM EDT TWO.

Good afternoon TA!
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TPW loops would make one think that the center is slightly north of 10N. Also, it's fairly obvious that the ITCZ separation is underway.

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Quoting SFLWeatherman:
Q. ok so what wiil 99L be at 8PM
A. 30%
B. 40%
C. 50%
D. 60%
E. 70%
F. 80%
Q. what time will 99L be a TD or TS
A. 11PM
B. 5AM
C. 11AM
D. 5PM
G. 90% and C. 11 am
Member Since: August 31, 2009 Posts: 0 Comments: 5628


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1016. 900MB
Quoting StormTracker2K:



NHC must be scratching their heads right now as this looks to be no doubt be a TD if not Ernesto as we speak.




It does look pretty well put together. Just moving into warmer waters, it could intensify far sooner than thought.
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1015. pcola57
Quoting KEEPEROFTHEGATE:



i can post what i like here bud
and it the latest info from navy
if a TCFA is to show up
it will be there first



TCFA always shows at the Navy site first as Keeper says..

Quoting Minnemike:
i don't know how to post the visual of this loop, but go here Link to see how the moisture field is really tightening in on 99L in last few frames.. the invest is definitely consolidating now, but at it's own detriment perhaps.
an airmass to the south, as Levi stated, looks to be a significant swath of dry air.


JMO for what it's worth..
Those are morphed composite scans ..pretty darn accurate If you ask me..however these types of T Waves over the open water can induce their own enviroments and todays displayed loop can change dramatically from day to day..
This is only my personal observation and opinion and in no way do I dis-agree or even agree with you Minnemike.. :)
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Quoting wunderkidcayman:

yep quite right
so kman how are you


Pretty good right now. Just watching to see if 99L will skirt the area near Trinidad which it looks like it will do. Perhaps 11/12 N when it enters the Caribbean which means little to no further development until about 75W due to dry air entrainment from SA if it stays close to the coast line.

A lot depends on how well it organises before entering the Caribbean and the signs today suggest it might be much stronger by then than suggested by current model runs.
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1013. LargoFl
Quoting Patrap:
............pat do you think this might develop?
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Good afternoon guys.

If I worked at the National Hurricane Center I would give 99L a 60% chance of formation at the 8PM EDT TWO. It has definitely come together today and is in the process of separating from the Intertropical Convergence Zone.
Member Since: July 6, 2010 Posts: 112 Comments: 31326
Good Afternoon to everyone!

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I'd give 99L a 60% chance of developing into a tropical cyclone over the next 48 hours. The only thing I find interesting is the two best global models' (GFS and ECMWF) resilience to develop 99L into anything more than an open wave.
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Is CMC talking about a new Hugo?

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Q. ok so what wiil 99L be at 8PM
A. 30%
B. 40%
C. 50%
D. 60%
E. 70%
F. 80%
Q. what time will 99L be a TD or TS
A. 11PM
B. 5AM
C. 11AM
D. 5PM
Member Since: Posts: Comments:
Quoting kmanislander:


It is looking like it could close off within 12 to 18 hours IMO if the rate of organization continues as it has today. 99L has done very well during the heat of the day and Dmin is near out there so I would expect further improvement in the overall presentation this evening and late tonight.
T.D by tomorrow morning in my opinion.All though the NHC may go the conservative route and issue T.D status tomorrow night.
Member Since: August 14, 2010 Posts: 10 Comments: 16327
1004. etxwx
Quoting Neapolitan:
On July 8, 2003, the world record high dewpoint of 95 was recorded at Dhahran, Saudi Arabia. Combined with a temperature of 108, the heat index reached a comfortable 174 degrees.

Sounds like fun...so long as you enjoy spending time in a sauna.

I know it's different but when I read that I couldn't help but think that well done beef is cooked to 160 degrees F.
Yicks!
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1003. 900MB
Quoting MAweatherboy1:
A couple more ensemble members from the 12z GFS:





The general consensus is that if it goes north of the islands then strengthening is likely and it could do one of these scenarios. However if it goes south into the Caribbean, which is more likely, it should stay weak and dissipate. Most likely what path it takes will be determined by how quickly it strengthens... All the models that take it north strengthen it more in the short term.


East Coast Hurricane, no thanks!
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1001. WxLogic
I would go with 30% on the next TWO... with a 40% to 50% by tomorrow AM if 99L was able to sustain/generate convection. Specially if it was able to get away from the ITCZ.
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Quoting kmanislander:


That is not NW, just barely due N of West which is essentially W for the NHC

yep quite right
so kman how are you
Member Since: June 13, 2009 Posts: 2 Comments: 10852
Quoting StormTracker2K:



NHC must be scratching their heads right now as this looks to be no doubt be a TD if not Ernesto as we speak.



Well if the T #s are 1.0 then its definately not ernesto
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A couple more ensemble members from the 12z GFS:





The general consensus is that if it goes north of the islands then strengthening is likely and it could do one of these scenarios. However if it goes south into the Caribbean, which is more likely, it should stay weak and dissipate. Most likely what path it takes will be determined by how quickly it strengthens... All the models that take it north strengthen it more in the short term.
Member Since: February 11, 2012 Posts: 82 Comments: 7566
Quoting kmanislander:


It is looking like it could close off within 12 to 18 hours IMO if the rate of organization continues as it has today. 99L has done very well during the heat of the day and Dmin is near in out there so I would expect further improvement in the overall presentation this evening and late tonight.


Agreed. I don't believe it is closed off yet either as the western/southwestern side of the circulation appears to be lacking/weak as of now.
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Quoting ilovehurricanes13:
that will be 40% at 8pm


Or more.
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The nice little cocoon of moisture that 99L is residing in sure is shrinking as dry air approaches from the north and the south in the MIMIC TPW loop. Going to be a small system, vulnerable to shear or dry air intrusions over its future...

MIMIC TPW

Structually continues to impress, so still think TD, perhaps at 11AM tomorrow.

Have a good evening everyone!
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99L
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Quoting Minnemike:
you know i'm just playing you to build cred around here.. i knew you'd take the bait!!
:P
in actuality, the SAL you posted doesn't look all that offensive to tropical development, but i do think development will be hindered by a lack of widely available precipitable moisture.. if it were closer to that wave west, a lot of factors would change, imo.


Have you ever seen me get mad at anybody? :) Just keep throwing those one liners.
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Exageration mode comments

Looks like it is dissipating / For sure it is going anular


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I love it when i ignore a blogger for 2 reasons.
1. I dont have to see their nonsense anymore.
2. I love it when, at the top of the screen, it says
Your list of ignored users has been succesfully updated!
Yay!
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XX/INV/99L
MARK
9.875N/43.25W


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Quoting MississippiWx:
Fairly impressive. Last frame of visible for the day.




NHC must be scratching their heads right now as this looks to be no doubt be a TD if not Ernesto as we speak.


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Quoting MississippiWx:
Fairly impressive. Last frame of visible for the day.



It is looking like it could close off within 12 to 18 hours IMO if the rate of organization continues as it has today. 99L has done very well during the heat of the day and Dmin is near out there so I would expect further improvement in the overall presentation this evening and late tonight.
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Quoting SFLWeatherman:
it move 45 miles north today!!


Apparently so
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Here's a question, anyone can answer or attempt to do so. In comparison with Ivan, Earl 2K4, Emily 2K5, Tomas, etc... Why is it that with 99L everyone seems so tied up in the ITCZ thing, when these storms all developed in that general region 9.0 - 10.5N? I know there are multiple other factors involved, but it appears that 99L should at least have a decent chance of becoming a named storm in 48 hrs...
BTW, I'm in Barbados, and watching this one closely, and with some level of excitement.
Cariboy, if you book a flight fast, you might be able to catch some of this weather by weekend :-)
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Got a nice storm cell approaching the airport now.
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Quoting CorfidiFan:
poof : you are jason and you were this poofed.


And you are a troll. You were just poofed.
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We could be dealing with T.D 5 tomorrow morning.From there we should see modest intensification into a moderate to strong T.S.People(including you Pottery) should be preparing for heavy rains rough surf and strong winds.After that a track into the caribbean seems likely.It is uncertain in terms of intensity of what will become off 99L.Some models show it becoming a open wave but eventually re-organizing into a weak T.S.Now if conditions are favorable in the caribbean we could be dealing with a much stronger system.
Those TCHP values are high and haven't been touched all year and in some spots water is nearing 90 degrees.
Member Since: August 14, 2010 Posts: 10 Comments: 16327
Quoting sunlinepr:
Finally 3/4 cistern tank full....

.............nice shot there..sure looks good huh
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it move 45 miles north today!!
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99L looks a lot better than yesterday.
At 8PM the NHC should give it at LEAST a 50% chance of developing imo if it keeps the trend up.
By tomorrow, we should have our first TD with a number after it this season.
Considering all the other storms skipped TD status and if the ever were a TD, they had a name.
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Fairly impressive. Last frame of visible for the day.

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Finally 3/4 cistern tank full....

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Quoting wxchaser97:
Yeah now I see, thanks for pointing that out.


Take a look at the shortwave loop

This is one of the best ways to determine where the center is. It shows up quite nicely between the 9 and 10 degree N lat. line. Check the lat/lon box and then zoom in when you run the loop
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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.