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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Afternoon everyone.

Chance of severe weather again today, so running the mobile webcam all afternoon.
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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.

Hot rain falls on Saudi Arabia
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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.


That is mind numbing heat...WOW!
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Quoting MAweatherboy1:
Another ensemble member... The thing on the Yucatan is 99L:

that think is really near me hope it doesn`t materialize.
Member Since: October 15, 2011 Posts: 0 Comments: 4467
With shear being low, center relocations should be very few..
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Quoting MAweatherboy1:

Hey Nigel. Definitely could... I'm guessing you guys need the rain.

Yeah, though not as much as earlier this month.
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Quoting MississippiWx:


I stand corrected. Yikes...
..no wonder they wear the protective robes and all that
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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 stand corrected. Yikes...
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Quoting RussianWinter:


Whoa there, what happened to the shear that's supposed to save us all from the big storm? 0.0


Still three-four days away.
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Quoting OracleDeAtlantis:
After watching Levi's forecast yesterday, I don't think he was counting on this ...

Clearly, this wave south of PR has increasing chances with every click of the shear tendency forecast.

What's to keep it from strengthening at this point, somebody please tell me? It's already stacked vertically and the water down there is almost boiling.

It's time to wake up Mother Nature. It's time to roll.







It's way too large. The wave axis is too long and the associated inverted-V structure is too broad to consolidate into a low pressure center in any reasonable amount of time, and the surface winds north of the Bahamas are out of the south now as that frontal boundary lies along the SE US coast, which means surface convergence is about to be taken away from the wave except for the trade winds coming into it from the east.
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Latest model runs shifted noticeably south...ensembles still all over the place...


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Quoting nigel20:

Hey MA! 99L could pass very close to Jamaica.

Hey Nigel. Definitely could... I'm guessing you guys need the rain.
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Quoting MississippiWx:


I think that reading would be physically impossible on earth. Lol. A 110 degree temp with an 87 degree dew point. Not happening...
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.
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Quoting nigel20:
48Hr shear forecast


Whoa there, what happened to the shear that's supposed to save us all from the big storm? 0.0
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Quoting nigel20:
48Hr shear forecast


132 hours out (GFS). Doesn't look pretty down the road for 99L if it stays in Caribbean, but things change.

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99l.in.the.nw.carib....seems.more.likely
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Quoting Grothar:
Coming into full view. Plenty of moisture ahead.



Nice job predicting the convection in the NW quad.

These dots are Tropical Overshooting Tops, which represent developing/strong convection.

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Steering: 99L heading straight for the Caribbean.




Morphed Integrated Microwave Imagery at CIMSS - Total Precipitable Water (MIMIC-TPW)

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Quoting Grothar:
Coming into full view. Plenty of moisture ahead.



I bet this is a hurricane before reaching the islands. Once it departs from the ITCZ expect this to go straight Ernesto.
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Quoting MAweatherboy1:
Another ensemble member... The thing on the Yucatan is 99L:


Hey MA! 99L could pass very close to Jamaica.
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Quoting OracleDeAtlantis:
After watching Levi's forecast yesterday, I don't think he was counting on this ...

Clearly, this wave south of PR has increasing chances with every click of the shear tendency forecast.

What's to keep it from strengthening at this point, somebody please tell me? It's already stacked vertically and the water down there is almost boiling.

It's time to wake up Mother Nature. It's time to roll.





..it sure is looking better
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Quoting RitaEvac:


Blue track looks pretty good
Thanks, I now think 99L will go somewhere in the Caribbean.
Member Since: March 16, 2012 Posts: 127 Comments: 7972
845. VR46L
Quoting wunderkidcayman:
well guys looks like 99L will go into Caribbean I was right once again

oh anyone see the 24-72h forecast map from NHC has low #2 by 72


Where do you think it will go after it gets to the Caribbean ?
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Quoting RitaEvac:
You'd be dead if this was legit, but it's not

W SIDE OF WOODWARD, WOODWARD, Oklahoma (PWS)
Clear
110 °F
Clear
Humidity: 50%
Dew Point: 87 °F
Wind: 0.0 mph from the ESE
Wind Gust: 3.0 mph
Pressure: 28.10 in (Rising)
Heat Index: 150 °F


CSB...I used to run the "gun" for a 2-man land surveying crew. On a 108 degree day, where a popcorn shower hit the gully we were in on Lake Travis (Austin, TX), with no wind at all and a soon-after blazing sun, my $50K laser read a 147 degree heat index (100% accurate). I drank 2.5 gallons of water that day, and it all came out via sweat.
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After watching Levi's forecast yesterday, I don't think he was counting on this ...

Clearly, this wave south of PR has increasing chances with every click of the shear tendency forecast.

What's to keep it from strengthening at this point, somebody please tell me? It's already stacked vertically and the water down there is almost boiling.

It's time to wake up Mother Nature. It's time to roll.





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Quoting Pocamocca:

August 8/16. MA - Why do you keep showing this stuff??

Let's at least get through JULY!!!

Only a few hours to go then... I show this stuff because that's kind of what we do here.

Quoting Tropicsweatherpr:


That one is homebrown in BOC right?

Classic homegrown system, yep.
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48Hr shear forecast
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Quoting Grothar:
Coming into full view. Plenty of moisture ahead.

It is starting to look like September out there.
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.........................Oklahoma heat index
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Another ensemble member... The thing on the Yucatan is 99L:

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Quoting MAweatherboy1:
This is one of the 12z GFS ensemble members... The storm in the Gulf is NOT related to 99L:



Don't throw that possibility out either because look what the operational has later on:



That one is homegrown in BOC right?
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Quoting MississippiWx:


Not sure many people ever doubted it going into the Caribbean...


Fingers crossed, it'll turn more wnw ofter 50W. I guess..
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This is one of the 12z GFS ensemble members... The storm in the Gulf is NOT related to 99L:



Don't throw that possibility out either because look what the operational has later on:

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BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE BLACKSBURG VA
336 PM EDT TUE JUL 31 2012

THE NATIONAL WEATHER SERVICE IN BLACKSBURG HAS ISSUED A

* FLASH FLOOD WARNING FOR...
WESTERN TAZEWELL COUNTY IN SOUTHWEST VIRGINIA

* UNTIL 930 PM EDT.

* AT 329 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
VERY HEAVY RAIN FROM A THUNDERSTORM OVER THE WARNED AREA.

* LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO JEWELL
RIDGE...GLEN BURKE...BANDY...RICHLANDS AND AMONATE. WATCH FOR
FLOODING ALONG MUDLICK CREEK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF SMALL
CREEKS AND STREAMS...COUNTRY ROADS...AS WELL AS FARMLAND ALONG THE
BANKS OF CREEKS AND STREAMS.

PLEASE RELAY ANY REPORTS OF FLOODING INCLUDING MUDSLIDES...OR ROAD
CLOSURES TO THE NATIONAL WEATHER SERVICE IN BLACKSBURG BY CALLING
TOLL FREE...1...8 6 6...2 1 5...4 3 2 4. DELAYED REPORTS ARE WELCOME.



LAT...LON 3715 8188 3718 8187 3719 8179 3722 8176
3721 8156 3723 8152 3697 8161 3696 8170
3698 8172 3696 8178 3705 8183 3710 8189
3715 8191



KK
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72Hr forecast
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Quoting wunderkidcayman:
well guys looks like 99L will go into Caribbean I was right once again

oh anyone see the 24-72h forecast map from NHC has low #2 by 72


Not sure many people ever doubted it going into the Caribbean...
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Quoting Grothar:
My post from an hour ago.

Expect convection to start building in the NW quadrant. If a strong low forms, it may be farther to the North than has been intialized.








Interesting.. i might cancel my flight to the Windwards ^^
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Coming into full view. Plenty of moisture ahead.

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Quoting wunderkidcayman:
well guys looks like 99L will go into Caribbean I was right once again

oh anyone see the 24-72h forecast map from NHC has low #2 by 72


What happens when you are wrong though. =(.

Even the NHC was wrong with ol Debby.
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Quoting JLPR2:


Wasn't that the same thing that made Tropical Storm Maria explode with convection when it was east of the islands last year?



Judging by the upper level cirus in that shot, I doubt it. Then again, I dont have an archive of the CCKW that goes back that far.

Looks to be enhanced convection due to interaction with a strong ULL or TUTT.

If anyone has an archive of the last 7-10 days of the EPAC, then you will be able to see how convection was enhanced in that region while the wave passed over.
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Invest 99L Funktop:

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Quoting Tropicsweatherpr:


You have to watch there 99L as down the road it may track close to that island but intensity is uncertain.

Agreed.
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well guys looks like 99L will go into Caribbean I was right once again

oh anyone see the 24-72h forecast map from NHC has low #2 by 72
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821. JLPR2
Quoting MississippiWx:


I think you're referring to the TUTT circulation.


Ah, I see, thought I had heard that term last year.
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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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