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 StormTracker2K:


I know some elite on here will disagree but 99L is taking off right now based on satellite. 99L is destin to take a more northerly track as it does appear to be wrapping up nicely now.

The steering is favorable for southern path...
Member Since: August 1, 2011 Posts: 28 Comments: 7913
Quoting StormTracker2K:


I know some elite on here will disagree but 99L is taking off right now based on satellite. 99L is destin to take a more northerly track as it does appear to be wrapping up nicely now.



They never listen to us, Storm! :):)
Member Since: July 17, 2009 Posts: 69 Comments: 25517
919. JLPR2
Quoting StormTracker2K:


I'm telling people this will be a hurricane before entering the Caribbean so get ready if you live in the Leeward Islands.



Nope, a little farther north and west, Puerto Rico. :P

Even though models keep saying south I'm keeping a close eye on it.
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Afternoon everyone.I see 99L is looking better by the hour.I'm sure if it was attached from the ITCZ it would have probably had a 50% chance.I'm confused as to why which ever path 99L it'll be sheared apart.

Doc says if it goes into the caribbean it has a better chance to survive(and so did stormw).Others say if it goes north of the islands it'll also be sheared apart.Which one is it?.

Interesting to note that a TUTT is suppose to set up in the Bahama's.
Member Since: August 14, 2010 Posts: 10 Comments: 16444
Quoting Levi32:


The post you quoted was referring to the wave ahead of 99L.
really? the one moving through hispanola? i thought it would be the remnants of 99L. thanks for verifying
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Quoting Minnemike:
funny, i was just checking out the CIMSS precipitable loop, and it looks like the moisture field is diminishing around 99L, north/south.. if it starts to gain latitude, it might be ingesting a lot of dry air for a while. i don't really consider myself knowledgeable though.. don't quote me!


I won't :)

Member Since: July 17, 2009 Posts: 69 Comments: 25517
Quoting JLPR2:
Almost D-min for 99L. After that 99L should start to explode and things should get interesting.



I'm telling people this will be a hurricane before entering the Caribbean so get ready if you live in the Leeward Islands.

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Quoting KEEPEROFTHEGATE:
No Active Atlantic Tropical Warnings
July-31-12, 4:00:02 PM | Maritime.CDO@navy.mil (FWC-N CDO)
As of Tue, 31 Jul 2012 20:00:02 GMT



is there a point that you keep on reposting that?
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Are you doing a Tropical Tidbit today???
Quoting Levi32:


The post you quoted was referring to the wave ahead of 99L.
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Quoting wxchaser97:

99L is moving NW, I think a moderate to maybe strong TS is more likely for the islands though.


It should fire on all sides and that will only increase its chances more.


I know some elite on here will disagree but 99L is taking off right now based on satellite. 99L is destin to take a more northerly track as it does appear to be wrapping up nicely now.

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This is why I didn't forecasted so far into the future like going toward SE USA. I did thought the storm was going toward USA, but I knew it was a long way out so I only did up to 120 HR into future from 11:30 pm last night EST.

My forecast from last night:



Right now, 99L is just right on my 24 HR mark with the right wind speeds, BUT the models were shifting south and the pattern is favorable for southern path now rather than northern path. My forecast will shift south tonight slightly.

Member Since: August 1, 2011 Posts: 28 Comments: 7913
Looks like hispanola is going to get drenched.
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Quoting StormTracker2K:


It even has that look to it. I'm goin all in that this will be a hurricane before hitting the leeward islands. I'm usually right on this so we'll see.



Animation below.
Link

Also 99L is pulling more north right now out of the ITCZ
Nothing wrong with going out on a limb, if you are correct the leeward islands would need to prepare.
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high that was over the gulf did it move a way
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Surface low forming on SE coast
Member Since: August 19, 2006 Posts: 13 Comments: 14629
I'm going to a friends/neighbor's house so I will be back later.
Member Since: March 16, 2012 Posts: 127 Comments: 7928
905. JLPR2
Almost D-min for 99L. After that 99L should start to explode and things should get interesting.



Sun is down near 25W.
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.................................IS everyone SURE this is still a cold core system sitting over 86 degree gulf water?
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Quoting Stormchaser2007:


Nice job predicting the convection in the NW quad.

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



Thanks. You just made an old man smile.
Member Since: July 17, 2009 Posts: 69 Comments: 25517
Quoting floridaboy14:
what if the low pressure becomes more consolidated before it reaches the carribean and the ensembles of the GFS show 99L stregnthining once it escapes the eastern carribean. Do you think 99L will be anything at all once it exits the Eastern carribean or will it just die and never regenerate?


The post you quoted was referring to the wave ahead of 99L.
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The sheer tendency is dropping immediately to the West-Northwest of 99L and picks up again around the Tutt cell near 55W so it has a pretty favorable window to further organize over the next 36 hours or so.

Link
Member Since: August 8, 2006 Posts: 0 Comments: 8850
Quoting StormTracker2K:


It even has that look to it. I'm goin all in that this will be a hurricane before hitting the leeward islands. I'm usually right on this so we'll see.



Animation below.
Link

Also 99L is pulling more north right now out of the ITCZ

99L is moving NW, I think a moderate to maybe strong TS is more likely for the islands though.

Quoting muddertracker:


Now we just wait to see if it will get spun around :)

It should fire on all sides and that will only increase its chances more.
Member Since: March 16, 2012 Posts: 127 Comments: 7928
Quoting Levi32:


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.


I agree.
Member Since: July 17, 2009 Posts: 69 Comments: 25517
THIS OUTLOOK IS FOR NORTHEAST FLORIDA...SOUTHEAST GEORGIA AND THE
ADJACENT COASTAL WATERS.

.DAY ONE...THIS AFTERNOON AND TONIGHT...

SCATTERED STRONG TO ISOLATED SEVERE THUNDERSTORMS WILL CONTINUE TO
BE POSSIBLE INTO THE EVENING HOURS...MAINLY ACROSS NORTHEAST
FLORIDA. STORM MOTION IS GENERALLY TOWARDS THE EAST-SOUTHEAST AROUND
15 MPH. A FEW SEVERE STORMS WITH DAMAGING WINDS WILL REMAIN POSSIBLE
INTO THE EVENING HOURS...ALTHOUGH MOST OF THE STRONG ACTIVITY WILL
CONTAIN GUSTY WINDS OF 40 TO 50 MPH...DEADLY LIGHTNING AND LOCALLY
HEAVY RAINFALL.

SCATTERED THUNDERSTORMS MAY REDEVELOP DURING THE OVERNIGHT
HOURS...WITH STRONGER THUNDERSTORMS CAPABLE OF PRODUCING GUSTY
WINDS...FREQUENT LIGHTNING STRIKES...AND LOCALLY HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY...
ANOTHER ROUND OF SCATTERED THUNDERSTORMS ARE FORECAST ON
WEDNESDAY...WITH GREATER COVERAGE OF ACTIVITY EXPECTED OVER
NORTHEAST FLORIDA. STRONGER THUNDERSTORMS WILL BE CAPABLE OF
PRODUCING DAMAGING WIND GUSTS...FREQUENT LIGHTNING STRIKES...AND
LOCALLY HEAVY RAINFALL. EXPECT SCATTERED MAINLY AFTERNOON AND
EVENING THUNDERSTORMS FOR THE REMAINDER OF THIS WEEK THROUGH THE
UPCOMING WEEKEND.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE REQUESTED TO SELF-ACTIVATE IF WATCHES OR WARNINGS ARE
ISSUED FOR THEIR LOCATION.

FOR ADDITIONAL INFORMATION...VISIT THE NATIONAL WEATHER SERVICE
IN JACKSONVILLE WEBSITE ON THE INTERNET AT WEATHER.GOV/JAX.

$$

NELSON/JCH
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Quoting stormchaser19:
Swimming team of USA


You're about to get pummeled.
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#894

Thanx for letting all us waiting to watch tonight Sport.
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Member Since: July 15, 2006 Posts: 169 Comments: 53308
Quoting KEEPEROFTHEGATE:
No Active Atlantic Tropical Warnings
July-31-12, 4:00:02 PM | Maritime.CDO@navy.mil (FWC-N CDO)
As of Tue, 31 Jul 2012 20:00:02 GMT


You think TCFA will be issued tonight?
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Saola
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Quoting hurricanejunky:


That is mind numbing heat...WOW!


More like mind-frying heat.
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Member Since: March 16, 2012 Posts: 127 Comments: 7928
Quoting wxchaser97:
Convection increasing in the NW quadrant just like Grothar said it would.


Now we just wait to see if it will get spun around :)
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Quoting wxchaser97:
Convection increasing in the NW quadrant just like Grothar said it would.


It even has that look to it. I'm going all in that this will be a hurricane before hitting the leeward islands. I'm usually right on this so we'll see.



Animation below.
Link

Also 99L is pulling more north right now out of the ITCZ
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No Active Atlantic Tropical Warnings
July-31-12, 4:00:02 PM | Maritime.CDO@navy.mil (FWC-N CDO)
As of Tue, 31 Jul 2012 20:00:02 GMT
Member Since: July 15, 2006 Posts: 169 Comments: 53308
Quoting Levi32:


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.
what if the low pressure becomes more consolidated before it reaches the carribean and the ensembles of the GFS show 99L stregnthining once it escapes the eastern carribean. Do you think 99L will be anything at all once it exits the Eastern carribean or will it just die and never regenerate?
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Quoting LargoFl:


AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
307 PM AST TUE JUL 31 2012

.SYNOPSIS...SHOWERS AND THUNDERSTORMS ASSOCIATED WITH A TROPICAL
WAVE NOW LOCATED ACROSS THE HISPANIOLA WILL CONTINUE TO PERSIST
ACROSS THE LOCAL ISLANDS THROUGH AT LEAST LATE THIS EVENING.
CONVECTION COVERAGE WILL GRADUALLY DECREASE DURING THE OVERNIGHT
HOURS AS WELL AS TOMORROW.

&&

.DISCUSSION...TROPICAL WAVE AND ITS ASSOCIATED MOISTURE WILL
CONTINUE TO MOVE WEST ACROSS THE NORTHEASTERN CARIBBEAN...LEAVING
PERIODS OF SHOWERS AND THUNDERSTORMS ACROSS THE LOCAL ISLANDS.
WEATHER CONDITIONS ARE EXPECTED TO SLOWLY IMPROVE OVERNIGHT.
HOWEVER...SHOWER AND THUNDERSTORM ACTIVITY STILL INCLUDED IN
THE FORECAST PACKAGE...ESPECIALLY ACROSS THE CARIBBEAN WATERS AND
THE EAST AND SOUTH COASTAL AREAS OF PUERTO RICO DUE TO LINGERING
MOISTURE AND FAVORABLE UPPER LEVEL DYNAMICS.

CONVECTION COVERAGE WILL CONTINUE TO GRADUALLY DECREASE ON WEDNESDAY
AND ESPECIALLY ON THURSDAY AS A DRIER AIR MASS MOVES ACROSS THE
FORECAST AREA. MEANWHILE...AT UPPER LEVELS...RIDGE PATTERN WILL
CONTINUE TO PERSIST ACROSS THE EASTERN CARIBBEAN AS UPPER LEVEL
TROUGH SLOWLY DEVELOPS ACROSS THE CENTRAL ATLANTIC. AFOREMENTIONED
TROUGH IS THEN EXPECTED TO DIG SOUTHWEST...REACHING THE NORTHEAST
CARIBBEAN BY THE END OF THE WEEK. THIS FEATURE MAY DESTABILIZE
SOMEWHAT THE LOCAL ATMOSPHERE...AS A RESULT CONTINUE TO EXPECT
AFTERNOON SHOWERS AND THUNDERSTORMS ACROSS THE WESTERN PORTIONS OF
PUERTO RICO FRIDAY AND SATURDAY. TROPICAL WAVE IS EXPECTED TO
REACH THE EASTERN CARIBBEAN EARLY NEXT WEEK.

&&

.AVIATION...AFTERNOON CONVECTION IS MOVING ACROSS PUERTO RICO FROM
THE EAST SOUTHEAST AND WILL CONTINUE TO PRODUCE MOUNTAIN OBSCURATIONS
AS WELL AS SHRA/TSRA THROUGH AT LEAST 01/02Z. AS A RESULT...BRIEF
MVFR/IFR CONDS MAY OCCUR IN AND AROUND TJSJ...TJPS AND POSSIBLY
TJMZ AND TJBQ. LLVL WINDS WILL REMAIN MAINLY FROM THE SOUTH EAST
AT 10-20 KTS FROM SFC TO 20 KFT. WINDS GUSTS UP TO 30 KTS ARE
POSSIBLE WITH SOME +TSRA. CONDS IMPROVE SLOWLY AFT 01/02Z BUT
ANOTHER BAND OF SHRA/TSRA WILL MOVE THROUGH AFT 01/10Z.

&&

.MARINE...SHOWERS AND THUNDERSTORMS ASSOCIATED WITH A TROPICAL WAVE
NOW LOCATED ACROSS THE HISPANIOLA WILL CONTINUE TO PERSIST ACROSS
THE REGIONAL WATERS THROUGH AT LEST TOMORROW MORNING. SMALL CRAFT
ADVISORY REMAINS IN EFFECT UNTIL MIDNIGHT.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 77 89 79 90 / 70 40 20 20
STT 78 87 80 90 / 60 50 30 20
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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MIAMI FL
359 PM EDT TUE JUL 31 2012

FLZ071>074-312045-
INLAND BROWARD COUNTY FL INLAND MIAMI-DADE COUNTY FL METRO BROWARD
COUNTY FL METROPOLITAN MIAMI DADE FL
359 PM EDT TUE JUL 31 2012

THE NATIONAL WEATHER SERVICE IN MIAMI HAS ISSUED A

* SIGNIFICANT WEATHER ADVISORY FOR...
SOUTH CENTRAL BROWARD COUNTY
NORTH CENTRAL MIAMI-DADE COUNTY

* UNTIL 445 PM EDT

* AT 356 PM EDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
STRONG THUNDERSTORM NEAR KENDALE LAKES...AND MOVING NORTH AT 10
MPH.

* THE STORM WILL AFFECT...
SWEETWATER...
MICCOSUKEE RESORT...
MIAMI SPRINGS...
DORAL...
HIALEAH...
MEDLEY...
AND SURROUNDING COMMUNITIES.

FREQUENT TO EXCESSIVE LIGHTNING...GUSTY WINDS FROM 45 TO 55 MPH...UP
TO NICKEL-SIZED HAIL...TORRENTIAL DOWNPOURS...OR A COMBINATION OF
THESE ARE POSSIBLE. LIGHTNING IS THE NUMBER ONE WEATHER RELATED
KILLER IN FLORIDA. TREES AND OPEN SHELTERS OFFER NO PROTECTION. THESE
WINDS CAN DOWN SMALL TREE LIMBS AND BRANCHES...AND BLOW AROUND
UNSECURED SMALL OBJECTS. SEEK SHELTER IN A SAFE BUILDING UNTIL THE
STORM PASSES.

LAT...LON 2594 8056 2601 8025 2568 8032 2564 8051
TIME...MOT...LOC 1959Z 175DEG 10KT 2576 8042

$$
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Quoting Patrap:


Its in line with Masters.

You know, the one with the PHD here.

; )

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.


The CMC suggests the bigger dry air problem will actually be to the south from subsidence-caused dry air in the Caribbean being drawn up into the circulation.

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Member Since: March 16, 2012 Posts: 127 Comments: 7928
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Quoting Minnemike:
funny, i was just checking out the CIMSS precipitable loop, and it looks like the moisture field is diminishing around 99L, north/south.. if it starts to gain latitude, it might be ingesting a lot of dry air for a while. i don't really consider myself knowledgeable though.. don't quote me!


Its in line with Masters.

You know, the one with the PHD here.

; )

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.
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Convection increasing in the NW quadrant just like Grothar said it would.
Member Since: March 16, 2012 Posts: 127 Comments: 7928
Quoting Grothar:
Coming into full view. Plenty of moisture ahead.

funny, i was just checking out the CIMSS precipitable loop, and it looks like the moisture field is diminishing around 99L, north/south.. if it starts to gain latitude, it might be ingesting a lot of dry air for a while. i don't really consider myself knowledgeable though.. don't quote me!
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99L will track just north of trinny give pottery aand and he's island friends to the north some rains they have been asking for
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rainfall.over.panama.columbia.is.weakening
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Afternoon everyone.

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