TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 2:38 PM GMT on August 13, 2009

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Tropical Depression Two is near death, but is still worth watching. The dry, Saharan air to the north and west of the depression, combined with moderately high levels of wind shear of 15 - 20 knots, have almost completely destroyed all of TD 2's heavy thunderstorms. Satellite loops of the storm show a well-formed circulation, but almost no heavy thunderstorm activity.

Wind shear over TD 2 is expected to remain in the modereate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C three days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to to TD 2's north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that TD 2 will not be able to intensify quickly, and some of the models indicate the TD 2 may get destroyed in the next day or two. However, several models still predict TD 2 will become a tropical storm. The HWRF model predicts TD 2 will become a hurricane five days from now, but this seems unlikely given the dry air and relatively high wind shear affecting the storm.


Figure 1. Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

African tropical wave 90L
A strong tropical wave with a large circulation and plenty of heavy thunderstorm activity is a few hundred miles south of the Cape Verdes Islands, off the coast of Africa. NHC dubbed this disturbance 90L this morning. This morning's QuikSCAT pass shows that 90L has a very large circulation, and top winds of about 30 mph. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are in two major bands, to the north and to the south of the center. There is no heavy thunderstorm activity near the center yet, and this would have to happen before 90L can be named Tropical Depression Three. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two has been. Wind shear is about 20 knots over 90L, and is forecast to remain in the moderate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days, which are high enough above the 26°C threshold for tropical cyclone formation to allow some slow development to occur. The GFS and ECMWF models continue to predict the development of this wave, though they are now less aggressive about intensifying it than they were in earlier runs. The consensus among the reliable HWRF, GFDL, GFS, and ECMWF models is to bring 90L to point near or just north of the northernmost Lesser Antilles Islands 6 - 8 days from now. The storm could be at hurricane strength by then, as forecast by the SHIPS intensity model.

I'll have an update Friday morning.

Jeff Masters

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1287. Patrap
Quoting tarpontexas:
Patrap...thanks for the video on hot towers. very informative



Always like to keep it real and informative,thanx(everyone)
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Quoting tallahasseecyclone:
Is the TCFA used to let people know that it's time to Blog up?


LOL yeah I guess, in a way.
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Quoting TampaSpin:
These are the most current runs



Not looking good for our island friends.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
1284. Drakoen
It will be interesting if TD2 can get just north of the Lesser Antilles and into the Bahamas. Favorable conditions there south of a high pressure system.
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Quoting tallahasseecyclone:
The Weather Channel is the worst channel on television. I flip over to CSPAN when I get bored of the crap on there. They need to make a "it could happen tomorrow" about what the world would be like if their channel didn't stink so bad.

Please enough, I have had it with the weather channel.They changed so much they are trying to act like an entertainment show, they lost all the primary focus on weather itself and lack in detail of it such as hurricanes now.
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Is the TCFA used to let people know that it's time to Blog up?
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These are the most current runs

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Convection is still some what on the scattered side BUT overall organization has improved.Should be a TD during the next 1-2 days.

View of both systems...

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Quoting kingzfan104:
what are those? Should I look at those or the computer models?


They are computer models. Basically they feed slightly different input data into the same model and re-run. This shows the range of possibilities and model uncertainty. As you can see, anything from entering the GOM to curving out to see east of the US is possible.
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Quoting Drakoen:


Drakster I'm just seeing a big red X.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Continues to organize.

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1273. Drakoen
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I was just think of something and I thought it was interesting.

Just as it is quite possible that we are going to see our A name form from a TD other than TD1, it's possible (not this year) to have a B storm, for example form from TD1 and have the A storm form from TD2. Pretty cool I think. I wonder, has it ever happened before?

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1222, so flame yourself if you wish, that's your prerogative and i what i said was a serious concern on my part.
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1270. KEEPEROFTHEGATE (Mod)
Quoting HurricaneGeek:
Does the TCFA that was issued bare any significance to the 5 pm NHC update?
no not till the time the TCFA reachest it assign time for update if it goes to a TCFW then adv. will be a good bet from NHC it is what it is first alert in 6 hrs the update it will either remain a alert or go to warning or be cancelled
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting TerraNova:


There is a TCFA. A TCFA doesn't mean a system has already formed but rather that the formation of a system is imminent.
okay just wanted to know, when i read that i said we have TD 3 already wow but it was not that
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1268. WxLogic
18Z NAM showing quite a moisture surge "almost organized" from the TW N to S of Hispanola...
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1267. Drakoen
Yes, StormChaser2007
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1265. Drakoen
Quoting kingzfan104:
what are those? Should I look at those or the computer models?


Those are variants of the GFS with slightly different conditions.
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Quoting Seflhurricane:
then why are some on here saying that a tropical cyclone formation alert was issued ???????


There is a TCFA. A TCFA doesn't mean a system has already formed but rather that the formation of a system is imminent.
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1263. HadesGodWyvern (Mod)
TCFA can be issued 24-36 hours before the formation of cyclones if conditions are favorable for development
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1262. IKE
From Key West afternoon discussion....

"A TROPICAL WAVE...CURRENTLY LOCATED ALONG
68W SOUTH OF 21N...WILL BE MOVING INTO THE FLORIDA STRAITS FRIDAY
NIGHT. THIS TROPICAL WAVE WILL PASS ACROSS THE FLORIDA KEYS
SATURDAY. THE 12Z GFS NUMERICAL MODEL GUIDANCE DEPICTS A LESS
AMPLIFIED TROPICAL WAVE AND LESS ATMOSPHERIC MOISTURE ASSOCIATED
WITH IT IN THE VICINITY OF THE FLORIDA KEYS COMPARED TO PREVIOUS
MODEL RUNS. GIVEN THE INVERTED-V STRUCTURE APPARENT ON SATELLITE
IMAGERY AND DEEP MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE
WATER IMAGERY...THE GFS SOLUTION SEEMS UNLIKELY. THEREFORE...THERE
WILL BE NO CHANGES TO THE POPS FORECAST FOR FRIDAY NIGHT THROUGH
SATURDAY NIGHT.

.LONG TERM (SUNDAY THROUGH THURSDAY)...
AN ATLANTIC RIDGE OF HIGH PRESSURE WILL BUILD ACROSS THE
SOUTHEASTERN UNTIED STATES SUNDAY THROUGH THURSDAY. TROPICAL
DEPRESSION TWO SHOULD OPEN UP OR WEAKEN TO A TROPICAL WAVE. IF THIS
IS THE CASE...THE TROPICAL WAVE SHOULD TRACK FARTHER SOUTH INTO THE
CARIBBEAN SEA. THIS TROPICAL WAVE MAY MAKE IT TO KEYS` LATITUDE BY
MID WEEK NEXT WEEK. THERE IS TOO MUCH UNCERTAINTY ASSOCIATED WITH
THIS FORECAST SCENARIO TO MAKE ANY CHANGES TO THE LONG TERM PORTION
OF THE ZONE FORECASTS FOR THE FLORIDA KEYS."
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Quoting Drakoen:
Those are some scary long range ensemble members and they show the range of possibilities.

These?

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Quoting Drakoen:


Look at the ensemble members


They are all over the place and I can say they think its headed for the US...or awfully close, not to mention the islands.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting Patrap:
Earth Full Disk Atlantic 2Sept 08

Hannah was supposed to knock up for a loop, but she was not unlike the garden variety nor'easter we get 2 or 3 times a year on the Jersey Shore. Talk about a dud! Joe Bastardi made her sound like biblical times in his forecast and...ZERO. It's not Joe B's fault, she could have potentially been a huge player, it just didn't work out that way.
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1257. ssmate
Quoting tarpontexas:
Patrap...thanks for the video on hot towers. very informative


Ditto
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then why are some on here saying that a tropical cyclone formation alert was issued ???????
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The Weather Channel is the worst channel on television. I flip over to CSPAN when I get bored of the crap on there. They need to make a "it could happen tomorrow" about what the world would be like if their channel didn't stink so bad.
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Interesting.

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1253. IKE
Quoting PcolaDan:


What would cause this considering their present locations? Strength? (weak stay south strong go poleward)


High pressure + it staying weak.
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1252. Drakoen
Quoting hurricane23:
100+mph in 5 days per SHIPS 18z...


Look at the ensemble members
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1251. HadesGodWyvern (Mod)
No indications of THREE from where I look at
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Quoting IKE:


TD2 looks to have a better shot of getting into the GOM vs. 90L.


What would cause this considering their present locations? Strength? (weak stay south strong go poleward)
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Quoting CaneWarning:


I miss John Hope. He was way better than anything TWC has now.


I was in a Chat with one of TAmpa Chief Mets last nite also....and trust me there alot of what the weather Channel has out there now....LOL
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Quoting popartpete:
Agreed. John Hope is probably rolling over in his grave.


I thought they had stopped with the HeadOn thing? Honestly I haven't really watched TWC in ages, not necessarily because they're bad but because I've found better sources for information.
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1247. KEEPEROFTHEGATE (Mod)
Quoting Vortex95:


already?
there is a high risk of 90l to cross populated areas namly cen to north windwards(456 and many others) virgin islands ne pr coast the earlier the warning the greater the chance of hieghten alert among the populated centres involved
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1246. Drakoen
Those are some scary long range ensemble members and they show the range of possibilities.
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100+mph in 5 days per SHIPS 18z...
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1244. RI92138
Someone asked yesterday if two hurricanes ever hit the same area within a week. I know that in 1954 Hurricanes Carol and Edna both hit Southern New England 10 days apart. Carol was on August 31 and Edna Sept. 11. Carol came ashore in New London, CT and Edna hit 100 miles east at Chatham, MA
Both had little if any warnings issued.
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1243. IKE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
228 PM EDT THU AUG 13 2009

.DISCUSSION...
SHOWERS AND THUNDERSTORMS FLARING UP THIS AFTERNOON OVER INTERIOR
AND WESTERN AREAS, AS FAR EAST AS THE WESTERN FRINGE OF THE EAST
COAST METRO AREA. THIS ACTIVITY IS MOVING NORTHWEST AND SHOULD
CONTINUE TO DEVELOP AND CONSOLIDATE OVER ALL BUT THE SOUTHEAST
METRO SECTIONS THROUGH EARLY EVENING.

DRIER AIR OBSERVED IN CIMMS MIMIC PRECIP WATER DATA MAKING STEADY
WESTWARD PROGRESS IN RESPONSE TO HIGH PRES BUILDING FROM THE NE.
THIS DRIER AIR WILL SPREAD OVER SOUTH FLORIDA TONIGHT INTO MUCH OF
FRIDAY, WITH LOWER POPS ANTICIPATED BOTH PERIODS. MAIN FEATURE OF
NOTE FOR THIS FORECAST PERIOD CONTINUES TO BE THE TROPICAL WAVE
CURRENTLY OVER HISPANIOLA AND THE TURKS AND CAICOS NEAR 71W.

TIMING OF THE WAVE PASSING THE AREA IS A LITTLE FASTER TODAY,
SOMETIME FRIDAY EVENING THROUGH PRE-DAWN HOURS ON SATURDAY. THE
GFS HAS MADE BIG CHANGES FROM PREVIOUS RUNS IN KEEPING THE BULK OF
THE DEEP MOISTURE BEHIND THE WAVE WELL TO THE SOUTH AND KEEPING
MUCH OF OUR AREA UNDER RELATIVELY DRIER AIR/SUBSIDENCE. IN FACT,
GFS HAS HIGHER POPS FRIDAY NIGHT WITH THE ACTUAL WAVE PASSAGE THAN
ON SATURDAY, WHILE THE NAM KEEPS HIGHER POPS ON SATURDAY. THE
DRIER CONDITIONS IN THE GFS MAY BE ATTRIBUTED TO INCREASINGLY
DIVERGENT LOW LEVEL FLOW FROM HIGH PRES BUILDING IN, ALONG WITH
LESSENING INFLUENCE FROM UPPER LOW OVER HISPANIOLA/CUBA REGION.
DUE TO OFTEN FICKLE NATURE OF TROPICAL WAVES IN THIS REGION, WILL
NOT LOWER POPS DRAMATICALLY AS PER GFS/MAV, BUT WILL SHOW A SLIGHT
DOWNWARD TREND ESPECIALLY IN THE PALM BEACHES.

WAVE SHOULD BE WELL WEST OF AREA SATURDAY NIGHT AND SUNDAY, WITH
DEEP LAYERED RIDGE CONTROLLING OUR WEATHER INTO EARLY NEXT WEEK.
THIS MEANS MODERATE EASTERLY FLOW AND CLIMATOLOGICAL TO SLIGHTLY
BELOW CLIMO POPS. NEXT TROPICAL WAVE TO AFFECT AREA NEXT WEEK AT
END OF THIS FORECAST PERIOD MAY BE REMNANTS OF TROPICAL DEPRESSION
TWO...
BUT THIS OF COURSE DEPENDS ENTIRELY ON ITS EVOLUTION OVER
THE NEXT FEW DAYS. PLEASE MONITOR ADVISORIES AND OUTLOOKS FROM NHC
FOR MORE INFORMATION.
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do we have any indications of TD 3 yet??????
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Does the TCFA that was issued bare any significance to the 5 pm NHC update?
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Quoting Nolehead:
geeez!!! i can't stand TWC, so much for the tropical at 50 before the hour...it's either the damn "oh it could happen now" or "storm stories"......I want my TWC2....


HEAD ON....."Apply directly to the forhead"


It's Hurricane Week, remember?
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Quoting popartpete:
Agreed. John Hope is probably rolling over in his grave.


I miss John Hope. He was way better than anything TWC has now.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting IKE:


TD2 looks to have a better shot of getting into the GOM vs. 90L.


And conditions might be favorable in the NE to Central GOM in 168-192 hours when ECMWF shows its remnants entering. Maybe something else to watch.
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Quoting Nolehead:
geeez!!! i can't stand TWC, so much for the tropical at 50 before the hour...it's either the damn "oh it could happen now" or "storm stories"......I want my TWC2....


HEAD ON....."Apply directly to the forhead"
Agreed. John Hope is probably rolling over in his grave.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.