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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Quoting DM21Altestic:


Ouch, looks like 90L is in some trouble...


Good thing 90L developed an Anti-Cyclone over it to protect from shear.
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cbs4 mets say that we need to monitor an approaching tropical system towards the end of next week???? HMMMMMMMMM
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1632. java162
Quoting rxse7en:
LOL!



you are way behind time.....
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Quoting WPBHurricane05:
Joe B. probably loves the 12Z GFS. Right up the East Coast.


Right up his alley
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1629. rxse7en
Quoting IKE:


After 21,000+ posts, I'll hang around.
LOL!
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Quoting Skyepony:
NW wind on the SW side of DR now..

Here's the nowcoast link again. Zoom in, turn on some surface obs~ can see them all imposed on the sat pic. It autorefreshes..
That really doesn't mean much in this situation because of the terrain. That area of the DR is VERY mountainous, and mountains can easily change their area's surrounding wind vectors.
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Chevycanes...Thanks for the link
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Quoting DM21Altestic:
my friend Drak (not the Drakoen on here) thinks that 90L will just die out...


Your friend Drakoen doesn't realize that almost all the models develop it, and most bring it to Hurricane strength. Tell him that for us please? :)
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Joe B. probably loves the 12Z GFS. Right up the East Coast.
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1623. java162
Quoting Weather456:


it is rather broad but continues to organize. I'm surprise at the red code so earlier but all indications that a TD is forming. T# stands at 1.0, so still has a ways to go.

The 12Z models continue to bring it close to the islands but trending out to sea. becuz 90L circulation is broad, the models will keep changing and we will not get a sound idea until a TD forms or the circulation becomes more defined.




thanks
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18z GFS isn't too different with intensity so far.
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1621. Dakster
Quoting Weather456:


it is rather broad but continues to organize. I'm surprise at the red code so earlier but all indications that a TD is forming. T# stands at 1.0, so still has a ways to go.

The 12Z models continue to bring it close to the islands but trending out to sea. becuz 90L circulation is broad, the models will keep changing and we will not get a sound idea until a TD forms or the circulation becomes more defined.



I don't like that track forecast, send it back for another one. That puts it through Hebert's Box. (yes, spelled without the first 'r')
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Who id DRAK?
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1617. Skyepony (Mod)
NW wind on the SW side of DR now..

Here's the nowcoast link again. Zoom in, turn on some surface obs~ can see them all imposed on the sat pic. It autorefreshes..
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Quoting P451:


That blob has been over the water all day long.
Maybe it's being enhanced by the heat from the land mass but it's not responsible for it in entirety.

This wave has been tracked since 55W. It's surged and waned along the way and will probably continue to do so.


Correct, but thats why it looks impressive too, because the land convection is merging with the system over water....
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Another dud for Hawaii:

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Link
Wind shear

Lots of diffluence over the Carib wave...
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1611. Drakoen
You have a friend named Drak LOL!!!!!!
Member Since: October 28, 2006 Posts: 57 Comments: 29864
Quoting java162:


what is your opinion on your invest 90


it is rather broad but continues to organize. I'm surprise at the red code so earlier but all indications that a TD is forming. T# stands at 1.0, so still has a ways to go.

The 12Z models continue to bring it close to the islands but trending out to sea. becuz 90L circulation is broad, the models will keep changing and we will not get a sound idea until a TD forms or the circulation becomes more defined.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Ouch.

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Quoting TampaSpin:


Thanks for the advice....it was all in fun since 99% was calling 90L Bill.....but your correct.


True true, anyway, just a coincidence that I put Bill & Myself on my avator, when we had met that one time at my golf course. Slick Willie may pull some more tricks on us down the line, hopefully a dissapearing act
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Quoting TexasHurricane:


train of storms....Which ones will affect land and where???
If no one knows where ex td2 or 90l are going; what makes u think they know where the storms over africa are going?
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1602. 21N71W
where is the rain !!!!!??? sitting under big blob but no rain yet....
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Quoting P451:
Just a hunch but I think it's going to rain in Florida in the coming days. Going out on a limb here.... :)



Most of the convection is from the heating of the day over Hispanola and Dominican Republic
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Love is all you need.

Lennon/McCartney (sp) ?
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link to models. Link
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1596. IKE
Long-term from Mobile,AL....

LONG TERM (SUNDAY THROUGH THURSDAY)...NO BIG CHANGES WERE MADE IN
THE LONG TERM. THE LATEST GFS DEPICTS A WEAK TO MODERATE TROPICAL
WAVE MOVING WEST ACROSS THE NORTHERN GULF. THIS FEATURE WILL ALLOW
DEEPER MOISTURE ADVECTION ACROSS THE CENTRAL GULF STATES AND THE CWA
BY SUNDAY THROUGH EARLY MONDAY. WEAK FORCING ALOFT COMBINED WITH THE
DEEPER MOISTURE WILL ALLOW FOR WIDESPREAD SHOWERS AND THUNDERSTORMS
TO MOVE ACROSS MUCH OF THE AREA...ESPECIALLY IN THE SOUTHERN
ZONES...SUNDAY THROUGH MONDAY. THE MAIN CONCERN WITH THIS PATTERN BY
SUNDAY WILL BE PERIODS OF VERY RAIN WITH SOME TRAINING CELLS POSSIBLE
OVER THE SOUTHERN HALF OF THE FORECAST AREA. DUE TO THE DEPTH OF THE
MOISTURE AND LIMITED SHEAR ALOFT...THE THREAT OF SEVERE WEATHER WILL
REMAIN LOW THROUGH EARLY NEXT WEEK.

BY TUESDAY...A WEAK INVERTED TROF AND BETTER DEEP MOISTURE SHIFTS
WEST OF THE AREA WHICH WILL RESULT IN GRADUAL CLEARING AS WEAK
SURFACE HIGH PRESSURE BUILDS ACROSS THE AREA. ISOLATED TO SCATTERED
POPS MOSTLY FROM AFTERNOON HEATING AND A WEAK SEA-BREEZE EACH DAY IS
EXPECTED. BY LATE IN THE WEEK...A MIDDLE TO UPPER TROF MOVES EAST AND
DEEPENS OVER THE EASTERN CONUS WHICH COULD HAVE A SIGNIFICANT IMPACT
ON THE TRACK OF ANY TROPICAL FEATURE THAT MOVES WEST INTO THE WESTERN
ATLANTIC OVER THE WEEKEND.
WILL STAY CLOSE TO THE CURRENT MEX
GUIDANCE FOR TEMPS AND POPS THROUGH THE EXTENDED PERIODS.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting P451:
Just a hunch but I think it's going to rain in Florida in the coming days. Going out on a limb here.... :)



Woohoo! :D
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1594. Dakster
Quoting StormSurgeon:
What is that big yellow for?


An area of concern with low probablilities of becoming a tropical storm in the next 48 hours. However, it will soak a bunch of areas in the Carribean before it dissipates.
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Quoting conchygirl:
I'm with you on that TS!

I think we go to bed knowing TD2 is a remnant low and we wake up with newly re-born TD2
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The area in yellow will not have time to develop before crossing Florida, however it might further develop in the GOM?
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1591. KEEPEROFTHEGATE (Mod)
Quoting sarasotaman:
Here we go agian with the lack of the freedom of speech! The polls ask about storms. so if you don't like it use your ignoe button!!
no problem while iam at it i will drop wunderyakusa an email and i can assure you the polls will be gone real quick i always ask nice first then i let admin decide
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Jeez...and the CMC spins another one up behind future Ana.
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Quoting DestinJeff:
.9. The word "poleward" (many people know this as simply North)



You do realize the earth is made of two hemispheres, right?
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Hello... Can anyone provide a link to the models? Just got a new computer..updating links.
Thanks.
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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.