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 homelesswanderer:


Do you have a link to that? Mine shows New Orleans. Thanks.
You could be right ,I was in a hurry.However this model for a long time showed it going up the east coast..Much further west now..
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3336. jipmg
Also I would monitor ex TD 2.. the shear that was holding it back from regenerating yesterday isn't there today.. and the convection is really firing up
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3335. cg2916
Quoting Stormchaser2007:
Close to the edge.

Still exposed to the west.
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August 14

0 - 0 - 0

continues...
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GOES-12 Maneuvers/KOZ for today...

Link
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Quoting Funkadelic:
I think hurricane David from 1979 is the best storm to compare this one to. The track that David had could definetely happen to 90L.





Link


Do me a favor and look back at Hurricane Georges. I seem to remember that storm starting out as a very big wave in the same area. Curious to see if the current computer models are anything close to it's old track.
Thanks, at work.
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3331. jipmg
Quoting homelesswanderer:


I don't know about that. Ike caused an insane amount of damage for a cat 2. Because he was so big and pushing so much water. He had cat 4 storm surge or higher. Now the winds may be a different story or may be not. We took a direct hit from a cat 3 that took out 50% of the tree canopy. Yes the wind damage was a lot worse. However Ike was a hundred miles away and he brought down a healthy 20% more.


exactly, a larger storm would be a very dangerous one, could you imagine the amount of damage Andrew would have caused had it been the size of Katrina if it hit SFLA? We'd get tropical storm force gusts all the way up through central florida.
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Convection has really tightened on 90L overnight. I think T.D. by 5pm today.
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3329. IKE
Quoting BajaALemt:
I've been looking for mentions of it too, Ike. Not seeing anything either *shrugs*


I don't see this one turning out-to-sea for at least 7-8 days.

Maybe I'll be wrong and the ECMWF is correct.
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Quoting tornadofan:
Looking at some of these motion shots, 90L looks like she's experiencing some dry air problems in the northeast quadrant. This should keep it from rapid strengthening and being weaker, on a more southern path.
Yes, but it has an anticyclone placed over it so shear shouldn't be a problem, but i agree with the souther path, is you mean it as in impacting the northern Antilles.
Good morning Dr Masters
and the "main blog bunch" LOL

Been lurking here a little over the past week; not really posting.

It appears I will be lurking a
lot more in the next week or so.

Sure hope those storms do turn out to be fish storms
and do not threaten any of us along the coast.

Keep the info coming,
it is much appreciated!

Happy Friday,
Gams
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Quoting nrtiwlnvragn:
The gfs ensemble members from the 00Z run indicate 90L may have some recurvature. Long way out on the ensembles (they run out to 384 hours).




hmmmm brings back memories of David in 79 (red track) Floyd in 99 (ensemble members to the right)
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3325. MahFL
Closer view.

ex TD2
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3324. IKE
Quoting P451:


6z nogaps



Thanks...I didn't know how to do that.
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Close to the edge.
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I've been looking for mentions of it too, Ike. Not seeing anything either *shrugs*
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3321. IKE
Quoting BajaALemt:
Here's another one you might be interested in, Ike....if you don't already use it.

SE WRF Link


More rains...lol...don't need any.
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Quoting palmpt:


Probably not going to turn until it hits the Gulf...
That's what I think but only a few models are hinting it into the Gulf.
Looking at some of these motion shots, 90L looks like she's experiencing some dry air problems in the northeast quadrant. This should keep it from rapid strengthening and being weaker, on a more southern path.
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Quoting depalma13:


What? Of course a larger hurricane will cause damage to a larger area, but a Cat 4 will cause far more devestation than a large Cat 2 even if it is over a smaller area.


I don't know about that. Ike caused an insane amount of damage for a cat 2. Because he was so big and pushing so much water. He had cat 4 storm surge or higher. Now the winds may be a different story or may be not. We took a direct hit from a cat 3 that took out 50% of the tree canopy. Yes the wind damage was a lot worse. However Ike was a hundred miles away and he brought down a healthy 20% more.
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3316. MahFL
ex TD2 now has very cold cloud tops, white on the Hurricane Sat.

Enhanced IR
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Quoting Stormchaser2007:
Good morning everyone, looking at that satellite it does look like 90L has shrunken overnight but has become much more organized, for right now track wise i am assuming that 90L will affect the upper Antilles but after that it's kind of cloudy track wise, models are hinting a Major Hurricane by the time it reaches the northern Antilles.
3314. IKE
Quoting BajaALemt:
Mornin' folks....

Here's a link to latest AFD's for San Juan...Link

Mornin' Ike...LOL, you're the only other person I see that's as avid an AFD reader as I am :P :P


Good morning...don't see much mention from any weather office out to Amarillo....Chicago...about a strong trough the end of next week.
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3313. palmpt
Quoting CaneWarning:
One of the local mets said this morning that if he had to guess where 90L would eventually go he said he would look at the Floyd track. He thinks it will get close to the east coast of Florida, turn and head up into Carolina.


Probably not going to turn until it hits the Gulf...
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Quoting depalma13:


What? Of course a larger hurricane will cause damage to a larger area, but a Cat 4 will cause far more devestation than a large Cat 2 even if it is over a smaller area.


From the NHC:

"A Category 4 hurricane would have winds between 131 and 155 mph and, on the average, would usually be expected to cause 100 times the damage of the Category 1 storm."
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Here's another one you might be interested in, Ike....if you don't already use it.

SE WRF Link
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One of the local mets said this morning that if he had to guess where 90L would eventually go he said he would look at the Floyd track. He thinks it will get close to the east coast of Florida, turn and head up into Carolina.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Hey West nice to c ya here. I have been lurking...of course I begin to see models in agreement this far out? Take care.
Quoting WetBankGuy:


If New Orleans gets a windstorm, it may resolve some of our lingering problems with abandoned post-K/flood houses.
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Quoting Stormchaser2007:
great visible stormchaser
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One year ago today a tropical wave over the Dominican Republic was getting organized. On Aug 15th 2008 it was named Fay.
CRS
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Quoting jipmg:


Yes, chances are a category 2 hurricane with a 400 mile wind field would cause much more damage to a larger area in comparison to a category 4 hurricane with a wind field of about 100 miles


What? Of course a larger hurricane will cause damage to a larger area, but a Cat 4 will cause far more devestation than a large Cat 2 even if it is over a smaller area.
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my guess based on all i have seen we may have TD 3 either by 11Am or most likely by 5Pm
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Mornin' folks....

Here's a link to latest AFD's for San Juan...Link

Mornin' Ike...LOL, you're the only other person I see that's as avid an AFD reader as I am :P :P
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3301. jipmg
looks like 90L is getting a bit of shear on it..
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3300. IKE
Memphis,TN. extended doesn't even mention a trough....

"DEEPER MOISTURE WILL PUSH INTO THE MIDSOUTH MONDAY ON SOUTH WINDS
SURFACE AND ALOFT. HOWEVER...HIGH PRESSURE ALOFT WILL REMAIN
DOMINATE OVER THE REGION. THERE WILL BE ENOUGH INSTABILITY FOR A
CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS THE ENTIRE FORECAST
AREA...ESPECIALLY IN THE AFTERNOON AND EVENING. TEMPERATURES WILL
BE SEASONABLY HOT WITH HUMIDITY A LITTLE HIGHER THAN RECENTLY. THE
GFS AND ECMWF ARE SIMILAR IN SHOWING THIS WEATHER PATTERN WILL
CHANGE LITTLE THROUGH THURSDAY WITH A DAILY CHANCE OF SHOWERS AND
THUNDERSTORMS...AND SEASONABLY HOT.
"
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according to the shear maps extd2 is entering an area of low shear but if it gets to the islands quicker shear is near 20-30
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3298. fmbill
Quoting IKE:


Rainmaker.


LOL!!!
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thanks ike.....oh well another rainy day...not like we are getting enough of these booming afternoon storms...
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Quoting IKE:


Rainmaker.


The NOGAPS handling of 90L is very poor, in fact it seems its gotten ex-TD2 and 90L mixed up in terms of strength.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting Funkadelic:
I think hurricane David from 1979 is the best storm to compare this one to. The track that David had could definetely happen to 90L.





Link


I go with that. I think we in the islands need to put last preps in place.
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10 knots and its showing. Low level clouds indicate that the circ is on the edge of the convection.


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3291. IKE
Long-term New Orleans,LA...

THE LONG WAVE UPPER TROUGH WILL BEGIN TO CUT OFF AN UPPER LOW
TODAY THROUGH SATURDAY. THIS FEATURE WILL HEAD WEST WITH THE
STRONG TROPICAL WAVE CLOSE ON ITS HEELS. THE TROPICAL WAVE THAT
WILL EVENTUALLY AFFECT US IS CAUSING ISSUES OVER THE NORTH CENTRAL
CARRIBEAN...HISPANIOLA AND THE BAHAMAS THIS MORNING. AS IT INTERACTS
WITH THE STALLED BOUNDARY IN THE GULF...GLOBAL SOLUTIONS WANT TO
DEVELOP AN AREA OF STRONG CONVECTION ON THE EAST SIDE OF TWO UPPER
LOWS. THE FIRST IS THE TUTT LOW MOVING WEST OVER CUBA. THIS ONE
WILL SINK BENEATH THE SECONDARY CUT OFF LOW OVER THE NORTHERN
GULF. AS THESE TWO BECOME MERIDIONALLY ORIENTED...A VERY LARGE AND LONG
AREA OF CONVECTIVE ACTIVITY SHOULD BREAK OUT FROM THE WESTERN
CARRIBEAN THROUGH THE NORTHERN GULF. THE STRONGEST CONVECTIVE
BURSTS LOOKS TO MOVE INTO THE NE GULF WHILE THE WAVE CONTINUES ITS
PROGRESS WESTWARD BRINGING A DEEP LAYER OF MOISTURE TO OUR AREA.
THIS SHOULD ALSO CAUSE A PRETTY GOOD CONVECTIVE BURST OFF OUR
SHORELINE AS WELL BY SUNDAY AND MONDAY. WE WILL CONTINUE MONITORING
FETCH AND WIND STRENGTH ALONG THE MENTIONED FETCH OVER THE NEXT
FEW DAYS TO DETERMINE IF TIDES WILL BE AN ISSUE ALONG THE GULF
COAST BY MONDAY MORNING.

LONG TERM...
ONCE THE WAVE PASSES TO THE WEST...A QUICK BUT SHORT LASTING SURGE
OF DRY AIR SHOULD MAKE ITS WAY AROUND THE BERMUDA RIDGE AND GIVE
US A DRY WEDNESDAY. BY THE END OF THE WEEK...MOST ATTENTION WILL BE
ON THE TROPICS ONCE AGAIN AS THE NEXT WELL STRUCTURED TROPICAL
SYSTEM MOVES ACROSS THE ATLANTIC. DRAWING ANY CONCULSIONS AT THIS
TIME FROM US OR ANY OTHER MET OUTLET WOULD SIMPLY BE CONJECTURE.
SO ATTM...WILL ONLY SAY THAT THE SYSTEM AT ABOUT 28W 13N HAS THE
BEST CHANCES FOR BECOMING A TROPICAL STORM AND/OR HURRICANE.
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Quoting victoria780:
The latest 06 GFS ten Image Loop show it bypassing trough in 10 days and heading further west Tx/La border..


Do you have a link to that? Mine shows New Orleans. Thanks.
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3289. IKE
Quoting Nolehead:
3259. IKE 11:52 AM GMT on August 14, 2009
Quoting iluvjess:
22N 77W is worth watching...


NOGAPS takes that here...Florida panhandle.



as a......???


Rainmaker.
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3288. jipmg
Quoting Seflhurricane:
does anyone have any new shear maps


here you go:

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8shr.html
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Good morning everyone. My apologies for asking a question that has been asked before. Which of the GFS runs is the most accurate (I understand that it loses its accuracy the more days out it is)? I see 90L on my doorstep on the 25, for the 3rd time, this time with the 00Z run.

Thank you in advance. :)
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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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