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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837. IKE
Quoting extreme236:


Um no?

13/1745 UTC 10.9N 23.4W T1.0/1.0 90L -- Atlantic


Surprised it's not higher....
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Lots of t-storms popping up over Florida today. None here in Tampa...yet.
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90L just needs to consolidate a bit more before it becomes a depression. A lot of curved bands and such but its too broad right now.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Not pretty picture.....lets hope this changes.

Member Since: September 2, 2007 Posts: 177 Comments: 20430
833. IKE
Quoting Chicklit:

90L
Link


Looks like dry-air on the NE side. Notice how that section is void of much convection.
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Quoting wunderkidcayman:

ok so 90L could be ana and TD2 could become bill

Would not be one bit surprised if that scenario pans out.
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Quoting Chicklit:

90L
Link


Now that's impressive
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830. bwi
813 GOBS: Straight from the HPC site -- maybe they're were in a hurrry and did'nt poorfread.
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829. IKE
Quoting 92Andrew:
Is there vorticity associated with the blob of storms north of Hispaniola?


Yes...it was just added within the last 3 hours....

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90L
Link
Member Since: July 11, 2006 Posts: 14 Comments: 11034
Quoting largeeyes:
For it being nearly devoid of convection 6 hours ago, I find it's current situation impressive.


I agree, quite an impressive turnaround.
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826. IKE
Quoting largeeyes:
For it being nearly devoid of convection 6 hours ago, I find it's current situation impressive.


I've got 2 pair of glasses. I'll loan you one to take a good look. It's completely exposed...

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Is there vorticity associated with the blob of storms north of Hispaniola?
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Oh for petes sake.
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TD-2 Viz Loop,re-loaded with FLASh
Member Since: July 3, 2005 Posts: 414 Comments: 125476
For it being nearly devoid of convection 6 hours ago, I find it's current situation impressive.
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Quoting canesrule1:
I'm expecting 03L at the 5 O'clock advisory, and I think it will be a 35MPH TD.


Um no?

13/1745 UTC 10.9N 23.4W T1.0/1.0 90L -- Atlantic
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting StormFreakyisher:

Sux we gota act like the Gulf's barrier island to weakens storms before they hit the Gulf because we have to take all the damage but then again were used to it and don't want another storm hitting NOLA.


RUDE!!!! Gulf states have taken many hits without your barrier..
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TD 2 RainBow Image

T-storm's in One Lonely Quad,the Nw, wouldnt be classified as "impressive"


Member Since: July 3, 2005 Posts: 414 Comments: 125476
Quoting largeeyes:
TD2's convection is impressive, but it is all well west of the COC and being blown away as it fires. This will never become a TS until it can wrap some of that around it's core and that doesn't appear to be possible until shear drops dramatically.
i think you are using the incorrect word there.This is not impressive in my book:
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TD2's convection is impressive, but it is all well west of the COC and being blown away as it fires. This will never become a TS until it can wrap some of that around it's core and that doesn't appear to be possible until shear drops dramatically.
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Link

what is the blob in the gulf on Friday the 21?
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I'm expecting 03L at the 5 O'clock advisory, and I think it will be a 35MPH TD.
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Quoting bwi:
From HPC's 3-7 day afternoon "final issuance" discussion:
http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

ALL MODELS AND ESP MEANS OF GFS/ECMWF INDICATE A ROCKIES RIDGE AND
DOWNSTREAM TROF ALONG 90W-85W LATE PERIOD INTO LATE NEXT WEEK AND
WEEKEND. ORIENTATION OF THIS PATTERN WILL BECOME CRUCIAL IMPACTING
THE TRACK OF THE ATLANTIC TROPICAL SYSTEMS.

ATLANTIC TROPICS ARE FORECAST TO BE QUITE ACTIVE THIS
PERIOD...WITH MODELS TRACKING A COUPLE OF SYSTEMS MOVING WEST
ACROSS THE ATLANTIC. AT THIS TIEM TE SECOND OF THESE SYSTEM MAY
AFFECT THE LESS ANTILLES BY DAY 7 THURSDAY.


Did WS write this??
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TD 2 2km Storm Relative IR Imagery with BD Enhancement Curve


Time of Latest Image: 200908131715
Member Since: July 3, 2005 Posts: 414 Comments: 125476
811. bwi
From HPC's 3-7 day afternoon "final issuance" discussion:
http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

ALL MODELS AND ESP MEANS OF GFS/ECMWF INDICATE A ROCKIES RIDGE AND
DOWNSTREAM TROF ALONG 90W-85W LATE PERIOD INTO LATE NEXT WEEK AND
WEEKEND. ORIENTATION OF THIS PATTERN WILL BECOME CRUCIAL IMPACTING
THE TRACK OF THE ATLANTIC TROPICAL SYSTEMS.

ATLANTIC TROPICS ARE FORECAST TO BE QUITE ACTIVE THIS
PERIOD...WITH MODELS TRACKING A COUPLE OF SYSTEMS MOVING WEST
ACROSS THE ATLANTIC. AT THIS TIEM TE SECOND OF THESE SYSTEM MAY
AFFECT THE LESS ANTILLES BY DAY 7 THURSDAY.
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Orange

Think TD2 will ever make it?
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No GFDL line on the current map. Does it not develop the new invest? Or is the last run just too old to put on the map?
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Quoting stormno:
lefty is that you...the old lefty the katrina one lol...im stormtop guy lefty im looking at something that could really potentially be very dangerous..i just got the info a few minutes ago...let me know if you are one in the same lefty from va beach i believe...Stormtop
Awesome! Stormtop and Leftyy420 back in the blog. It's gonna be an exciting season. :D Heya, Leftyy. Long time, no see.
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TD2 is firing up convection during DMIN than was the case during DMAX last night. If it could hold these storm together through DMAX, it may awake from it's coma.
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Quoting stormpetrol:
I suspect 90L will make it TD3 status by 11 pm, hell might even be Ana by 11 pm, and td2 will be like the song "still a hanging on"

ok so 90L could be ana and TD2 could become bill
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If the convection in the bahamas can continue to sustain itself through tonight then things could possibly change.. The mesoscale can form its own low pressure and will in turn create its own environment. I am not expecting this to happen however.. but it is good to keep you eye on things close to home.
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One more thought. HWRF is spinning up a typical cat 4 pressure with cat 2 winds? We have seen some storms with lower-than-expected winds for observed min pressure lately, but...
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Quoting nrtiwlnvragn:


You got me there, I don't know that much detail into the model. Could it be the 900 mb is overdone?

Sure...could be. Or could be the interpolation of sigma levels (for model run) to pressure levels (for output) is the source of the high numbers at 900 mb and/or low at 10 meters.
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Enhanced Infrared (IR) Imagery (1 km Mercator, MODIS/AVHRR)

Time of Latest Image: 200908131310
Member Since: July 3, 2005 Posts: 414 Comments: 125476
Quoting TropicTraveler:
Today is the anniversary of Hurricane Charlie.


Charley
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800. IKE
Quoting OSUWXGUY:
At least on the Precipitable Water Loop, TD2 has a fairly nice envelope of moisure. Though as discussed earlier...plenty of shear still to contend with...


Being as expansive as 90L is, it too may have some (albeit minor) issues with dry air itself. You can see a tight gradient (change in colors) to the north of 90L near the African Coast at the end of the loop.
Something so large pulls air from so far away..I guess some is bound to be dry :-)


I see some dry-air getting to the NE side of it.
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Quoting atmoaggie:

Still think the reduction might be overdone...especially at sea.


You got me there, I don't know that much detail into the model. Could it be the 900 mb is overdone?
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Today is the anniversary of Hurricane Charlie.
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Quoting cchsweatherman:


How eerily reminiscent.

thank-you for spelling that correctly :)
Member Since: July 11, 2006 Posts: 14 Comments: 11034
Quoting stormpetrol:
TD2 looks like it might have started that wnw movement.

more like north of dew west
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At least on the Precipitable Water Loop, TD2 has a fairly nice envelope of moisure. Though as discussed earlier...plenty of shear still to contend with...


Being as expansive as 90L is, it too may have some (albeit minor) issues with dry air itself. You can see a tight gradient (change in colors) to the north of 90L near the African Coast at the end of the loop.
Something so large pulls air from so far away..I guess some is bound to be dry :-)
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Quoting nrtiwlnvragn:


Varies on the height, from 80-95%. I looked at the actual model output at 126 hours, which on the FSU site shows surface winds of 107 kt.

http://moe.met.fsu.edu/tcgengifs/hwrf/2009081312-invest90l/slp21.png

Still think the reduction might be overdone...especially at sea.
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I suspect 90L will make it TD3 status by 11 pm, hell might even be Ana by 11 pm, and td2 will be like the song "still a hanging on"
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Quoting atmoaggie:

considering the min SLP is 932 mb, 900 mb isn't so far from the surface (even at RMW). Standard reduction from 900 mb to the surface may not quite apply.


See 784, I used actual model output at 126 hours, 10 meter surface wind.
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TD2 looks like it might have started that wnw movement.
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788. IKE
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Quoting Patrap:



Never say NO so far out,..nature has a way of making one er,blush real bad like.

Nothing is a Given with 90L.
Continue to Follow the NHC for the words on Track when and IF it forms


Yeah, the GOM is one of the main three possible tracks.
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About JeffMasters

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