Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. 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 was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


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

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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Quoting juniort:


where are you at?


West palm beach
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Quoting BajaALemt:
LOL @ the whole run. Central FL, hop across the state into the gulf then make a straight north beeline for Appilachicola :)) . I think it's trippin!

You guys talking about the precip or the center?
I see Fla straits...or very near to it for the center.
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3632. JLPR
Quoting Relix:
I am starting to think PR will get a double hurricane hit =(


NO shh! xD
They will go north, have faith =]
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3631. juniort
Quoting weatherboykris:
So now not one but two storms heading in my direction....adrenaline is starting to pump XD.


where are you at?
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Give it up for Dr. Masters, his headline read 'TD 2 may rise again'
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http://www.wunderground.com/wundermap/?lat=26.78485&lon=-80.22217&zoom=6&type=hyb&units=english&rad=0 &wxsn=0&svr=0&cams=0&sat=0&riv=0&mm=1&mm.mdl=GFS&mm.type=SURPRE&mm.hour=216&mm.opa=100&mm.clk=2&hur= 0&fire=0&tor=0&ndfd=0&pix=0

put model run at 216 hours ouch for anyone in palm beach and martin counties
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Quoting KEEPEROFTHEGATE:
what the models say and what you get are always two different things


I believe you had TD2 completely dead! Nice job!
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talkin about td2,the stronger it gets,the further north it would get pulled atleast thru 96hrs...
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3626. Relix
I am starting to think PR will get a double hurricane hit =(
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Quoting TampaSpin:
Sorry but TD2 could be a Hurricane by the time it reaches Puerto Rico


Could be. I think the NHC is looking for persistence with TD2 before making any calls about its intensity
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ok all wish storm will be anna or bill 1st??
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Guys, let's not start pinpointing a county in Florida where it's going to make landfall. That's crazy!
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Quoting KEEPEROFTHEGATE:
what the models say and what you get are always two different things


Whatever......WOW!
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and then the FL panhandle.
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looks like we should have ana by the 11am tomorrow,IMO,a compact system...but that might change in time....
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As Clint Eastwood said...... Right turn, Clyde.
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Sorry but TD2 could be a Hurricane by the time it reaches Puerto Rico
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3616. KEEPEROFTHEGATE (Mod)
HurricaneErnesto2006

you shall be replaced whith empty space just like whats in your head

have another drink looks like ya need it
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00Z GFS shows direct hit on martin county/palm beach county line and then transverses into GOM.

Also when makes landfall storm is as strong as the gfs can register
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so Florida is in the cone (for now).... let's all just keep in mind that we should not be concentrating on the black line! Everyone within the cone should monitor the storm.
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S. FL hit for 90L again on 00Z GFS run.
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LOL @ the whole run. Central FL, hop across the state into the gulf then make a straight north beeline for Appilachicola :)) . I think it's trippin!
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Bed time for me. see you all tomorrow
Member Since: August 19, 2006 Posts: 0 Comments: 15948
3608. 7544
fla in th e cone
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Quoting reedzone:
That track has it heading more towards Central Florida.


That'll probably change several times.
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3606. KEEPEROFTHEGATE (Mod)
Quoting TampaSpin:


Ya i did not look at the model run i just looked at the pic....and asumed that was TD2....i don't believe TD2 will die out now tho......i don't believe the models are accurate now at all......
what the models say and what you get are always two different things
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So now not one but two storms heading in my direction....adrenaline is starting to pump XD.
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Until Td 2 shifts wnw or nw, that forecast track will continue to shift west. It has been doing so for several days.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
OK
I can go to bed not... not happy, but relieved I guess.

Current NHC forecast shows 60 mph tropical storm centered 50 miles from my house at 8 am Tue Morn.

could be worse.

Good night

CRS
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Whoa, interesting... told my folks yesterday about TD2, they kinda blew it off. Hope they are paying attention.
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Quoting extreme236:


RELATIVELY LOW SHEAR IS FORECAST BY THE SHIPS MODEL FOR THE NEXT DAY
OR SO WHILE THE SYSTEM REMAINS UNDER THE SOUTHWEST PORTION OF AN
UPPER HIGH OVER THE CENTRAL ATLANTIC.


Relatively low. I didn't make the map that shows 20 knots immediately N of it now
Member Since: August 19, 2006 Posts: 0 Comments: 15948
Quoting wxmanjarod:
Has anyone else noticed that the 18z runs for the past few days have run 90L south? And, the 0z, 6z runs have run it north or on a re-curve?

Possibly, ridge builds stronger during the afternoon, leading to an initialization flaw? At night, ridge weakens a tad and the solution generates a stronger trough to create weaknesses in the ridge late next week?

Educated thoughts/opinions?

Mis-attribution of the measured values...not assigning enough to the diurnal effects? I think I can see how that might happen, yes.

But what in the world could one do about it? Just how many of the millibars analyzed for a high depends on the time of day and how much has nothing to do with the time of day?

I hear what you are saying, but am at a loss as to how one might account for except in MOS or raw interpretation (which, I suppose, is what we are doing).
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Quoting Weather456:



nope

Td 2 dies

90L intensifies

and a new wave develops behind


Ya i did not look at the model run i just looked at the pic....and asumed that was TD2....i don't believe TD2 will die out now tho......i don't believe the models are accurate now at all......
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That track has it heading more towards Central Florida.
Member Since: July 1, 2008 Posts: 13 Comments: 7437
Holy sh**

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Quoting kmanislander:
I posted about this earleir but here it is again. Ex TD2 has been coming under increasing shear from a digging ULL to the N. Shear is now 20 knots cutting across the top of it with more to come.

Here is the shear tendency map. It has been increasing all day in the path of Ex TD2. Click on the shear amp and you will see how the 20 and 30 knots of shear is coming down from the N.





RELATIVELY LOW SHEAR IS FORECAST BY THE SHIPS MODEL FOR THE NEXT DAY
OR SO WHILE THE SYSTEM REMAINS UNDER THE SOUTHWEST PORTION OF AN
UPPER HIGH OVER THE CENTRAL ATLANTIC.
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SATELLITE IMAGERY INDICATES THAT THE REMNANT CIRCULATION OF TROPICAL
DEPRESSION TWO HAS REGENERATED INTO A TROPICAL CYCLONE. DATA FROM
A NOAA G-IV MISSION...NOAA BUOY 41041...AND A RECENTLY-RECEIVED
ASCAT PASS INDICATES THAT THE CIRCULATION IS WELL-DEFINED. THE BUOY
ALSO REPORTED 1006.4 MB AND NORTH-NORTHWEST WINDS OF 19 KT.
ORGANIZED CONVECTION HAS NOW PERSISTED NEAR THE CENTER LONG
ENOUGH TO CONSIDER THIS SYSTEM A TROPICAL DEPRESSION. THE INITIAL
INTENSITY IS SET TO 30 KT...IN AGREEMENT WITH A SPECIAL DVORAK
CLASSIFICATION FROM TAFB AND WINDS FROM ASCAT.

THE INITIAL MOTION ESTIMATE IS 270/13. THE GLOBAL MODELS ARE IN
AGREEMENT THAT DEEP LAYER RIDGING WILL PERSIST NORTH OF THE
TROPICAL CYCLONE FOR THE NEXT SEVERAL DAYS...WHICH SHOULD STEER THE
SYSTEM IN A WEST OR WEST-NORTHWESTWARD DIRECTION. IN A FEW
DAYS...THE CYCLONE WILL BE APPROACHING THE WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE TO NORTH...WHICH COULD ALLOW THE SYSTEM TO MOVE
MORE TOWARD THE NORTHWEST. FOR SUCH A WEAK SYSTEM...THE TRACK
GUIDANCE IS IN GOOD AGREEMENT THROUGH THE PERIOD...AND THE OFFICIAL
FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS. HOWEVER...NOW THAT
THE SYSTEM IS BEING INITIALIZED AS A TROPICAL CYCLONE IN MOST OF
THE GLOBAL MODEL FIELDS...IT WOULD NOT BE SURPRISING TO SEE CHANGES
IN THE GUIDANCE DURING THE NEXT COUPLE OF GUIDANCE CYCLES.

RELATIVELY LOW SHEAR IS FORECAST BY THE SHIPS MODEL FOR THE NEXT DAY
OR SO WHILE THE SYSTEM REMAINS UNDER THE SOUTHWEST PORTION OF AN
UPPER HIGH OVER THE CENTRAL ATLANTIC. THEREAFTER...AN UPPER TROUGH
TO THE NORTHWEST OF THE TROPICAL CYCLONE COULD INDUCE SOME WESTERLY
SHEAR. GIVEN THIS...THE INTENSITY FORECAST ONLY SHOWS SLOW
INTENSIFICATION THOUGH 48 HOURS AND LITTLE CHANGE AFTER THAT. THE
OFFICIAL FORECAST IS CLOSE TO A BLEND OF THE SHIPS/LGEM/HWRF
MODELS. HOWEVER...IT IS WORTH NOTING THAT THE INTENSITY PROBABILITY
TABLE SHOWS ABOUT A 25 PERCENT CHANCE THAT THIS SYSTEM COULD BE A
HURRICANE AFTER 48 HOURS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 15/0430Z 14.6N 45.8W 30 KT
12HR VT 15/1200Z 14.7N 47.6W 30 KT
24HR VT 16/0000Z 15.0N 51.0W 40 KT
36HR VT 16/1200Z 16.0N 54.5W 45 KT
48HR VT 17/0000Z 17.0N 58.0W 50 KT
72HR VT 18/0000Z 19.5N 65.0W 50 KT
96HR VT 19/0000Z 22.0N 71.0W 50 KT
120HR VT 20/0000Z 25.5N 76.5W 50 KT

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two systems to deal with in 1 week.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Recon found a TD

Member Since: July 24, 2005 Posts: 407 Comments: 19076
AAaargh...
pulling out what little hair I have left...

1230 AM AST SAT AUG 15 2009

...TROPICAL DEPRESSION TWO REGENERATES


Oh well.
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.
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Has anyone else noticed that the 18z runs for the past few days have run 90L south? And, the 0z, 6z runs have run it north or on a re-curve?

Possibly, ridge builds stronger during the afternoon, leading to an initialization flaw? At night, ridge weakens a tad and the solution generates a stronger trough to create weaknesses in the ridge late next week?

Educated thoughts/opinions?
Member Since: Posts: Comments:
Tropical Depression 2 is officially back!
Member Since: July 1, 2008 Posts: 13 Comments: 7437
3585. KEEPEROFTHEGATE (Mod)
000
WTNT42 KNHC 150426
TCDAT2
TROPICAL DEPRESSION TWO SPECIAL DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
1230 AM AST SAT AUG 15 2009

SATELLITE IMAGERY INDICATES THAT THE REMNANT CIRCULATION OF TROPICAL
DEPRESSION TWO HAS REGENERATED INTO A TROPICAL CYCLONE. DATA FROM
A NOAA G-IV MISSION...NOAA BUOY 41041...AND A RECENTLY-RECEIVED
ASCAT PASS INDICATES THAT THE CIRCULATION IS WELL-DEFINED. THE BUOY
ALSO REPORTED 1006.4 MB AND NORTH-NORTHWEST WINDS OF 19 KT.
ORGANIZED CONVECTION HAS NOW PERSISTED NEAR THE CENTER LONG
ENOUGH TO CONSIDER THIS SYSTEM A TROPICAL DEPRESSION. THE INITIAL
INTENSITY IS SET TO 30 KT...IN AGREEMENT WITH A SPECIAL DVORAK
CLASSIFICATION FROM TAFB AND WINDS FROM ASCAT.
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Weather456
What do you think of the blob behind 90L

Member Since: October 1, 2007 Posts: 81 Comments: 26516

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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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