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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i heard some of why its been queit was wind shear and sarah dust over the area
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Quoting TampaSpin:


Thats one of your better forecast jobs.......LMAO

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Quoting southfla:
Good evening (morning) all - I guess I will be firing up the generator this weekend. If something does head this way, it wouldn't be the first time S.Fla was under the gun around Aug 24rth.


I'll be doing the same thing this weekend as well as topping of my Hairy Cane supplies. Watched Max Mayfield on 10 tonight and he highly recommends South Floridians to get out this weekend and get their plans in order.....
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Quoting weathercrazy40:
that is true when watching sat loops seem these storms get a little quiet when they lose the sun`s heat
funny, I am no expert, but I think they fire up more when they lose the suns heat. I think that is what everyone has been referring to as dmax. correct me if I am wrong.
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Quoting KEEPEROFTHEGATE:
90l will fire all of its guns beginning tomorrow afternoon ramp up fast by end of tomorrow night going into sun morning

watch wait see


Thats one of your better forecast jobs.......LMAO
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If anyone might have an answer, I've been wondering if the MJO has anything to do with the sudden rise in activity in the Atlantic...
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Quoting wxmanjarod:


That's right, and those mathematical equations are based upon inaccurate assumptions of our atmosphere. We need to stop this conversation though, or I'll be dragging textbooks out before sunrise! I'm out for the night... I have a feeling everything will just be miles west of where it is now when the baby wakes me up in a few hours.

You probably will not read this, but do you remember that most all of our physics proofs start out with "assume the sin of theta equals theta"? Only actually happens when theta is zero...almost never for most of those physics principles.
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Sorry for the little break, but at 2AM I will start making my Tropical Analyzes on my blog again.
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that is true when watching sat loops seem these storms get a little quiet when they lose the sun`s heat
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3675. Walshy
When the tropics transitioned from the EPAC to the Atlantic, so did two storms so close to each other.

Lets hope 90L does not pull a Felicia and TD2 can stay a TS like that other storm in the EPAC.
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Quoting Orcasystems:


modeling : Use of mathematical equations to simulate and predict real events and processes.

Don't forget the GIGO principle.

Never.
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Quoting Orcasystems:


modeling : Use of mathematical equations to simulate and predict real events and processes.

Don't forget the GIGO principle.


That's right, and those mathematical equations are based upon inaccurate assumptions of our atmosphere. We need to stop this conversation though, or I'll be dragging textbooks out before sunrise! I'm out for the night... I have a feeling everything will just be miles west of where it is now when the baby wakes me up in a few hours.
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Quoting weatherblog:
This shouldn't be a surprise to South Florida since we are under the gun every year. Last year it was Fay and Ike.


It's more or less, I think, because this is the first potential United States landfall we've had all year, and not necessarily because it's south Florida.
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Quoting southfla:
Good evening (morning) all - I guess I will be firing up the generator this weekend. If something does head this way, it wouldn't be the first time S.Fla was under the gun around Aug 24rth.
I know right, my birthday is August 21st and many a Keys trip has been ruined by a storm scare or hit. I just hope this one, if it strengthens, doesn't come this way. Business here doesn't need a direct hit. Could be bad.
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..
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3669. KEEPEROFTHEGATE (Mod)
Quoting ackee:
TD#2 is the imediate concern now 90L has yet to live up to all the models hype
90l will fire all of its guns beginning tomorrow afternoon ramp up fast by end of tomorrow night going into sun morning

watch wait see
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This shouldn't be a surprise to South Florida since we are under the gun every year. Last year it was Fay and Ike.
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3667. JLPR
90L looking better and better



I wonder how is the circulation looking right now =P
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Quoting wxmanjarod:


I don't think there is anything you can do about it. That's just an old-fashioned global model flaw when you start looking past five days.

In general, I guess we have to remember that these are imperfect models and deal with it. *sigh* Thanks for the input though.


modeling : Use of mathematical equations to simulate and predict real events and processes.

Don't forget the GIGO principle.
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Ok, I need glasses.....LOL. Watching it frame by frame, I just couldnt SEE the 1018. Or maybe it's time to go to bed :)) I opt for bed.

Night folks! Have fun watching!
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Good evening (morning) all - I guess I will be firing up the generator this weekend. If something does head this way, it wouldn't be the first time S.Fla was under the gun around Aug 24rth.
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Quoting Funkadelic:


100% correct.

They dont want to jump the gun and predict a hurricane approaching Florida on the first forcast cone lol. Florida being in the cone this early is good, means it probabley wont hit FLA.
I totally agree. We're always in the cone early and then fade out gradually with an occasional hit on the lower southeast coast. This storm just reminds of _ndrew a little in how it formed then died and then formed again, although not in the same intensity by any means.
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3662. ackee
TD#2 is the imediate concern now 90L has yet to live up to all the models hype
Member Since: July 15, 2008 Posts: 0 Comments: 1376
Quoting atmoaggie:

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).


I don't think there is anything you can do about it. That's just an old-fashioned global model flaw when you start looking past five days.

In general, I guess we have to remember that these are imperfect models and deal with it. *sigh* Thanks for the input though.
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Quoting weathercrazy40:
i see for anyone still awake #2 is back again local forecaster seem to be more conserned with the one behind it for a chance of it going up the east coast to here in newengland

He mustn't be basing that on the 00 GFS.
The next wave after 90L goes right to the Caribbean and get destroyed by...are you ready for this...Montserrat. Little island shreds hurricane. After visit hurricane just gives up completely. Right.
G'Nite.
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GFS is the only model that shows 90L getting in the GOM, so my confidence of that happening is extremely low. Any long range track shouldn't be taken too seriously. All I would take from it is that it is going to affect the northern islands then head into the Bahamas and possibly into Florida.
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i see for anyone still awake #2 is back again local forecaster seem to be more conserned with the one behind it for a chance of it going up the east coast to here in newengland
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For the CONUS, it looks like Florida (south florida in particular) is going to have back to back storms. Better hope it dissipates before going into the Bahamas because it will bomb out otherwise on the hottest TCHP in the basin....same for 90L.
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TD2

90L

AOI

AOI
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Quoting BajaALemt:
Atmo, MSLP at 276

Link

That's right after the hard right out of the gulf. Watching that, on this run, it's like a huge weakness (more like a huge hole...lol) opens up....seems a little unreasonable.....to me anyway *shrugs*

I see. I thought someone said central FL, which I took to mean Atlantic coast central FL.
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Quoting hurricane23:


Actually the goes right were HPC has it around day 5-7 i believe.


Adrian, what do u think of our two systems? If they both blow up tonight or tomorrow I think we may start to see some interaction.
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3653. Skyepony (Mod)
Wunder how much recon made it in the 00Z run.
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heh this blog will hit 4,000 commets be for the night is done
Member Since: May 21, 2006 Posts: 5091 Comments: 115432
Quoting hurricane23:
What r you guys seeing landfall on the 0z GFS is in extreme southern florida.

I think someone might be focusing on the pretty colors in the precip forecast, rather than the isobars.
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Quoting Twinkster:
http://www.wunderground.com/wundermap/?lat=26.78485&lon=-80.22217&zoom=6&type=hyb&u nits=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


alright, i need help with this. i don't see anywhere that i can put it at 216 hours.
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Quoting reedzone:
00Z GFS just doesn't make sense when not only is it north of the islands, but a trough heading right towards it.. but still heads into the GOM.. Doesn't make sense.


a strong storm can plow right through a trough also if a trough encounters a strong ridge it can't influence the storm enough to change its path significantly
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Quoting weatherblog:
Guys, let's not start pinpointing a county in Florida where it's going to make landfall. That's crazy!


Thank you for that. It's a long way out yet...
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3647. ackee
the GFS dissipate TD#2 and its back not a beliver of the GFS I am willing to wait and see what will happen with 90L
Member Since: July 15, 2008 Posts: 0 Comments: 1376
Atmo, MSLP at 276

Link

That's right after the hard right out of the gulf. Watching that, on this run, it's like a huge weakness (more like a huge hole...lol) opens up....seems a little unreasonable.....to me anyway *shrugs*
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Quoting reedzone:
00Z GFS just doesn't make sense when not only is it north of the islands, but a trough heading right towards it.. but still heads into the GOM.. Doesn't make sense.


Actually the goes right were HPC has it around day 5-7 i believe.
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Quoting weatherblog:
Guys, let's not start pinpointing a county in Florida where it's going to make landfall. That's crazy!


SERIOUSLY. Thank you!
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3643. JLPR
Quoting TampaSpin:
Sorry but TD2 could be a Hurricane by the time it reaches Puerto Rico


How dare you say that XD
But I really hope it isn't one =P
or People here would freak out very fast
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Quoting reedzone:
00Z GFS just doesn't make sense when not only is it north of the islands, but a trough heading right towards it.. but still heads into the GOM.. Doesn't make sense.


Reed thats what i said it makes no sence....i think some of the models are screwed up also with the return of TD2
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Even that the models have their own version as to the intensity of the two sytems at hand, they all agree in the trajectory or at least they are significantly close. I see some impact either in Puerto Rico or Hispaniola and I would not be surprised if they keep south of those islands and make it to the GOMEX. Either case they need to be watched.
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Quoting FloridaTigers:


Could be. I think the NHC is looking for persistence with TD2 before making any calls about its intensity


100% correct.

They dont want to jump the gun and predict a hurricane approaching Florida on the first forcast cone lol. Florida being in the cone this early is good, means it probabley wont hit FLA.
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What r you guys seeing landfall on the 0z GFS is in extreme southern florida.
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What type of energy is going to be available for 90L TCHP
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3637. GatorWX
Quoting Weather456:
In 1 week, the GFS shows another area right behind 90L, what an onslaught.


pretty rapid turnaround, huh? Anyone still shooting for a 0-0-0 finish??? j/k, but it is a little surprising how quick things changed. Amazing what a little dust can do!
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00Z GFS just doesn't make sense when not only is it north of the islands, but a trough heading right towards it.. but still heads into the GOM.. Doesn't make sense.
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the Admins most be re moveing commts and baning at this time
Member Since: May 21, 2006 Posts: 5091 Comments: 115432
Quoting juniort:


where are you at?


West palm beach
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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.