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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1384. Drakoen
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1383. cg2916
Quoting dcoaster:
Is anyone else thinking 02L is looking impressive right around now?


I think it looks impressive, and 90L is getting there, but its circulation is elongated and winds are running through the center. Once the circulation tightens, winds should stop going through the center.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
1382. Patrap
Beware the Atlantic and Prepare now,to stay ahead of the Game.



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Anything that makes it into the Gulf is going to really blow up.
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Quoting txlori:
I don't say much...just read and try to learn. I am in Bayou Vista, a canal community just north of Galveston Island and I was glued to this blog last summer. As we all watched Ike, I read all the comments, the very educated and thoughtful speculation on the path and strength of the storm. I drove my husband crazy looking a model runs. I am pretty sure that Galveston was one of the LAST places anyone really thought Ike would land, yet it defied everything and everyone and did just that. I bet many of you will remember that guy who asked if Ike could hit Galveston when it was still way out and he got slammed. So I have learned not to discount anything, to assume anything or disregard someone's concern. Just be aware and prepared and learn what you can along the way. This is a great blog with a lot of folks who care and I really appreciate you! *Back to learning!*

And I remember Ike was heading right for Corpus Christi and all sorts of plans were made there for rapid response by the disaster agencies. All those plans had to change very quickly when the storm did what it wanted to in the end. Even a couple of days out we don't have a firm idea of where they'll go. I remember Charlie was supposed to hit Tampa and wondering how many more deaths and damage there would have been if it had - and then Ike hit Bolivar instead of straight on into Galvaston - where 20,000 people failed to evacuate. The outcome for them could have been quite different. I guess we all can speculate but in the end we have to wait for these capricious monsters to go where they want to.
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Quoting KEEPEROFTHEGATE:
now we got ants model runs whats next maybe we should have a tarot card reading while where at

lol

Back when nobody knew where Katrina was going, after reading MaryEsther's comments, I said on these boards throw out all the models and go with the ants. The ants, if used right, can be as good an indicator as any. Again, large mounds in unusual spots.
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1378. KEEPEROFTHEGATE (Mod)
i here tea leaf reading is pretty good

and we always have the flush model to fall back on

lol
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18:43 UTC Ascending pass.
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Quoting Patrap:
My NOLA ant has been in my Jack again..so He is oblivious as to anything ..



LMAO
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Quoting dcoaster:
Is anyone else thinking 02L is looking impressive right around now?

That quikscat is just over 12 hour old, lol.
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Quoting KEEPEROFTHEGATE:
now we got ants model runs whats next maybe we should have a tarot card reading while where at

lol


Good idea! Maybe we can also have someone read tea leaves and palms.
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Quoting mobilegirl81:
I know this sounds like folklore, but we always have lots of squirrels and ants here in Mobile,Al and we've seen no ants(none)and squirrels are here but you never see them and they have been packing the heck out of thier nests

We had reports of unusual ant activity near New Orleans back when Katrina was still a TD in the Bahamas. MaryEsther from Houma reported seeing ant mounds, big ones, in unusual spots. Like in a patch of grass next to McDonalds drive-thru. The soccer field was unusable as large mounds covered the field.
.
.
Personally, I think that there is something to the ant behavior that is scientific. Over the years, we've weeded out some stuff, like ants crawling up trees, or ants crawling into sidewalk cracks. But ant mounds I think remain as a sign. imo, unscientific.
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1372. KEEPEROFTHEGATE (Mod)
now we got ants model runs whats next maybe we should have a tarot card reading while where at

lol
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1371. Drakoen
Big difference between the ECMWF and the GFS 500mb long range mean
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02L has been taken off the cimss front page map:
Link
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P451 shear is decreasing around it though.
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Quoting weatherfan92:
When is shear forecast to weaken over 90L?


It is suppose to go down to around 5 kts tomorrow.
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Quoting NEwxguy:


I saw that discussion,sounds like that trough is going to be a player at some point if they get close to the conus


Strength, progression of the trough vs Strength, progression of the storms. Either one stronger, slower, faster or weaker changes the outcome.
Member Since: September 23, 2005 Posts: 14 Comments: 11269
Quoting Drakoen:
Jeff Masters says shear would be 10-20knot but shear is initialized at 8 knots and is expected to remain favorable for development in regards to


Current sat loops show outflow increasing to the SE for 'TD02'. This would support a lower shear initialization.
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Quoting mobilegirl81:
Scared like hell, lol.


Me Too Mobilegirl, me too

Taco :0)
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1363. P451
Toasty....



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12Z 8 to 10 DAY 500MB MEAN

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Is anyone else thinking 02L is looking impressive right around now?

1360. Drakoen
I appreciate your little graphics P451!

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Quoting Vortex95:
I want to be clear on this. THe G-4 planes function is to fly around 02l and then apply it to model data?

Yep.
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When is shear forecast to weaken over 90L?
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Quoting mobilegirl81:
I know this sounds like folklore, but we always have lots of squirrels and ants here in Mobile,Al and we've seen no ants(none)and squirrels are here but you never see them and they have been packing the heck out of thier nests


I had a kill a couple of ants yesterday here in Slidell. (Unfortunately, that probably means a storm coming up from the south GOM will veer right and head your way!)
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looks good.
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Quoting CaneWarning:


A major yes. A Cat 5...not that I see.


The globals show the same intensity as they always have. It is unknown whether they portray a Cat 5.
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The ants have access to better computer models than the squirrels do.
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Dvorak estimates for 02L have resumed:

Dvorak Estimates
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Quoting StormChaser81:


I think I sall that same ant in st. pete, he was packing his nest full of beer and nuts, for the upcoming storms. lol


Oh no!
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4:15 and still no HDOB's from NOAA 49
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Quoting mobilegirl81:
I know this sounds like folklore, but we always have lots of squirrels and ants here in Mobile,Al and we've seen no ants(none)and squirrels are here but you never see them and they have been packing the heck out of thier nests


the ants are in the Hebert Box installing the tunnels.
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1349. Drakoen
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Quoting CaneWarning:


Right, but I'm starting to wonder if it will be the massive Cat 5 that the models were predicting a couple of days ago.


Category 3 more likely, but this does appear prime to develop. The conditions are there, an Anti-Cyclone, ex TD-2 taking away the dry air in front of it, ect. It's just got to move away from that shear which it is expected too Tonight and into tomorrow. Because of its size, once it gets away from that shear Dry air wont be much of a problem anyways, because it will be able to moisten its environment.
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Quoting CaneWarning:


The other day I observed an ant crawling into a crack in the sidewalk in downtown Tampa. Take from that what you will...


I think I sall that same ant in st. pete, he was packing his nest full of beer and nuts, for the upcoming storms. lol
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Quoting FLHurricaneChaser:


Um, the globals have not changed the intensity of the hit on the Leewards and Puerto Rico. GFDL and HWRF continue to portray a major. And you were saying?


A major yes. A Cat 5...not that I see.
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1345. P451
Quoting Drakoen:
90L is suffering from easterly shear and dry air


That it is...





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Quoting Dropsonde:


Unlikely if it remains in the open Atlantic. But if it makes it into the Gulf and shear is what it is currently... well, probably.

The only thing really wrong with 90L right now is the easterly shear. If you look at the visible or RGB, its circulation doesn't look half bad. I have a feeling that this one is going to really kick into gear once it gets away from the shearing.


I agree. Some of the models had it as a Cat 5 east of the islands the other day. Now if it gets into the gulf that's a whole other story.
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Quoting HurricaneKyle:
More -70C cloudtops appearing on 90L, will be interesting to see if it can go over the center. Once it gets away from that shear which its forcasted to do, it won't have an issue.


Dry air is still lingering around it.
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Quoting Vortex95:


LOL okay now you are getting really specific. If both were to be named at the same time 02L would be named FIRST because it was the first to be an invest regardless of previous development it had end of story PRINT :P.


Thank you for indulging me.

Not like it's really important--if one comes my way, I'll have my own names for it, which would get me banned if I posted them here. :)
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Quoting CaneWarning:


Not the ones I'm looking at...maybe I've got a bad link.


Um, the globals have not changed the intensity of the hit on the Leewards and Puerto Rico. GFDL and HWRF continue to portray a major. And you were saying?
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so... it's interesting to see the Eastern Gulf of interest, now... i think we need to pay a little more attention to that little booger this weekend... and then in the beginning of next we can speculate more on 90L...
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Quoting CaneWarning:


Right, but I'm starting to wonder if it will be the massive Cat 5 that the models were predicting a couple of days ago.


Unlikely if it remains in the open Atlantic. But if it makes it into the Gulf and shear is what it is currently... well, probably.

The only thing really wrong with 90L right now is the easterly shear. If you look at the visible or RGB, its circulation doesn't look half bad. I have a feeling that this one is going to really kick into gear once it gets away from the shearing.
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Quoting Funkadelic:
Hey Drakoen, if td2 comes back to life and affectes Florida could it regenerate to a hurricane?


as Kevin Garnett once said
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1337. NEwxguy
Quoting nrtiwlnvragn:
HPC Extended Forecast Discussion

THE TROPICS ARE ALSO EXPECTED TO REMAIN QUITE ACTIVE.
EARLIER COORDINATION WITH THE TPC RESULTED IN DEPICTING THE
REMNANTS OF T.D NUMBER TWO REACHING FLORIDA DAYS 6/7...WHICH IS
FAIRLY CLOSE IN POSITION AND INTENSITY TO THE 00Z OPERATIONAL
ECMWF AND ECMWF ENSEMBLE MEAN. HOWEVER THE MODELS REMAIN STRONGER
DEPICTING THE TROPICAL WAVE JUST OFF THE COAST OF AFRICA...WITH A
TRACK FORECAST CLOSEST TO THE 12Z CANADIAN PREFERRED BY DAYS 6/7.
IT SHOULD BE NOTED THAT DETERMINISTIC/ENSEMBLE SPREAD REMAINS VERY
LARGE...WITH EVOLUTION OF THE CENTRAL CONUS TROUGH HAVING A DIRECT
INFLUENCE ON ANY TROPICAL WAVES THAT MOVES INTO THE WESTERN
ATLANTIC TOWARD THE END OF THE MEDIUM RANGE PERIOD. SEE TPC
DISCUSSIONS/ADVISORIES FOR MORE INFORMATION ON THIS TROPICAL
SYSTEMS.


http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html


I saw that discussion,sounds like that trough is going to be a player at some point if they get close to the conus
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More -70C cloudtops appearing on 90L, will be interesting to see if it can go over the center. Once it gets away from that shear which its forcasted to do, it won't have an issue.
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I thought the recon flight was tomorrow...is it happening now?
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About

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