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 thought the recon flight was tomorrow...is it happening now?
Member Since: Posts: Comments:
1333. Drakoen
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


The prefer the Canadian which is no surprise given the ECMWF is still taking this thing out to sea they want to find a balance and the CMC provides that. Depicting a trough as well as a ridge.
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90L may not look the best but convection still continues to build well in DMIN. Maintaining convection is the most important thing and 90L is doing so admirably. Once it gets out of the shear and dry air all systems are go.
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Google Earth says there is no flight to track
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Quoting wally12:
Just a hello from Alberta Canada!
Been lurking since before Katrina..
I plan on sailing down to your Gulf area later this fall and am looking forward to that a LOT!
This is a really great informative and important! blog and good fun just following along!

(I hope the font isn't as big as it's showing in this box..sorry if it is.)


You sailing out of Calgary? *wink*
Member Since: Posts: Comments:
1328. Drakoen
Quoting Funkadelic:
Hey Drakoen, if td2 comes back to life and affectes Florida could it regenerate to a hurricane?


It's too early to say that but the models that do regenerate it do take it up to a hurricane in the Bahamas.
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Scared like hell, lol.
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1326. 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 02L.


TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
V (KT) NO LAND 25 27 30 33 37 43 51 57 65 68 71 73 76
V (KT) LAND 25 27 30 33 37 43 51 57 65 68 71 73 76
V (KT) LGE mod 25 26 27 29 31 36 41 49 56 66 73 77 80

SHEAR (KT) 8 10 4 2 4 7 1 10 3 13 11 14 5
SHEAR DIR 118 134 168 155 109 242 351 276 81 250 252 269 335
SST (C) 26.7 26.6 26.6 26.7 26.9 27.4 28.0 28.3 28.4 28.5 28.4 28.8 29.5
POT. INT. (KT) 122 120 121 122 125 132 140 145 146 147 145 150 161
ADJ. POT. INT. 118 115 116 119 122 132 142 148 147 146 140 141 149
200 MB T (C) -52.9 -52.9 -53.1 -53.2 -53.0 -53.3 -53.6 -53.6 -53.8 -53.6 -53.8 -54.0 -54.0
TH_E DEV (C) 8 8 8 8 8 9 10 10 11 12 12 12 14
700-500 MB RH 55 59 56 55 56 53 51 49 51 46 48 47 45
GFS VTEX (KT) 9 9 LOST LOST LOST LOST LOST LOST LOST LOST LOST LOST LOST
850 MB ENV VOR 66 69 68 62 57 40 15 -3 -14 -50 -68 -93 -109
200 MB DIV 0 6 7 -10 -25 1 -12 -4 14 8 6 -9 22
LAND (KM) 1481 1428 1374 1331 1304 1238 978 675 257 220 233 264 240
LAT (DEG N) 14.7 14.9 15.1 15.5 15.9 16.6 17.5 18.3 19.5 20.6 21.9 23.1 24.0
LONG(DEG W) 43.2 44.3 45.3 46.7 48.0 51.2 55.1 59.3 63.6 67.6 71.3 74.4 77.0
STM SPEED (KT) 13 10 12 14 14 18 19 21 20 19 17 14 13
HEAT CONTENT 5 6 6 7 13 31 47 60 51 52 22 63 83
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1325. Patrap
Little By Little,everything channges
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Quoting iluvjess:
Link to Cuban Radar?


Here's the site, but it is a blank page at the moment (on my computer at least).

Cuba Radar
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Quoting FLHurricaneChaser:


Umm the models are still showing that


Not the ones I'm looking at...maybe I've got a bad link.
Member Since: Posts: Comments:
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
Member Since: September 23, 2005 Posts: 14 Comments: 10923
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 other day I observed an ant crawling into a crack in the sidewalk in downtown Tampa. Take from that what you will...
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Looks like 90L is trying to build convection around the center.
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1317. Drakoen
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?


Yes. They should be put into the 00z runs.
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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.


Umm the models are still showing that
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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
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1314. cg2916
90L looks pretty impressive as of late. It seems we may get TD 3 soon, once the LLC closes.
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Quoting wally12:
Just a hello from Alberta Canada!
Been lurking since before Katrina..
I plan on sailing down to your Gulf area later this fall and am looking forward to that a LOT!
This is a really great informative and important! blog and good fun just following along!

(I hope the font isn't as big as it's showing in this box..sorry if it is.)
Well welcome aboard, hope you like it.
Member Since: Posts: Comments:
1312. slavp
Quoting cg2916:
How come the recon flight data isn't showing up on Google Earth?
Only been in the air 8 minutes
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The 18z statisticals are out...basically holding steady.
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Quoting Vortex95:


02l would be named first because it was there first.


02L was the first to be a tropical cyclone, certainly (with 90L yet to become one). When you say "there first" do you mean as a tropical cyclone or an invest?

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1308. Drakoen
Good low level structure and low level spirals:
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It's not a standard recon flight, that might be why there's not data showing up.
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1306. Patrap
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Quoting weatherboykris:


Most storms don't roll of the coast and start going immediately. It takes awhile. I remember Frances in particular. But once they start intensifying, they do it FAST. So don't take the fact that this one hasn't done anything yet, to mean that it won't. Keep in mind how bad it looked this time yesterday, and how it blew up overnight. Tonight should be interesting to watch.


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.
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1304. cg2916
How come the recon flight data isn't showing up on Google Earth?
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1303. Drakoen
02L is holding its own and once it gets past 50W I cannot see why it could not develop.
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1302. wally12
Just a hello from Alberta Canada!
Been lurking since before Katrina..
I plan on sailing down to your Gulf area later this fall and am looking forward to that a LOT!
This is a really great informative and important! blog and good fun just following along!

Member Since: Posts: Comments:
1301. WxLogic
Quoting OSUWXGUY:


Ha Ha. I was trying to turn your comment into something dirty, and sadly I've got nothing...


lmao!!!
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It did seem VERY premature for everyone saying 90L was going to be "the one" when it didn't even have a circulation... Opportunities are not always taken, especially when Mother Nature is behind it.
1299. 786
Caribbean bound for now as expected...the models will shift North again, they will mainly be PR/FL/Bermuda bound again and then again we will see them shift perhaps even further S into the Caribbean and then shift again to only God knows where.
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Quoting CaneWarning:


I am.


Most storms don't roll of the coast and start going immediately. It takes awhile. I remember Frances in particular. But once they start intensifying, they do it FAST. So don't take the fact that this one hasn't done anything yet, to mean that it won't. Keep in mind how bad it looked this time yesterday, and how it blew up overnight. Tonight should be interesting to watch.
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All ready 10% increases in prices at Lowes and Home Depot.Do they know something we dont?
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1296. hahaguy
.
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1295. 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!*
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Quoting WxLogic:


Nice cross section...


Ha Ha. I was trying to turn your comment into something dirty, and sadly I've got nothing...
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1292. ackee
see few models run shifting further south when reach near the NE carrb
Member Since: July 15, 2008 Posts: 0 Comments: 1355
Quoting weatherboykris:


I was actually directing it at WS...but there are several people to whom it could be applied. Look, my point is is that if the Euro is telling me one things, and the dime a dozen statistical models(such as the BAMs, LBAR, etc.) are telling me something else, well, based on my years of (amatuer) experience, it's a no-brainer which one I'll lean towards. In this case, with the GFS, GFDL, HWRF and other high end models siding with the statisticals, I think that the more southern track is correct. I'm just making a point that you shouldn't totally disregard one of the best models out there just cause u don't like it.
no i don't like, it because it has been forecasting an early curve, but then i was reading that the trough that was supposed to curve it was weakening and that model still had it curving around the the Dominican Republic, so i discarded it and i thought the model was rather useless, and yes i know this model is a very good model because i have seen it be correct multiple times over that past several years.
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All i'm saying is that the models showed a monster blowing up easy as pie with perfect conditions for this to occur now we are snapping more back to reality
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Quoting Drakoen:


02L gets named first


Sorry, I was looking for a reason as well and didn't ask for it.
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Quoting Patrap:
Latest SAL Split-Window


02L....finally I can breathe...cough.
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Quoting louisianaboy444:
90L is suffering from easterly shear and dry air

Are you beginning to believe this storm might not be the big monster it was hyped up to be


I am.
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Quoting Camellia1356:
If 02L and 90L grow to TS at the same time, how are the names allocated?


Pretty sure TD2 would get the name.
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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.