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 AussieStorm:

Where?


Under Community Chat on the left side of the page.


looks like ana's north curve is comin up
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wow 456...Bill's a movin.....
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5381. hahaguy
Quoting mobilegirl81:

Is it almost as low as Ivan was?


Ivan was at 9 north at one point, not as low.
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Mobilegirl...please don't mention Ivan! That was a rough storm to ride through.
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Quoting Weather456:
before I go, the official guidance is wise to go south of the clusters. TD 3 is pretty low and showing no signs of moving north yet.

Is it almost as low as Ivan was?
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Some of the models take TD3 so far north is that the also develop it into a Cat 2/3 hurricane!! My feeling is that TD3/Bill will be no where near that strength -
Strangely enough lot of the models have been in agreement for over a day now but they have been wrong with TD currently moving WSW - one can clearly see that on the NHC Sat loops....
Quoting Funkadelic:


It is a little to far to the north though.. That has a beter chance to be a fish.


About the same latitude as pre-Ana did when it came off.
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5376. snotly
According to the 6Z GFS the hurricane is going to hit a Florida's "force field" and get defected north. Must be a government conspiracy.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/index_pcp_s_loop.shtml
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It is way too early to focus on the 5 day cone.....a good time to make sure everyone prepared with water, etc. Strength and land interaction in the short term will be the key...
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Quoting serialteg:


but its a good thing that its the most innaccurate forecast point of all ;)


I pointed that out to her also....
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Quoting Vortex95:
we have live chat but no one uses it.

Where?
Member Since: September 30, 2007 Posts: 9 Comments: 15940
before I go, the official guidance is wise to go south of the clusters. TD 3 is pretty low and showing no signs of moving north yet.
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Quoting StormJunkie:
Morning all,

Things really starting to get active. Looks like we are in the always frustrating wait and see mode for now. The islands will be the first to be impacted by either Ana, or 90L, other then that, these systems are still a long, long way off from the CONUS. As always, there will be plenty of model shifts in the coming days, for both intensity and track guidance. Wait,wait, and more waiting for now.

If you are looking for the most used forecast model, sat imagery, wind data, and other tracking sites; you can find them on this one easy to navigate page....

Quick links

See everyone later, go to go run some errands.


TD3 you mean lol.
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Quoting Orcasystems:
I was just showing SWMBO'ed where Zoo lives..I said... see this 5 day track on Ana... that green circle right at the end... thats where she lives... not good thing



but its a good thing that its the most innaccurate forecast point of all ;)
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Quoting JupiterFL:


I still believe it holds the highest probability of getting hit.
I agree with you in terms of these storms, but overall hurricane capital of the world? I think the folks in west pacific may have a tough time swallowing that.
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BBl when the models come out
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5365. Melagoo
Quoting P451:
Oh WOW - MODIS caught TD3!



WOW is right ... they have it becoming a TS by 8 tonight
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Bill almost as low as Ivan was.
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Morning all,

Things really starting to get active. Looks like we are in the always frustrating wait and see mode for now. The islands will be the first to be impacted by either Ana, or 90L, other then that, these systems are still a long, long way off from the CONUS. As always, there will be plenty of model shifts in the coming days, for both intensity and track guidance. Wait,wait, and more waiting for now.

If you are looking for the most used forecast model, sat imagery, wind data, and other tracking sites; you can find them on this one easy to navigate page....

Quick links

See everyone later, go to go run some errands.
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Quoting KBH:
may be the start of the first African depression


africa's been depressed for a while now.

no but really

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5360. breald
Quoting Vortex95:




I wonder how they come up with these numbers? North Eastern Florida has not had a hurricane hit since Dora in the 1960's. Way more than 11 years ago.
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Quoting IpswichWeatherCenter:


Its on topic, now can you stop fighting.
LOL
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Why didn't NHC put out an advisory discussion for T.D. 3?
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5356. Drakoen
GFS shows the Africa wave developing almost immediately after coming off the coast.
Member Since: October 28, 2006 Posts: 57 Comments: 30577
5355. rxse7en
Really hope someone is not going to get the 1-2 punch from Ana and Bill. Even if Ana's windfields are minimal she'll saturate the ground enough to make Bill's flooding and windfield that much worse.
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I was just showing SWMBO'ed where Zoo lives..I said... see this 5 day track on Ana... that green circle right at the end... thats where she lives... not good thing

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Quoting KBH:
may be the start of the first African depression


Wait what? LOL
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5351. KEEPEROFTHEGATE (Mod)
Quoting mobilegirl81:
Bill rapidly intensifying!
right on cue
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5329. duprk452 3:09 PM GMT on August 15, 2009
Quoting P451:
Oh WOW - MODIS caught TD3!




that looks like more than just a TD.


oh i'm sure the NHC will take into concideration that this "might be something".....extreme sarcasm
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Quoting Weather456:
The weather channel said the African disturbance shows alot of potential.

WTH? We already have Ana Td 3 and now this?


456, how is it surprising to you? I thought you were a weatherfreak ...

It's been shown on models for a while now...

Ive posted it before, but this message board epic fails in its format so information is not conveyed efficiently. A major revamp, at least to a forum-style would be GREATLY appreciated, and maybe some live chat would rule? (if someone with power and will is reading)

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5347. KBH
may be the start of the first African depression
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Quoting ALCoastGambler:
You pu tup another Poll and have the nerve to call my post off topic


Its on topic, now can you stop fighting.
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dr m dont update the blog keep it going in tell the blog hits 10,000
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leftovers 5327...you are so right...my sister works at home depot in centrlfla...it was bizarre in 2004
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5343. KEEPEROFTHEGATE (Mod)
2009 Storms
All Active Year


Atlantic
03L.THREE
02L.ANA

East Pacific
10E.GUILLERMO
09E.NINE

Central Pacific

West Pacific
94W.INVEST
91W.INVEST
01C.MAKA

Indian Ocean

Southern Hemisphere
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Link

potential water-spout generating mesocyclone S of the Keys?
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5340. jipmg
Quoting robie1conobie:
Not to overlook the near future, but the 06z surface analysis has the african wave already at 1006 mb low. Isnt that relatively low for still being over land?


well GFS is developing this into a storm shortly after it comes off africa
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5338. Drakoen
Both systems have work to do. Both have lost convection since morning.
Member Since: October 28, 2006 Posts: 57 Comments: 30577
TWC wasn't kidding when they said this is Hurricane Week!
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Quoting jasoniscoolman10:
maybe its a tropical d on land...haha.


It's happened before. Christine in 1973 formed as a Tropical Depression over Africa.
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Quoting robie1conobie:
Not to overlook the near future, but the 06z surface analysis has the african wave already at 1006 mb low. Isnt that relatively low for still being over land?


Has a good circulation, and some models are developing it. Wouldn't surprise me to see Claudette out of it.
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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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