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

By: Dr. Jeff Masters , 2:02 PM GMT en Agosto 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 Weather456:
another F5 session later this morning. The little that are still fucntion after last night late advisory.


That was too funny...
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Quoting Weather456:
another F5 session later this morning. The little that are still fucntion after last night late advisory.


Did that advisory ever come in? lol... I fell asleep waiting.
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90L (really just an invest? depression at 11am...?)


Are there example of past storms in compare to 90L? Especialy orginateing from the african wave train.

Also is there a image with the new african wave and Ana and 90L(bill)?

Good Morning
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I am reading people talking about 90L moving a bit S of W... look at the HWRF and other models... they show that happening for just a bit... HWRF also shows it moving more NW and then back W around Bahamas...
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4430. JRRP
Quoting CycloneOz:
Looking at the 5-day cone and comparing them to the latest imagery animations...this anA (and the other one also) are still moving WSW.

So the models are going to shift again and so will the cone.

I woke up in a bad mood.

i agree
Link
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4429. KBH
Quoting kmanhurricaneman:
i will stick to my guns i believe these storms are gonna be caribbean storms, so everyone in the caribbean especially nw keep on top of this.

Kman, than may be true, but when the pass the chain of islands they grow in GOM, so every one better watch out
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Quoting Weather456:
another F5 session later this morning. The little that are still fucntion after last night late advisory.
lol
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this in

15/1145 UTC 14.3N 47.2W T2.0/2.5 ANA -- Atlantic
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another F5 session later this morning. The little that are still fucntion after last night late advisory.
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Thank You Ike
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Quoting jipmg:


Ana is moving straight west, and our low is moving west or wsw (which is forecasted)


agree
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4422. ackee
90L continue a slight WSW movement wonder if this will change the GFS and other models next runs ?
Member Since: Julio 15, 2008 Posts: 0 Comments: 1376
Quoting caneluver:
Does it look like 90L will miss the conus and be a fish storm?



90L is way to faar S too be a fish storm
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I have been watching that since yesterday, clearly has rotation and has plenty of moisture and warmth. NHC puts it at low probability, however the GOM is like hot soup, should be interesting, gotta check the shear.
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Quoting Funkadelic:


Dont underestimate ANA, she is very small so once she is by the bahamas streghtning can happen rather fast.


yea, read the post just before yours, i doubt the TCHP will allow ana to amount to little.
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i will stick to my guns i believe these storms are gonna be caribbean storms, so everyone in the caribbean especially nw keep on top of this.
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Quoting WeatherStudent:


Morning pressy. L(


Umm...don't look at the NHC website. :D
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4414. IKE
Quoting tharpgomex:
good morning all...I live on the Florida Panhandle...Panama City.. will this wave bring my area some rain?


Yes....

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Just to let everyone know but, the NAM has nearly a Depression forming in the GOM today and heading toward the Panhandle area. Told you all last nite to watch this area!

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There is also another burst occuring on Ana, I doubt TCHP will let ana amount to little

Double Trouble: Ana forms; TD 3 developing
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Quoting WeatherStudent:


G'morning StormW. Any brief thoughts on the potential intensity forecast for Ana in the long halt?

why should it have to halt?
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Quoting TampaSpin:
How can 90L not be a Depression.....WOW its looking very healthy..


They are going to skip the depression jargon and go straight to calling it Bill I reckon.
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Quoting sailfish01:
Is it just me or is the northen end of the wave SE of Fl beginning to rotate. Could that system become better organized so close to land? Could it pass into the GOM and blow up? Weather for the keys: A large area of moderate rainfall with embedded scattered showers and isolated thunderstorms will impact almost all of the offshore waters 25 to 60 nm offshore of the Upper Keys. The strongest showers and storms will produce wind gusts near 30 knots...heavy downpours accompanied by visibility less than 2 nm...and occasional cloud to water lightning strikes.

Noticed that myself, and watching it as well as with the other more defined storms.
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Looking at the 5-day cone and comparing them to the latest imagery animations...this anA (and the other one also) are still moving WSW.

So the models are going to shift again and so will the cone.

I woke up in a bad mood.
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90L and Ana are extremely impressive this morning.
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4402. jipmg
Quoting serialteg:


Both seem to be jogging southward, I reckon!


Ana is moving straight west, and our low is moving west or wsw (which is forecasted)
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4401. ackee
Quoting serialteg:


Both seem to be jogging southward, I reckon!
agree
Member Since: Julio 15, 2008 Posts: 0 Comments: 1376
Quoting StormW:


They're all with KerryinNOLA and stormno signing up for Meteorology 101 when school starts back.
Morning all I have awoke from my slumber. StormW that was funny. Looks like the Angry Bear has come out of its Summer Hibernation
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Quoting Weather456:


12Z, the earliest hurricane model is the GFS around 11:30 am today, then others follow. Some other models comes out before the GFS but other than the NAM the GFS is 1st.


Don't forget the human model at 1500Z.
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Quoting Weather456:
wow just wow



Both seem to be jogging southward, I reckon!
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4395. jipmg
you know that wave south of SFLA headed into the gulf is something to watch...
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good morning all...I live on the Florida Panhandle...Panama City.. will this wave bring my area some rain?
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Quoting Weather456:
wow just wow




...that kinda sums it all up...
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Quoting pensacolastorm:
When do the next run of the models come out?


12Z, the earliest hurricane model is the GFS around 11:30 am today, then others follow. Some other models comes out before the GFS but other than the NAM the GFS is 1st.
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4390. JRRP
Quoting Weather456:
wow just wow


90L looks like moving south
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Quoting Weather456:
wow just wow



Incredible isn't it we make it until August 15 with no named storms and now we have the potential for two to form in one day. Season's ramping up real quickly as we gradually near September.
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Alright you little buzz saw wannabee...that's enough.

Stay as a TS, e no mas!
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Quoting dcoaster:


Yikes, again.


i see that gfs run dissipates ana...
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all so now that we have a name storm this is when the Admin starts baning


so i would stay on key


so no poting off key photos

no personal attacks

and no bickering

follow the rules this find and you wont be ban



olny stay with posting material relevant to the discussion of tropical weather, or the topic of the blog entry itself.
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4385. ackee
THE HIGH is the key telling us where 90L and TSAna will go
Member Since: Julio 15, 2008 Posts: 0 Comments: 1376
90L is also displaying banding features
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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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