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 extreme236:
Please let only one person post the advisory. And if you post it after someone please delete your post.


Thank you extreme...That does get annoying.
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Well, I'm out Gnite guys
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Quoting extreme236:
Please let only one person post the advisory. And if you post it after someone please delete your post.


Pfft...party pooper. :D
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Quoting CaicosRetiredSailor:


Perhaps I should rephrase this.

Can someone direct me to a source where I can find out the recent fwd speed of exTD2?

StormW
Weather 456

or any other?

thanks CRS



LINK

Just click any public advisory to get info on speed of motion
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2830. Patrap
90L Wind Field,....

1800 UTC



Member Since: July 3, 2005 Posts: 426 Comments: 128668
Quoting presslord:
Chuck....and you do a fine job...we only watch you and that Catholic dude you work with....although Lee Spann was a heck of a lot better lookin' than you two....


Appreciate it Press. I'm sure Leigh is easier on the eye compared to myself and Bill. She works at WFLA in Tampa.
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Please let only one person post the advisory. And if you post it after someone please delete your post.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting StormW:


As long as Cantore doesn't show up!
storm does it look like south florida is going to receive a hurricane gift late next week
Member Since: July 14, 2009 Posts: 0 Comments: 3022
Quoting hurricane23:


The 5 day could be atleast touching if not over southeast florida.



Hey 23,
Did you get my WU mail question wondering what you thought in regards to your comment I quoted above.
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Quoting hurricane23:


The 5 day cone could be atleast touching if not over southeast florida.

It could.

Its going to be interesting if 02L can take advantage of the OHC and low shear over the Bahamas. Its a particularly small system so it could ramp up quickly.
Member Since: June 9, 2007 Posts: 4 Comments: 15921
90L looking like a classic cape verde storm developing. It has characteristics of recent storms since 2004.
Member Since: August 31, 2008 Posts: 0 Comments: 833
Quoting hurricane23:


The 5 day cone could be atleast touching if not over southeast florida.


Or Central Florida.. I live in Northeastern/Central Florida, north of Daytona Beach.. I think I need to watch this one closely as well.
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Quoting WPBHurricane05:
First one to post the 11pm advisory for TD 2 gets a cookie.
im up for it
Areas of -70C cloud temps over 90L. An indication shear is getting weaker over 90L as it moves away from that area of shear. The Anti-cyclone is not shearing it.

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Quoting CaicosRetiredSailor:
Can someone give me data about the recent forward speed of exTD2?

Thanks.
CRS


Perhaps I should rephrase this.

Can someone direct me to a source where I can find out the recent fwd speed of exTD2?

StormW
Weather 456

or any other?

thanks CRS

Member Since: July 12, 2007 Posts: 0 Comments: 6049
Quoting sammywammybamy:
lol
LOL Tim! I got scheduled really weird this week and I'm off fri and sat instead of thurs and fri......so I can stay up late tonite :)) :))
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Quoting hurricane23:


The 5 day cone could be atleast touching if not over southeast florida.


Start the WS countdown clock :)
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Quoting extreme236:


Recent images show a burst of convection right over the center. Cold cloud tops -70C.


I need to see persistence, for convection tends to sporadically flare here and there. Nevertheless, this system will move into a less sheared area, and will have the opportunity to effectually organize. I would not be surprised if NHC classify this as a TD tonight, but it would certainly be more discreet if they postpone it for tomorrow to confirm this...
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First one to post the 11pm advisory for TD 2 gets a cookie.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Quoting Weather456:
90L is firing into the night. TD likely saturday



Yep, dunno why some people are saying that it's unimpressive and getting sheared apart when convection is blowing up right near the center, a "Tropical Depression" looking blob.
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Quoting KoritheMan:


T 1.5 is 30 mph, right? I've seen depressions (hell, TD2 was) classified with winds of only 25 kt.


Yes, but with CV systems they typically wait until 2.0 unless other information says otherwise.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Guys/Gals,

Long term lurker, but always interested in all facets of weather. Some questions for the pro's!!!

1) Does storm size or strength have a direct impact on the distance the fuji effect can be felt? What is the maximum distance for this phenoma to occur?

2) Does the size/strength also dictate which storm will rotate around which?

3) In our current scenario, which storm would be most likely to "shear" the other one? Ignorant on this...since we have an anticyclone tracking with one, does it give our larger storm a better chance at shearing the other?

4) Does anyone have a rule of thumb they use for jogs to the s/wsw before Conus really needs to be concerned? I'm assuming there's a historical average for the degree of turn a storm can take...in other words is there a point via Long/Lat that it becomes nearly impossible to avoid land interaction?
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Quoting willdunc79:
TD 2 renamed at 11pm advisory and 90L TD #3 by Saturday night @ latest JMHO.


Agreed.
Member Since: March 7, 2007 Posts: 585 Comments: 20854
Quoting extreme236:


I think its lack of TD status would have more to do with the T1.5. A broader circulation wouldn't be unexpected with a large cyclone.


T 1.5 is 30 mph, right? I've seen depressions (hell, TD2 was) classified with winds of only 25 kt.
Member Since: March 7, 2007 Posts: 585 Comments: 20854
72 hour surface forecast.

NHC says due west with 90L.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Looks like the anticyclone that was supposed to save it from shear is currently shearing it. Irony.

Member Since: June 9, 2007 Posts: 4 Comments: 15921
Quoting StormW:
Good evening!

2 good preparedness brochures


UNLEASHING NATURE'S FURY


AGAINST THE WIND


Thank You
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Quoting BajaALemt:
00z NAM's starting to come out.....GFS shouldnt be too far behind


Hey Baja....you working nights or days now.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
90L is firing into the night. TD likely saturday

Member Since: July 24, 2005 Posts: 407 Comments: 19076
TD 2 renamed at 11pm advisory and 90L TD #3 by Saturday night @ latest JMHO.
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Quoting Stormchaser2007:


11pm.


The 5 day cone could be atleast touching if not over southeast florida.
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Quoting cchsweatherman:


Even though it may be broad due to the sheer size, the circulation most importantly is CLOSED. I will admit the satellite presentation is quite unusual, more typical of a Pacific system, but with all the data available and given the fact convection has been building and persisting over the circulation center, it has all the factors in my mind to become a tropical depression. Of course, thats the NHC's call so I could be wrong.


Western side still looks a bit elongated, though, indicative of some easterly shear over the area.
Member Since: March 7, 2007 Posts: 585 Comments: 20854
I wonder if we'll get our first blog crash this weekend.....
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2799. 7544
hmm so if the nhc does call td2 again will we see a differnt track , cone then it was yesterday this time further west ?
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Quoting CycloneOz:
After weeks of tropical regressions
Tonight there are twin depressions
In this nameless condition
These two may have ambition
To unleash some TC aggressions!


Word!
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Chuck....and you do a fine job...we only watch you and that Catholic dude you work with....although Lee Spann was a heck of a lot better lookin' than you two....
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90L starting to make me a believer. Latest IR image is impressive as convection is exploding over the center.

Link
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Quoting canesrule1:
No


Already posted.
Member Since: March 19, 2009 Posts: 0 Comments: 1421
Quoting rareaire:
I owed you that one Tampa, but the rest of them are all you buddy! lol


Nothing gay here or anything but thanks alot. LOVE ya man.....ROFLMAO
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Quoting futuremet:


The primary convection mass displaced well west of the center. The structure of this system is mediocre at best, and I think it is more reasonable to upgrade this tomorrow.


Recent images show a burst of convection right over the center. Cold cloud tops -70C.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
After weeks of tropical regressions
Tonight there are twin depressions
In this nameless condition
These two may have ambition
To unleash some TC aggressions!
Member Since: August 26, 2006 Posts: 10 Comments: 3753
Quoting Weather456:


no one is getting worried, just an obs that was confirmed.
worried isn't the right word, more like nothing to monitor.
-80C cloudtops are starting to show on 90L, right over the COC.
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Quoting KoritheMan:


That is to be expected with large systems with broad circulations like 90L. These things take time to consolidate.


I think its lack of TD status would have more to do with the T1.5. A broader circulation wouldn't be unexpected with a large cyclone.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting cchsweatherman:
To be honest, I don't see any reason besides waiting for further persistence to not classify Invest 90L as a tropical depression at 11PM.


The primary convection mass displaced well west of the center. The structure of this system is mediocre at best, and I think it is more reasonable to upgrade this tomorrow.
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Definitely feeling some excitement in the Atlantic Ocean tonight... =)
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Quoting BajaALemt:
00z NAM's starting to come out.....GFS shouldnt be too far behind

Not for a good couple of hours will we get the longer-range plots. The full GFS schedule here: http://www.nco.ncep.noaa.gov/pmb/nwprod/prodstat_new/prdst_00_UTC_GFS.html
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting KoritheMan:


Circulation is still broad.


Even though it may be broad due to the sheer size, the circulation most importantly is CLOSED. I will admit the satellite presentation is quite unusual, more typical of a Pacific system, but with all the data available and given the fact convection has been building and persisting over the circulation center, it has all the factors in my mind to become a tropical depression. Of course, thats the NHC's call so I could be wrong.
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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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