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 jipmg:


monday??


mid next week. sorry Monday was the drop time
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Just refreshed the models on Google Earth now 90L is a FISH? is it me or these models have no clue what that storm will do.
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Do you have this models? Pls, can you post them here? :)
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3931. jipmg
Quoting WeafhermanNimmy:


You dont determine it by pressure. I noticed in their tropical discussion the QuickScat...is what they observe the most. That was why when TD 2 formed last week it wasnt upgraded. It showed 30 kts. winds.


when pressure drops it takes a while for the wind to respond, but it does go up
3930. 7544
Quoting weatherblog:
FINALLY!

1-0-0


lol was waiting for that one
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Quoting jipmg:
pressures are at 995mb, how can it not be ana
You dont determine it by pressure. I noticed in their tropical discussion the QuickScat...is what they observe the most. That was why when TD 2 formed last week it wasnt upgraded. It showed 30 kts. winds.
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3928. jipmg
Quoting Weather456:
Good Morning, Antiguia said if Tf2 gets too close will issue advisories by Monday.


monday??
What the hell, look at 90L, that is TD 3 for sure

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FINALLY!

1-0-0
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Quoting leftovers:
looking for the gulf circle and the cuba circle to consolidate into one. after that will it move wnw? doubt we will see any storms until recon confirms it


Do you have your own weather center?
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Good Morning, Antiguia said if Tf2 gets too close will issue advisories by mid Next week.
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3921. jipmg
pressures are at 995mb, how can it not be ana
For Crying out loud...its not Ana yet..so dont say that!
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Quoting 7544:


its over look now


Thanks! Checking now...
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3918. jipmg
good outflow showing up on ana and td3, well im going to sleep
Quoting 7544:
thats right so now anna will be on the next nhc update or speacail update

90L.INVEST
02L.ANA


Nope! I doubt it! QuickScat winds dont support it! Plus if it's a special advisory they should have already made the advisory.
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Looking at latest sat pic of TD2 at 615UTC, I think the center of circ has now completely moved under strong convection on its east side. The convection around 90L's center is waning a bit but is remaining constant over its center. I think we have a TS and a TD by 5am and really need to watch the Gulf system. Of course, I am not a 40 year vet on the nuances of tropical cyclones either. Nighty, night.
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Friends, i am a student here, but how is that possible? Navy have an information but is NOT official until NHC confirm that? It's just about the satellite details?
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3914. KEEPEROFTHEGATE (Mod)
Quoting Patrap:
90L still a Invest,but that will change most likely the next 12 to 24
by afternoon pat we should have td 03l from 90l
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3912. Patrap
TMI
08/15 0332 Z, TRMM

0041

08/15 1146 Z, TRMM

0573



Member Since: July 3, 2005 Posts: 426 Comments: 128764
3911. 7544
Quoting druseljic:
We should be getting close the end of the blackout, right?


its over look now
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We should be getting close the end of the blackout, right?
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3909. 7544
thats right so now anna will be on the next nhc update or speacail update

90L.INVEST
02L.ANA
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02L.ANA, TRACK_VIS, 15 AUG 2009 0615Z

OMG!!!
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3907. Patrap
90L still a Invest,but that will change most likely the next 12 to 24
Member Since: July 3, 2005 Posts: 426 Comments: 128764
Quoting jipmg:
so we have ana but no TD 3?


No it's not Ana yet until the NHC declares it but based on the QuickSCAT it shouldnt be!
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I dont think it will be Ana because the QuickScat doesnt show winds of 30 knots and it came out like 10 mins ago....I think it's an error!
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3904. KEEPEROFTHEGATE (Mod)
latest image 615 utc



02L/TS/ANA
MARK
14.1N46.3W
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Thx keeper! how is possible NHC does not give any special feature for that?
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3901. jipmg
so we have ana but no TD 3?
3899. Patrap
The First Atlantic Tropical Storm is Born for 2009

Atlantic
green ball icon90L.INVEST
green ball icon02L.ANA

NAVY PAGE
Member Since: July 3, 2005 Posts: 426 Comments: 128764
3898. KEEPEROFTHEGATE (Mod)
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I was there just few min ago and i dont see any confirmation of "Anna"
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3896. KEEPEROFTHEGATE (Mod)
2009 Storms
All Active Year


Atlantic
91L.INVEST
90L.INVEST
02L.ANA

East Pacific
10E.GUILLERMO
09E.NINE

Central Pacific

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

Indian Ocean

Southern Hemisp
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3894. Patrap

Atlantic
green ball icon90L.INVEST
green ball icon02L.ANA

NAVY PAGE


Member Since: July 3, 2005 Posts: 426 Comments: 128764
Quoting leftovers:
your own personal hurricane center?


No it's on the navy site
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Quoting washingaway:
it's ana on the navy site now


Let see...but I dont think so!
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3890. KEEPEROFTHEGATE (Mod)
Quoting washingaway:
we have Anna now
not official but iam expecting it at 5 am update
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it's ana on the navy site now
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Is confirmed?
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6:52 AM UTC QuickSCAT in! Shows 30 knot winds, north of the low, still.

Guys I don't think this will be upgraded to Ana...@ 5 AM!
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Link
Atlantic is boiling!
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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.