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:
Ana advisory coming out. Still a TS.

Link plz
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...TROPICAL DEPRESSION THREE FORMS IN THE EASTERN ATLANTIC...
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BULLETIN
TROPICAL STORM ANA ADVISORY NUMBER 14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
1100 AM AST SAT AUG 15 2009

...ANA...PRONOUNCED AH-NA...MOVING QUICKLY WESTWARD WITH LITTLE
CHANGE IN STRENGTH...

INTERESTS IN THE LEEWARD ISLANDS...THE VIRGIN ISLANDS...AND PUERTO
RICO SHOULD MONITOR THE PROGRESS OF ANA. A TROPICAL STORM WATCH MAY
BE REQUIRED FOR PORTIONS OF THE LEEWARD ISLANDS LATER TODAY.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA
OUTSIDE OF THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR NATIONAL METEOROLOGICAL SERVICE.

AT 1100 AM AST...1500 UTC...THE CENTER OF TROPICAL STORM ANA WAS
LOCATED NEAR LATITUDE 14.3 NORTH...LONGITUDE 48.3 WEST OR ABOUT
920 MILES...1480 KM...EAST OF THE LEEWARD ISLANDS.

ANA IS MOVING TOWARD THE WEST NEAR 16 MPH...26 KM/HR. A TURN TOWARD
THE WEST-NORTHWEST IS EXPECTED DURING THE NEXT COUPLE OF DAYS.
THIS MOTION COULD BRING THE CENTER OF ANA NEAR THE LEEWARD ISLANDS
ON MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/HR...WITH HIGHER
GUSTS. SOME SLOW STRENGTHENING IS FORECAST DURING THE NEXT
48 HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB...29.68 INCHES.

...SUMMARY OF 1100 AM AST INFORMATION...
LOCATION...14.3N 48.3W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1005 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
500 PM AST.

$$
FORECASTER BEVEN

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Quoting kmanislander:


I just took a look at that.There are two ULLs at work, one in the NW GOM and another in the NW Caribbean. Over the keys you have what's left of the N end of a Twave that is moving W at this time through the NW Caribbean. The interaction of all these features is creating a chaotic situation with rain showers all around.

I do not see anything suggesting that a surface feature of any concern is developing out there at this time.

Gotta go now. Catch you all later.


Just checked all the Florida Keys buoys. No west or even north winds. Apparantly, no or a very week surface low at this time.

NOAA NDBC
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5129. Drakoen
Quoting TerraNova:
Hey Drak/W456, a question...would you call that band of low level cloud cover bridging together both the centers of Ana and 90L a form of Fujiwara interaction? According to the Wikipedia article two storms need to be within 900 miles of each other for the effect to occur; 90L's core is about 935 miles from Ana, not too much more than 900 especially considering 90L's large size.


At the present time I do not see that
Member Since: October 28, 2006 Posts: 57 Comments: 30205
Quoting CJ5:


I disagree, Cane. I don't see anything in the current steering maps that would push her anywhere but W.
That is what Local10, one of my local news stations said.
In fact Drakoen, the storms seem to be feeding off of the moister ITCZ proximity and the warmer SST boundaries present to the west for Ana and to the south for 90L. Not only that, but they have maintained westward movement in favor of the warm waters now.
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Quoting Ameister12:
Poll time!!!

What intensity do you think 03L is going to peak out at?
A)Tropical Storm
B)Cat. 1
C)Cat. 2
D)Cat. 3
E)Cat. 4
F)Cat. 5



Cat two if it survives
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...ANA...PRONOUNCED AH-NA...MOVING QUICKLY WESTWARD WITH LITTLE
CHANGE IN STRENGTH.

...SUMMARY OF 1100 AM AST INFORMATION...
LOCATION...14.3N 48.3W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1005 MB
Member Since: July 24, 2005 Posts: 407 Comments: 19076
...ANA...PRONOUNCED AH-NA...MOVING QUICKLY WESTWARD WITH LITTLE CHANGE IN STRENGTH...

Didn't know that, hmmm.
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Quoting leftovers:
did anyone know of a major making landfall e cen florida? a fellow blogger and i researched this and we couldnot find one ever
Hurricane Eloise--A powerful hurricane that formed in September, 1975, Eloise was a Category Three Hurricane with sustained winds of 125 mph, and gusts of up to 156 mph. It produced a 12 to 16 foot storm surge along the Florida Coast from Ft. Walton Beach to Panama City, Florida. With a minimum central pressure of 28.20 inches, Eloise was the first major hurricane to make a direct hit on this area in the 20th century, and caused some $1 billion dollars in damage as well as 21 deaths.
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Quoting Funkadelic:


Drakoen, as the XTRP model shows, 90L is still moving W/WSW. When is this movement expected to stop?


XTRP is not a model
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Should see TD3 on there momentarily.
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come on TAZ that was a typo and ANA is no where nera 10 deg
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"Bill" to be is diving towards the sw. Was that predicted?
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aiming for southern tip of FL.

OUTLOOK VALID 20/1200Z 25.0N 80.0W
MAX WIND 60 KT...GUSTS 75 KT.
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Quoting Ameister12:
Poll time!!!

What intensity do you think 03L is going to peak out at?
A)Tropical Storm
B)Cat. 1
C)Cat. 2
D)Cat. 3
E)Cat. 4
F)Cat. 5

I hope for A or B but think maybe D or E
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This came true, as the system's remnants regenerated into a tropical depression early on August 15 and shortly strengthened into the first tropical storm of the season. Ana and another area of low pressure to its east were encountering wind shear. The wind shear has now diminished, allowing for slow strengthening of both storms.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
I think when the convection on the sw side of td3 gets rapped around the top of the system it is on then.
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5114. CJ5
Quoting canesrule1:
no because Ana is strengthening.


I disagree, Cane. I don't see anything in the current steering maps that would push her anywhere but W.
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Ana advisory coming out. Still a TS.
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Ana's the same.

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5111. Skyepony (Mod)
Quoting zoomiami:
This is for the model experts: now that they have a depression to initialize with, what runs of the models will start to have the more accurate tracks?


Model Performance Statistics for AL022009
Average Error (nm) for core models
model Error Trend 24hr Error 48hr Error 72hr Error Day 4 Error Day 5 Error
OFCL DECREASING 38.5 59.9 113.9 -1 -1
MM5A INCREASING 71.5 85.9 92.8 109.6 -1
GFDL DECREASING 79.6 140.1 251.2 373.1 406.2
KHRM DECREASING 82.4 137.8 189.1 286 -1
LBAR INCREASING 98.3 237 467.1 745.1 1022.8
BAMD CONSTANT 98.8 201.3 355.3 548.3 755.3
HWRF DECREASING 99.7 123.7 259.6 392.3 377
MM5E INCREASING 113.4 169.2 183.9 133.1 -1
MM5B INCREASING 118.7 179.2 218.8 257.8 -1

For all model comparision check here.
Member Since: August 10, 2005 Posts: 162 Comments: 37820
Quoting Ameister12:
Poll time!!!

What intensity do you think 03L is going to peak out at?
A)Tropical Storm
B)Cat. 1
C)Cat. 2
D)Cat. 3
E)Cat. 4
F)Cat. 5
CAT 5
Quoting amd:


pressures are high, thunderstorms are being caused by interaction between upper level low and tropical wave.

unless that upper level low disappears, convergence will not be there to develop a surface low


Thank you, I appreciate the time you took to post a reasonable explanation. I am also giving you one of my very rare, and highly coveted "+"s on your post.
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Quoting sammywammybamy:



I Just woke up... and it still hurts... So whats up with Td2 .. I mean Ana?
Hey what up? alright u r designated to be the only person to post both advisories.
Quoting Drakoen:
I don't see the NHC making a dramatic shift to the forecast track until they see some 12z runs


Thanks Drak
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Quoting stoormfury:
456
i am beginning to suspect that 90L will not make that early forecast turn this is a matter of concern down the road



its TD 3
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Poll time!!!

What intensity do you think 03L is going to peak out at?

A)Tropical Storm
B)Cat. 1
C)Cat. 2
D)Cat. 3
E)Cat. 4
F)Cat. 5
Member Since: Posts: Comments:
5103. ssmate
Quoting stillwaiting:
90l=TD3 and has a good chance of becoming a hurricane in the next 24hrs,imo


I agree. It's looking mighty impressive.
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5102. amd
Quoting CycloneOz:


Why for heaven's sake? Is it because forecaster Bevens does not see any model support for it?

Please...anyone...someone...why?


pressures are high, thunderstorms are being caused by interaction between upper level low and tropical wave.

unless that upper level low disappears, convergence will not be there to develop a surface low
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Quoting Cotillion:
First lot of advisories for Ana/TD3 should be here in roughly 15 minutes.

Don't all post at once...

A nice scenario: Don't post them here at all.
I think we all know where to get it.
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Hey Drak/W456, a question...would you call that band of low level cloud cover bridging together both the centers of Ana and 90L a form of Fujiwara interaction? According to the Wikipedia article two storms need to be within 900 miles of each other for the effect to occur; 90L's core is about 935 miles from Ana, not too much more than 900 especially considering 90L's large size.
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Bil might skip depression status.
Member Since: August 31, 2008 Posts: 0 Comments: 833
5098. Drakoen
I don't see the NHC making a dramatic shift to the forecast track until they see some 12z runs
Member Since: October 28, 2006 Posts: 57 Comments: 30205
456
i am beginning to suspect that 90L will not make that early forecast turn this is a matter of concern down the road
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5096. Drakoen
There is no evidence on water vapor imagery or MIMIC-TPW that suggests either system is robbing energy from the other.
Member Since: October 28, 2006 Posts: 57 Comments: 30205
Quoting AussieStorm:

Can we designate 1 person to post the advisory so there isn't 10 oh it
yea, WHERE IS SAMMY???lol
90l=TD3 and has a good chance of becoming a hurricane in the next 24hrs,imo
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Quoting stoormfury:
99L continues to parallel the 10 deg lat line



99L??? 99L is long gone 99L is now TD 2/anna
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Quoting Weather456:


Quoting canesrule1:
Look at the umbilical cord, lol.

what do you call it fugwara or something like that that is what it look like
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5089. tbrett
Weather456

I seen this earlier, what are your thoughts. Not looking good for N leewards next week.Link
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Quoting mobilegirl81:
Both systems seem to be skimming southerly. Models shoot west and wont go back as far east.

No northward component is evident
Member Since: August 31, 2008 Posts: 0 Comments: 833
Quoting truecajun:
morning everyone. any thoughts on the wave near cuba? is it something to keep an eye on?
Here is the key West forecast discussion.....AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
948 AM EDT SAT AUG 15 2009

.DISCUSSION...
.CURRENTLY...
THE NORTHERN PORTION OF A TROPICAL WAVE EXTENDING FROM THE FLORIDA
STRAITS INTO THE CARIBBEAN IS CURRENTLY MOVING WESTWARD THROUGH THE
FLORIDA STRAITS AND IS BEGINNING TO IMPACT THE MIDDLE AND UPPER
KEYS...AND WILL IMPACT THE LOWER KEYS WITHING THE NEXT FEW HOURS. A
CONVECTIVE MASS IN THE STRAITS EAST OF THE KEYS IS EVIDENT ON KBYX
RADAR...WITH A BROAD MID LEVEL CIRCULATION DETECTABLE FROM AROUND
10KFT THROUGH 25KFT. THE APPROXIMATE MAXIMUM OF THE CIRCULATION IS
AROUND 700MB...AND THERE IS ALSO A WEAK CIRCULATION DETECTED FROM
AROUND 5KFT TO THE SURFACE. SURFACE WINDS AT ISLAND STATIONS ALONG
THE KEYS HAVE BEEN MORE OF LESS SOUTHEAST FROM 5 TO 10 KNOTS OVER THE
PAST FEW HOURS...WITH CMAN STATIONS ALONG THE REEF A COUPLE OF KNOTS
BELOW 10 KNOTS WITH GUSTS NEAR 15 KNOTS. MOLASSES REEF...WHICH IS
NEAREST THE CONVECTION...HAS REGISTERED THE HIGHEST WINDS THUS FAR
WITH SUSTAINED WINDS OF 16 KNOTS AND GUSTS OF 18 KNOTS.Link I would keep an eye on it. The Water temps are plenty warm,just my amateur opinion... ok i am back to lurking........
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Funkadelic,

Especially if there are low amounts of showers and thunderstorms leading up to the path into the Bahamas. The best time for these storms to organize is when they look like they have less clouds. Then there are warmer temperatures on the sea surface and the former boundaries are still present to start the storms better. Overall, these storms have already surprised most. The season looked to be waning and it started late, but here we are going into a time of warm temperatures and it's only August 15th. What a difference a day makes!
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Wow! 102 pages I knew it would be a zoo in here. Looks like this season just came out of stealth mode.
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feeding outflow - fujiwara - clarification?
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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.