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 nrtiwlnvragn:


Goes out to 126 hrs, its displayed at the top of the screen.
yeah, sorry about that. I saw it and forgot to delete the post.
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A tropical storm followed by a hurricane



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4282. IKE
Quoting ALCoastGambler:
How many hours out is that nrt?


Seems right in-line w/NOGAPS.

Anyone have a 00Z UKMET run?
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Quoting ALCoastGambler:
How many hours out is that nrt?


Goes out to 126 hrs, its displayed at the top of the screen.
Member Since: September 23, 2005 Posts: 13 Comments: 10471
Quoting mrpuertorico:
guess i have some prepairing to do


nice pic lol

saludos de ponce..
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Quoting Weather456:
Tropical depression 3 for sure



So 456 what are pr's chances for a double hit
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830
WHXX04 KWBC 151118
CHGQLM
ATTENTION...NATIONAL HURRICANE CENTER

NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR

TROPICAL DEPRESSION INVEST 90L

INITIAL TIME 6Z AUG 15

DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT
REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD
NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC
OFFICIAL FORECAST.


FORECAST STORM POSITION

HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)

0 12.4 32.0 270./17.1
6 12.2 33.8 263./17.6
12 12.1 35.5 265./16.3
18 11.7 36.8 254./13.4
24 11.5 38.4 263./15.4
30 11.5 40.1 271./16.8
36 11.4 41.7 265./15.5
42 11.7 42.9 284./12.7
48 11.9 44.3 277./13.8
54 12.3 45.8 285./15.5
60 12.8 47.4 287./15.9
66 13.1 48.9 284./15.0
72 13.5 50.3 285./14.3
78 14.1 51.8 292./15.8
84 14.6 53.5 286./16.9
90 15.0 55.2 283./16.5
96 15.4 56.7 283./15.5
102 15.8 58.2 288./15.0
108 16.7 59.5 302./15.2
114 17.3 61.1 291./16.1
120 17.7 62.7 285./16.1
126 18.4 64.0 300./13.9
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Quoting nrtiwlnvragn:
06Z HWRF Ana
How many hours out is that nrt?
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06Z HWRF Ana
Member Since: September 23, 2005 Posts: 13 Comments: 10471
4275. cg2916
We have Ana! And if NOAA listens to the QUIKSCAT that Weather456 posted, then we have TD3, too.
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Tropical depression 3 for sure

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Key West, Base Reflectivity 0.50 Degree Elevation Range 248 NMI

Something to watch?
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Quoting StonedCrab:


YIKES!
Glad I don't trust anything that is further out than 3 days.


lol a stoned crab

hey people i saw DISTRICT9 yesterday, recommended for all you sci-fi and action fans... peter jackson redeemed himself after king kong, it seems (sigh)
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4271. WxLogic
NOGAPS did pretty well this go around as it was able to successfully predict ANA development and to some extent ECMWF.
Member Since: August 14, 2008 Posts: 4 Comments: 4881
guess i have some prepairing to do
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Quoting StormW:


Because the forecast steering flow has changed slightly.

THE INITIAL MOTION ESTIMATE IS 270/14. THE GLOBAL MODELS ARE IN
AGREEMENT THAT A DEEP-LAYER RIDGE WILL STRENGTHEN NORTH OF THE
TROPICAL CYCLONE OVER THE NEXT DAY OR SO. THIS PATTERN FAVORS THE
TRACK OF ANA GRADUALLY BENDING FROM A WEST TO A WEST-NORTHWEST
DIRECTION WITH AN INCREASE IN FORWARD SPEED. THE ONLY SIGNIFICANT
OUTLIERS TO THIS TRACK ARE THE GFDL AND GFS...WHICH BOTH WEAKEN THE
SYSTEM RATHER QUICKLY...LEADING TO A MORE WESTWARD TRACK OF THE
CYCLONE. IN A FEW DAYS...SOME OF THE MODELS...SUCH AS THE GFS...
SHOW A WEAKNESS IN THE RIDGE OVER THE WESTERN ATLANTIC THAT COULD
ALLOW THE CYCLONE TO GAIN A LITTLE MORE LATITUDE. THIS WEAKNESS
APPEARS TO BE CAUSED BY THE MID- TO UPPER-LEVEL LOW CURRENTLY NEAR
25N 65W. HOWEVER...THE MAJORITY OF THE GUIDANCE SHOWS THE MID- TO
UPPER-LEVEL LOW MOVING WEST-SOUTHWESTWARD WITH MINIMAL INFLUENCE ON
THE STRENGTH OF THE RIDGE. GENERALLY...THE MODELS THAT HOLD ONTO
ANA ARE IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD. THE NHC
TRACK FORECAST IS SHIFTED TOWARD THE SOUTHWEST FOR THIS ADVISORY...
BUT NOT AS FAR AS THE MODEL CONSENSUS.


I'll be on later today with an update.
Waiting patiently for that update.
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Quoting java162:


its can anyone


Yes. I know didn't mean to offend you.
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Quoting stormpetrol:

Nice quikscat of 90l , looks like "Bill" might be soon here


I see that COC slightly under 12N... doesnt it?

11.6N... 32W something like that
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Quoting IKE:
Look where the 6Z NOGAPS takes Ana...and strengthens it significantly....shutter up those windows WS!


YIKES!
Glad I don't trust anything that is further out than 3 days.
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Quoting java162:


its can anyone


My guess for the northward shift of 90L is the strengthening of TD2 to Ana, and predicted further strengthening.

The proximity of the storms will cause them to interact via the Fujuwhara effect
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Link

Wave behind 90L lookin healthy. It's been developed by some models I reckon
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poor haiti there gonna get whuped again this year, oh sorry! did imention i disagree that they are going north of the leewards, well i firmly believe that these storms are gonna enter the caribbean and the cut north over haiti and or puerto rico. JMO
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Nice quikscat of 90l , looks like "Bill" might be soon here
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Quoting weatherwiz:
Yeah the Gulf is really warm and in actuality the SST values are higher in the GOM now then they were in 2005 when we had Katrina blow up. I just hope nothing trys to get into the GOM because if there is low shear and the environment is right it wouldn't look pretty.


actually, maybe it would, just nasty results
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4259. java162
Quoting homelesswanderer:


I'm sorry I can't answer your question but I had to do a double take I thought you had said xanax anyone? Lol. Sorry wishful thinking on my part. ;)


its can anyone
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4258. IKE
Accuweather take...
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Latest update from Crown WX Link
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It's going to be a looonnng couple a weeks.
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4255. WxLogic
Morning... I go on a little road trip and now we have ANA.
Member Since: August 14, 2008 Posts: 4 Comments: 4881
Quoting jasoniscoolman10:
look at tthis big wave on africa wow..


yeah, the GFS develops that Twave
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BOLETIN
DEPRESION TROPICAL DOS ADVERTENCIA NUMERO 12
NWS TPC/CENTRO NACIONAL DE HURACANES MIAMI FL AL022009
500 AM AST SABADO 15 DE AGOSTO DE 2009

...ANA SE FORMA EN EL OCEANO ATLANTICO TROPICAL...

INTERESES EN LAS ISLAS DE SOTAVENTO DEBEN MONITOREAR EL PROGRESO DE
LA TORMENTA TROPICAL ANA. UNA VIGILACIA DE TORMENTA TROPICAL SE
REQUIERE PARA PARTES DE LAS ISLAS DE SOTAVENTO TARDE HOY.

PARA INFORMACION ESPECIFICA EN SU AREA EN LOS ESTADOS
UNIDOS...INCLUYENDO LA POSIBILIDAD DE VIGILANCIAS Y AVISOS...POR
FAVOR MONITOREAR LOS BOLETINES EMITIDOS POR SU OFICINA LOCAL DEL
SERVICIO FUERA DE LOS ESTADOS UNIDOS...FAVOR MONITOREAR LOS
BOLETINES EMITIDOS POR SU OFICINA DE SERVICIO METEOROLOGICO.

A LAS 5:00 AM AST...09:00 UTC...EL CENTRO DE LA TORMENTA TROPICAL
ANA ESTABA LOCALIZADO EN LA LATITUD 14.6 NORTE...LONGITUD 46.8 OESTE
O COMO A 1010 MILLAS...1630 KILOMETROS...AL ESTE DE LAS ISLAS DE
SOTAVENTO.

ANA SE MUEVE HACIA EL OESTE A CERCA DE 16 MPH...26
KILOMETROS POR HORA...Y SE ESPERA ESTE MOVIMIENTO GENERAL CON UN
GIRO GRADUAL HACIA EL OESTE-NOROESTE DURANTE LOS PROXIMAS DIAS.

LOS VIENTOS MAXIMOS SOSTENIDOS ESTAN CERCA DE 40 MPH...65 KILOMETROS
POR HORA...CON RAFAGAS MAS FUERTES. SE PRONOSTICA FORTALECIMIENTO
LENTAMENTE DURANTE LAS PROXIMAS 48 HORAS.

LOS VIENTOS CON FUERZA DE TORMENTA TROPICAL SE EXTIENDEN HASTA 70
MILLAS...110 KILOMETROS FUERA DEL CENTRO.

LA PRESION CENTRAL MINIMA ESTIMADA BASADA EN LA BOYA DE NOAA 41041
ES 1005 MB...29.68 PULGADAS.

...RESUMEN DE LA INFORMACION EMITIDA A LAS 5:00 AM
AST...POSICION...14.6 NORTE 46.8 OESTE
VIENTOS MAXIMOS SOSTENIDOS...40 MPH
MOVIMIENTO ACTUAL...OESTE O 270 GRADOS A 16 MPH
PRESION MINIMA CENTRAL...1005 MILIBARES

LA PROXIMA ADVERTENCIA SERA EMITIDA POR EL CENTRO NACIONAL DE
HURACANES A LAS 11:00 AM AST.


$$

PRONOSTICADOR BLAKE


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Yeah the Gulf is really warm and in actuality the SST values are higher in the GOM now then they were in 2005 when we had Katrina blow up. I just hope nothing trys to get into the GOM because if there is low shear and the environment is right it wouldn't look pretty.
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4250. java162
can anyone explain why all the tracks have shifted northward????
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morning everyone looks like we are going to have a very long day, weather456 looks like you are first up with tropical storm ana
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Morning Folks!
I'm watching closely.
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4247. IKE
Quoting sporteguy03:


you might want to go back to sleep you might not rest for a week.


LOL.

Dr. Lyons thinks it's going to slowly strengthen and head for the Bahamas and south Florida/WS.
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Quoting WeatherStudent:
Good morning, all.
Good morning to you too.
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90l looking mighty impressive this AM
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Appears to be some turning on NWS Key West Long Range radar. This is just my untrained eye; don't jump to conclusions.

National Weather Service Enhanced Radar Image Loop
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Good morning everyone,

Well well well, I wake up and hear on the 6am news that we have TS Ana... like I am sure many of you have said already.. don't count a good swirl out..if it is still twirling it can still gather in some weather.

and how is 90L doing?

Just got at my work desk so got to go catch up.
Very wet down here in SE Florida this morning... no measureable rain at my house, just sprinkles but good rain out here in Weston.

bbl!



Happy Saturday everyone.
Gams
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Quoting WeatherStudent:
Good morning, all.


you might want to go back to sleep you might not rest for a week.
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Rhut rho...he's awake! sshh...don't tell him

BB -I NEED coffee
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4239. IKE
Good Saturday morning to all.....

Good coffee....Maxwell House caffeine light.....
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Morning all: The storms were busy getting their acts together overnight, I see. Time to go check the genny. Weather 456 - great update in your blog.
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mmmmmmmmmm! morning all, just reading and checking all data also watching how much the atl high and that ull east of florida will affect tracks!!
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Ike, May be in our best interest to lock the door on Pat. Yesterday, every post he had was bad for you and me...LOL
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90L is rather classic looking
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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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