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 TexasWynd:
If its true? Take it as a honor badge. Wear it proud lol.

LMAO!
Member Since: August 2, 2006 Posts: 0 Comments: 1240
The GFS is still screwed up......LOL
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SERVICIO NACIONAL DE METEOROLOGIA SAN JUAN PR
546 AM AST SABADO 15 DE AGOSTO DE 2009

LA DEPRESION TROPICAL DOS...FUE DECLARADA POR EL CENTRO NACIONAL DEHURACANES LA TORMENTA TROPICAL ANA A LAS 5 AM DE ESTA MANANA.EN ESTOS MOMENTOS SE PRONOSTICA QUE SU TRAYECTORIA PASARA A UNAS 50MILLAS DE LA COSTA NORESTE DE PUERTO RICO EL LUNES EN LA TARDE CONVIENTOS DE TORMENTA TROPICAL. ES POSIBLE QUE OTROS SISTEMAS TROPICALES...QUE TODAVIA NO SE HAN DESARROLLADO...TAMBIEN SE ESPERA QUE AFECTEN EL AREA LOCAL EL JUEVES Y EL SABADO. EL SERVICIO NACIONAL DE METEOROLOGIA DE SAN JUAN EMITIRA MAS BOLETINES ACERCA DE ESTOS SISTEMAS CUANDO SE TENGA UNA INFORMACION MAS PRECISA ACERCA DE LA INTENSIDAD Y TRAYECTORIA DE ESTOS SISTEMAS. LOS RESIDENTES YVISITANTES DEBEN COMPLETAR SU PREPARATIVOS PARA ENFRENTAR LAS
INCLEMENCIAS DEL TIEMPO. PARA MAS INFORMACION POR FAVOR CONSULTAR NUESTRA PAGINA EN LA INTERNET Y ESTAR PENDIENTES A LOS BOLETINES PUBLICOS QUE SE EMITIRAN ESTA TARDE.
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Quoting WPBHurricane05:


LOL???
If its true? Take it as a honor badge. Wear it proud lol.
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Quoting IKE:


Just spit coffee on keyboard...

Shear?

Where?

It's under 5 knots....of shear....okay, 5.2 knots...



Dont be tellen me...tell mr. hurricanelover.
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4479. jipmg
Bill is looking way better than ana, even the spin seems to be stronger (stronger winds being recorded in the quick scat than in ana), ana on the other hand will be fighting dry air the entire day.
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4478. IKE
Quoting WPBHurricane05:


wow! Thanks!

:rolleyes:


Just spit coffee on keyboard...

Shear?

Where?

It's under 5 knots....of shear....okay, 5.2 knots...

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Quoting Weather456:


lol I went to bed around 1am but woke up when the 5am was already posted. Trust me, I cant see myself staying up for advisories, maybe with Wilma rapid intensification that morning. I always tell my self the 5am update will be there in the morning.


Ya this is true. lol. I couldnt stay up anyway if I tried. I love my sleep.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
Sweet...I said Ana would hit somewhere between the Cape and south Fl over a week ago. So far that is what it looks like she is going to do. Now I am glad i was right on that but man I hope I am wrong on 90L. Still think either Homestead area or it sneaks into the Gulf.
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4475. JRRP
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Quoting WeatherStudent:


Ignored.


LOL???
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Quoting hurricanelover236:
I can assure you that florida is safe from Ana. It is so weak its going to stay west and in my opinion be a gulf storm. It will also stay weak if it survuves because it has a alot of shear and dry air to battle. florida u can breath easy because ana is not coming. Im telling you.

Golly! Gee Whiz! I'm SO relieved! YOU have spoken! And who are you again?
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Quoting WPBHurricane05:


wow! Thanks!

:rolleyes:


lol
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Sat. Images seem to suggest 90L has developed a closed circulation. With the little wave coming in the gulf today and Ana and Bill coming, looks like the NHC boys are gonna get busy at last.
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Quoting Weather456:
90L has a dvorak of 2.5

a well define circulation with atleast 30 knot winds

very organize convection

TD 3 at 11am



or a TS
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Quoting alaina1085:


Wow I wish I could have stayed up all night for it.


lol I went to bed around 1am but woke up when the 5am was already posted. Trust me, I cant see myself staying up for advisories, maybe with Wilma rapid intensification that morning. I always tell my self the 5am update will be there in the morning.
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oh lord the wishcasters are out in full effect. So may are pointing the storms to their neck of the woods...... imo just stick to what you know and leave the forecasting to the professionals or non wishcasters
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4465. IKE
Ah-nah looks to be moving just north of west.

Bill is about to be born. Huge system....give it about 2-3 days and he's headed for a cane.
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Quoting hurricanelover236:
I can assure you that florida is safe from Ana. It is so weak its going to stay west and in my opinion be a gulf storm. It will also stay weak if it survuves because it has a alot of shear and dry air to battle. florida u can breath easy because ana is not coming. Im telling you.


wow! Thanks!

:rolleyes:
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Quoting Weather456:


they re classified it TD2 then at 5am we had Ana. It was the most NHC dilemmas I ever saw.


Wow I wish I could have stayed up all night for it.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
90L has a dvorak of 2.5

a well define circulation with atleast 30 knot winds

very organize convection

TD 3 at 11am
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I can assure you that florida is safe from Ana. It is so weak its going to stay west and in my opinion be a gulf storm. It will also stay weak if it survuves because it has a alot of shear and dry air to battle. florida u can breath easy because ana is not coming. Im telling you.
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Dvorak indicates 90L has skipped over TD status and its Bill. 2.5 from both agency.
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Quoting Seflhurricane:
best advise to all is to have your preparedness plan ready
Agreed. It's time to review your hual and/or hunker plans. A few bloggers on here have good blogs regarding what should be part of your plan. Ready.gov is a good place to start.
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Ana has the benefit of venting from the ULL to her NW, but she is still surrounded by dry air. 90L looks like it may be re-categorized as a named storm, Bill, and just skip the TD category.
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4457. IKE
Quoting alaina1085:

Haha, so I see. Was this the advisory they classified Ana as a TS?


Updated to TS at 4 am CDST.
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Quoting BenBIogger:
I think Ana will stay south of Florida.
i hope
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Quoting alaina1085:

Haha, so I see. Was this the advisory they classified Ana as a TS?


they re classified it TD2 then at 5am we had Ana. It was the most interesting NHC dilemmas I ever saw.
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Ok out for now my daughter has Soccer Practice at 9:30. BBL
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hmmm i wounder if we will hit 5,000 commets be for dr m update is blog later
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I think Ana will stay south of Florida.
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4450. JRRP
Quoting ackee:
90L continue a slight WSW movement wonder if this will change the GFS and other models next runs ?

this WSW motion was forecast by the models
Link
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Quoting Weather456:


yea 12:30 am, the NHC likes messing with us.

Haha, so I see. Was this the advisory they classified Ana as a TS?
Member Since: August 2, 2006 Posts: 0 Comments: 1240
DATE/TIME LAT LON CLASSIFICATION STORM
15/1145 UTC 11.4N 33.5W T2.5/2.5 90L
15/1145 UTC 14.3N 47.2W T2.0/2.5 ANA

Ana has trouble with dry air.

And according to Dvorak, Bill is born.
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Quoting HurricaneKyle:


Dean is the closest one out there, the similarities are stunning.


and Georges....
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Quoting ackee:
90L continue a slight WSW movement wonder if this will change the GFS and other models next runs ?
check the GFDL MODEL!!!
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OK guys - just woke up to thunder and Ana. I see Ana is heading my direction (SFL) - what about Bill - some of the models are curving him north just as he approaches the east coast of FL.. Is there a possibility of Bill following Ana with a SFL landall? I can't get my head around the models right now.
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though early I hate to spoil the party for kman but it looks like Ana will be and e coast storm (most likely FL) and I'm hoping that 90L (Bill) will be nothing but a fish storm.
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4443. IKE
Ah-nah has a nice circulatory appearance on satellite...see very little shear...

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StormW. I wanted to thank you for all your expert knowledge not only on here but in your email updates. I forward them to my manager, who also is the company Hurricane person. Also sent your email update and this blog to my accountant friend in St. Pete.
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Quoting alaina1085:


Did that advisory ever come in? lol... I fell asleep waiting.


yea 12:30 am, the NHC likes messing with us.
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Quoting drg0dOwnCountry:

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


Dean is the closest one out there, the similarities are stunning.
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Bill or any of you knowlegable folks, How close to eachother do the storms have to be for a Fujiwhara Effect to occur. Could the western side of 90L pull Ana South...Long time lurker and learn a lot from you all. But that question just came tom mind as it appeared from the satellite view that Ana was starting to have a WSW motion.
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best advise to all is to have your preparedness plan ready
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Quoting ackee:
90L continue a slight WSW movement wonder if this will change the GFS and other models next runs ?


i dont how much they will change at 12Z but as I stated in my blog, 90L is following Ana, which is following the tropical wave near Florida.

They are all following one line
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HWRF 6Z
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4435. JRRP
Quoting Weather456:
another F5 session later this morning. The little that are still fucntion after last night late advisory.

LOL
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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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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.