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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SATELLITE IMAGES INDICATE THAT THE AREA OF LOW PRESSURE CENTERED
ABOUT 475 MILES WEST-SOUTHWEST OF THE WESTERNMOST CAPE VERDE
ISLANDS CONTINUES TO BECOME BETTER ORGANIZED...AND A TROPICAL
DEPRESSION MAY BE FORMING. IF CURRENT TRENDS CONTINUE...ADVISORIES
WILL LIKELY BE INITIATED LATER TODAY
. THE LOW IS EXPECTED TO MOVE
WESTWARD AT ABOUT 15 MPH. THERE IS A HIGH CHANCE...GREATER THAN 50
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.
Member Since: Posts: Comments:
3733. KEEPEROFTHEGATE (Mod)
thanks tidewater
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3731. Drakoen
NOGAPS 00z takes 02L into south Florida
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I just hope everything misses Cuba this year.. Planning on going there for our 30th anniversary.. two weeks around December/January
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3729. Skyepony (Mod)
Quoting Patrap:


Roger that ,..thankie much.

Will be busy time a coming seems for the crews and Maintenance folk.


Kinda think we may have been treated to these research missions because things have been so slow. Pretty rare to see them go this far east.
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3728. Drakoen
It also appears to me that 90L is much better organized.
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Quoting truecajun:
so the weather channel said, not one, not two, not three, but FOUR areas of interest. what say you about the carib area and florida areas. florida wave will just bring rain right?


Just a rainmaker for now, but the 200 mb flow is forecast to be favorable for tropical cyclogenesis (development), and the tropical wave over Cuba may interact with the trough in the NE GoM in two days or so, potentially generating an area of convection.
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Quoting RainyEyes:
Will there be a 2am update? Just wondering is I want to stay up :-)
It was wild in here at 11 becouse that update was wayyyy late!!
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3724. Skyepony (Mod)
Around 2am we get a NHC discussion, most the 00Z models are done by then. Also a new position & T#.
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3723. Patrap
Quoting Skyepony:
Pat~ They may have had time to get some of the earlier recon in the models but not all of it. I'd look the 6Z run over good.


Roger that ,..thankie much.

Will be busy time a coming seems for the crews and Maintenance folk.
Member Since: July 3, 2005 Posts: 424 Comments: 128259
3722. peejodo
Something's fishy?????????
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3721. Drakoen
I didn't expect to see 02L come back so soon lol. I see the GFS has shifted dramatically to the north with the new data fro the NOAA plane
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Will there be a 2am update? Just wondering is I want to stay up :-)
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3719. Skyepony (Mod)
Truecajan~ Been here all along. That wave over Cuba, a low has been trying to get going on it & on cuba today. If that gets N of Cuba may suprise many. CMC been spinning up a small storm that hits the keys, Tampa & into the panhandle. Shear & land is all that is hampering it.
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just as i login, i realize how tired i am. gotta hit the sack.
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Quoting KEEPEROFTHEGATE:
TideWaterWeather i myself use info coming out of norfolfk on a regular basis that and the NHC of coarse and my own obsevations put it all together and you get a reasonable forecast


Keeper.. I have been watching your posts a long time.. i like them... i know a fair amount about hurricanes... its just that there are so many voices here and often bad feelings and nasty comments.. i choose to remain silent...
Truth is.. many of the experts here just mine the internet for info.. and then post it as their own.. most times i can catch the copy and paste quickly...... most times from JB or the like.....I scan prob 100 sites for info and sat data... i see many copy and paste actions by the board "experts"..anyway.. your posts are always legit...hoping nothing rolls through Key west,,, all it takes here is a tropical storm to cause big problems
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Quoting druseljic:


Wow. That's awesome!


Yeah, that is pretty awesome. Almost makes the world seem like such a small place when you think about moisture/systems going from continent to continent!
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3714. Skyepony (Mod)
Pat~ They may have had time to get some of the earlier recon in the models but not all of it. I'd look the 6Z run over good.
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Quoting atmoaggie:

TX A&M 2003. I somehow did fairly well in dynamics...but I do hear you about that lost Whiskey Tango Foxtrot feeling. It cropped up at once per lecture.

I remember most having the derive the RTE WITH clouds...on an exam Fun.


We never had to do it on an exam... or I'd still be in school. We did it on a few assignments, it's a killer.

A&M's a great school, I had a friend who transferred there.

I stayed in Monroe, fell into a job at the NBC/FOX affiliates here.

I'm really outta here now, it's been one heck of a week.
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hey skypony. haven't seen you since last year.
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3711. Patrap
Quoting Skyepony:
Wunder how much recon made it in the 00Z run.


Skyepony..hear any words if the run caught a smattering of G-4 input..?
Member Since: July 3, 2005 Posts: 424 Comments: 128259
so the weather channel said, not one, not two, not three, but FOUR areas of interest. what say you about the carib area and florida areas. florida wave will just bring rain right?
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Quoting sammywammybamy:



Join us in Tropics Chat? Please?


What is the trick to joining the chat? I signed in with user name and password, and have the latest version of the Flash player, but only get a "connecting to server" message that hangs. If you have a minute, would you let me know, please? Thanks.
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3708. GatorWX
Quoting ackee:
TD#2 seem like it is taken a slight WSW movement anyone else see that ?


No, but it does seem shear is lessening over it allowing convection to fire up to its south and bands to form to its north. Looks to be strengthening
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Quoting wxmanjarod:


Yeah, I was probably the guy in the back with every equation typed in code into my TI-83 calculator!

University of LA-Monroe grad, 2006.

I think I got lost after the Geopotential Height equation... stayed confused for 2 years. Then, everything clicked, and the Vorticity Equation actually made sense. That was the happiest and scariest day of my life.

TX A&M 2003. I somehow did fairly well in dynamics...but I do hear you about that lost Whiskey Tango Foxtrot feeling. It cropped up at once per lecture.

I insisted on using my TI-86 so I could convert units with a couple of strokes. Torr to hPa got annoying.

I remember most having the derive the RTE WITH clouds...on an exam. Fun.
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3706. Patrap
Technical Attachment

AN OVERVIEW OF NHC PREDICTION MODELS

Bernard N. Meisner
Scientific Services Division
National Weather Service Southern Region


Introduction

Meteorologists at the National Hurricane Center (NHC) have a variety of prediction models available to provide guidance for their forecasts of tropical cyclone tracks and intensity. The intent of this paper is to provide a brief overview of each of the models. Forecasters may find this information helpful when considering NHC discussions which mention the performance of individual models. A primary reference is provided after the summary of each model for readers who desire more information. NOTE: All thumbnail graphics in this Web document are linked to larger version of the graphics. Just click the thumbnail to view the larger version.

As noted by Neumann (1979), models for the prediction of tropical cyclone motion and intensity may be classified as either statistical or dynamical. Statistical models rely on what has happened-the climatology of past storms, for example. Dynamical models can be classified as either barotropic or baroclinic. Statistical-dynamical models are an intermediate class that incorporate numerically forecast data into a statistical prediction framework, similar to the Model Output Statistics used to provide guidance for specific parameters such as temperature and probability of precipitation.
Member Since: July 3, 2005 Posts: 424 Comments: 128259
Quoting southfla:
Has anyone seen the PSU NHEM (northern hemisphere) satellite animation ? Very cool watching the tropics moving east to west and the northern jet stream troughs moving west to east.



Wow. That's awesome!
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Quoting druseljic:


Thanks, no matter how much I read about the MJO, it still perplexes me :-)

Don't worry. So far it still perplexes our current operational global models, too.

Did get a spike...short lived?
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3703. KEEPEROFTHEGATE (Mod)
TideWaterWeather i myself use info coming out of norfolfk on a regular basis that and the NHC of coarse and my own obsevations put it all together and you get a reasonable forecast
Member Since: Posts: Comments:
Quoting atmoaggie:

Whoa, you were in my dynamics classes? Sounds like em!


Yeah, I was probably the guy in the back with every equation typed in code into my TI-83 calculator!

University of LA-Monroe grad, 2006.

I think I got lost after the Geopotential Height equation... stayed confused for 2 years. Then, everything clicked, and the Vorticity Equation actually made sense. That was the happiest and scariest day of my life.
Member Since: Posts: Comments:
An observation,,, I dont feel the need to post much, but i am a long time lurker... I am in the Navy for my 21st year, i was prior stationed in Norfolk, Va.. thus the name Tidewater weather..
Anyway... i am now in Key west.. I have always loved hurricanes... now that i am on an island that is just about at sea level... i have much more concern than before. i have been commenting to people that it only takes one or two hurricanes to put a season in the record books... it has been quiet up till now.... and now we have potential development in several places. while i watch in anticipation, i have a new found respect for mother nature..... i cant help but think back to those poor folks in texas that got hit with a storm surge much larger than expected.. I appreciate all the informational post, even the wish/down caster ones..

Ron

AB'S OR WANABEES
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Quoting WeatherStudent:
Yes, it has to do with the recent upward spike in the MJO over our basin. :)


Thanks, no matter how much I read about the MJO, it still perplexes me :-)
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Quoting atmoaggie:

Whoa, you were in my dynamics classes? Sounds like em!

If j is an imaginary number?
How come j * (-j) = -1
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Has anyone seen the PSU NHEM (northern hemisphere) satellite animation ? Very cool watching the tropics moving east to west and the northern jet stream troughs moving west to east.

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Both lows appear to be holding their own.
Link
Goodnight.
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Quoting KEEPEROFTHEGATE:
i am not a forecaster tim never have never been just a hobby my idea of a stamp and coin collection

lol

and i call it as i see it 02l died and was reborned just as was stated just the facts friend


Good god.. don't use facts, that just confuses him.
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Quoting wxmanjarod:


Yeah, I'm still reading... and I do remember all that.

Do you realize what you're doing to me? Bringing back flashbacks of Dynamics classes, where I walked out naseous every Monday, Wednesday, and Friday. I thought I had drank most of those memories away.


Whoa, you were in my dynamics classes? Sounds like em!
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3692. KEEPEROFTHEGATE (Mod)
Quoting TampaSpin:


Thats one of your better forecast jobs.......LMAO
i am not a forecaster tim never have never been just a hobby my idea of a stamp and coin collection

lol

and i call it as i see it 02l died and was reborned just as was stated just the facts friend
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Quoting robie1conobie:
funny, I am no expert, but I think they fire up more when they lose the suns heat. I think that is what everyone has been referring to as dmax. correct me if I am wrong.


No, that is quite correct. Convective activity increases at nighttime over the ocean.
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1-2 punch for florida...Lets hope not.

Have a great night.
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Quoting atmoaggie:

You probably will not read this, but do you remember that most all of our physics proofs start out with "assume the sin of theta equals theta"? Only actually happens when theta is zero...almost never for most of those physics principles.


Yeah, I'm still reading... and I do remember all that.

Do you realize what you're doing to me? Bringing back flashbacks of Dynamics classes, where I walked out naseous every Monday, Wednesday, and Friday. I thought I had drank most of those memories away.

You're right though... too many assumptions that cause a ripple effect of imperfections. Like we said... "Garbage In, Garbage Out".

Geez, I'm glad someone can relate to this. Thanks for re-instilling my faith in this comment section.
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3688. ackee
TD#2 seem like it is taken a slight WSW movement anyone else see that ?
Member Since: July 15, 2008 Posts: 0 Comments: 1372
What are they calling this now?
Link
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i heard some of why its been queit was wind shear and sarah dust over the area
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About

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