TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 2:38 PM GMT on August 13, 2009

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Tropical Depression Two is near death, but is still worth watching. The dry, Saharan air to the north and west of the depression, combined with moderately high levels of wind shear of 15 - 20 knots, have almost completely destroyed all of TD 2's heavy thunderstorms. Satellite loops of the storm show a well-formed circulation, but almost no heavy thunderstorm activity.

Wind shear over TD 2 is expected to remain in the modereate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C three days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to to TD 2's north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that TD 2 will not be able to intensify quickly, and some of the models indicate the TD 2 may get destroyed in the next day or two. However, several models still predict TD 2 will become a tropical storm. The HWRF model predicts TD 2 will become a hurricane five days from now, but this seems unlikely given the dry air and relatively high wind shear affecting the storm.


Figure 1. Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

African tropical wave 90L
A strong tropical wave with a large circulation and plenty of heavy thunderstorm activity is a few hundred miles south of the Cape Verdes Islands, off the coast of Africa. NHC dubbed this disturbance 90L this morning. This morning's QuikSCAT pass shows that 90L has a very large circulation, and top winds of about 30 mph. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are in two major bands, to the north and to the south of the center. There is no heavy thunderstorm activity near the center yet, and this would have to happen before 90L can be named Tropical Depression Three. 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 has been. Wind shear is about 20 knots over 90L, and is forecast to remain in the moderate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days, which are high enough above the 26°C threshold for tropical cyclone formation to allow some slow development to occur. The GFS and ECMWF models continue to predict the development of this wave, though they are now less aggressive about intensifying it than they were in earlier runs. The consensus among the reliable HWRF, GFDL, GFS, and ECMWF models is to bring 90L to point near or just north of the northernmost Lesser Antilles Islands 6 - 8 days from now. The storm could be at hurricane strength by then, as forecast by the SHIPS intensity model.

I'll have an update Friday morning.

Jeff Masters

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Quoting tiggeriffic:
Hello all...hard to believe it's been almost a year since we were all here doing this last year...except last year we started WAY before this...el nino, la nina...let's see what happens in the next couple days...


hey neighbor
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Is there an 11:00 update tonight?
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2535. tkeith
I think (without any facts to back it up,mind you) the wave over Hispanola is gonna get me wet here in NOLA.
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Greta Van Sustren is a disappointment.
She is an intelligent looking woman, albeit a weird-looking one, that looks like she will say something and then says nothing at all.
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Quoting tiggeriffic:
Hello all...hard to believe it's been almost a year since we were all here doing this last year...except last year we started WAY before this...el nino, la nina...let's see what happens in the next couple days...


Hey tigggger long time no see
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Gotcha. I appreciate it.

I'm going to bed, goodnight everyone.


Oh wait almost forgot didn't you want to talk about schools
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Good evening

So, another ho hum evening waiting for the tropics to do something ?

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Hello all...hard to believe it's been almost a year since we were all here doing this last year...except last year we started WAY before this...el nino, la nina...let's see what happens in the next couple days...
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The Caribbean wave looks better. TD 2 looks done. 90L looks somewhat better. Where's Stephanie Abrams tonight??. She's the best...what a learned weather girl she is. Not since Kelly Bundy....
Member Since: July 10, 2007 Posts: 0 Comments: 418
Quoting weatherblog:


Yes, Wilma..
just opinions no, but actual situations of life or death during a storm...YES...
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Gotcha. I appreciate it.

I'm going to bed, goodnight everyone.
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2525. Patrap
NexSat 90L Loop
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Quoting TampaSpin:


This is one reason why.....it just genearlly does not do that when that far out....but, it can!



Secondly the Bermuda High is currently not forecast to push that far South and West currently......Hey it can change but, currently models are not showing that...Wait and see is what we have to do.
Thanks, TampaSpin
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Quoting SouthALWX:
umm .. isnt that showing negative convergence aka divergence ...or did you mean TD2

Hey, you are correct. Nevermind. Back to the "Caribbean wave is a big nuthin" mood. Pfffft pending.
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EUMETSAT Real Life Imagery
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting KATRINABILOXIGIRL:
have you ever been through a cane before especially a
really bad one?


Yes, Wilma..
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2520. Patrap
RAAMB
Currently Active Tropical Cyclones
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2519. ackee
Iam goimg wait and see with 9OL so far nothing has live up to expectation
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Quoting HurricaneJoe:


What does that mean? An increase in vorticity?

From a practical standpoint of giving an answer without calculus: Detectable spin in the clouds tracked by satellite analysis software or by wind analysis.

True definition here: http://www.theweatherprediction.com/habyhints/56/
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Quoting jpsb:
Speculation on where 90L is going as a Cat5 hurricane is, perhaps, a bit premature. So far this year we've seen EVERYTHING die before even making it to TS status. Maybe 90L will fare better maybe not. I live on Galveston Bay so am payng attention to the topics. My experience is tracking models are unreliable after three days and intensity models are unreliable period. As an experienced hurricane dodger I only worry at landfall -48 hours. 48 hours out tracking models start getting reliable, then I watch to see witch side of the storm I am going to be on. Dirty side, very bad, good side not so bad.


Nice try, but people here worship models. It's ok, i guess, in a way to have fun... gets people alert, at least. At worst, it instills misinformation and terror. Sometimes I wish the models weren't available to the public at all :D

But I totally get you! My overused phrase of the week on the blog: models tend to epic fail...

Meanwhile, I'm excited about the prospect of a surf-happy August-September for Puerto Rico :D
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Quoting RainyEyes:


Hey, I see you are from Marco Island...I am from Cape Coral. What news are you watching? I was watching nbc-2 last night and they said that Ana was named...I came onto WU all kinds of confused. I am hoping for some good rains too! My garden is dead!


I think it was WINK... we were just watching the 10pm.

Headed off for the night, night everyone
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If it gets in the gulf it needs to be watched.
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Quoting HaboobsRsweet:
My beef is when people shut down other folks that are suggesting where they think a storm may go and the only reason someone is shutting them down is the same excuse we hear all the time, it is too far out to say that. This is not an offical forecast so who cares if they say they think the storm is GOM bound or east coast bound. More power to them for trying. Not everyone has to explain in detail why they feel how they feel, it would help the rest out but it is not needed.
We should respect all of our divergent opinions, whatever they may be, and wait and see which one did or did not pan out.
Member Since: July 10, 2007 Posts: 0 Comments: 418
2513. tkeith
Quoting presslord:


I'm just here 'cause I can't stand to watch Greta van Susteren...
She does at least look a little better after those facelifts...
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Quoting AllBoardedUp:
My question is why do most people on here feel that 90L will hit the CONUS and not keep going straight across the Caribbean into the Yucatan, say around Belize or Cozumel? Is it because the models don't show this or is everyone seeing something else. Go easy on me, I don't have a clue! I'm on here to try and learn. (and be entertained of course)


This is one reason why.....it just genearlly does not do that when that far out....but, it can!



Secondly the Bermuda High is currently not forecast to push that far South and West currently......Hey it can change but, currently models are not showing that...Wait and see is what we have to do.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
2511. Patrap
Quoting atmoaggie:
I am doubtful...but just maybe.

Starting to have a little lower convergence:


Thats starting to concern me more tonight than 6 hours ago atmo
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Most Recent Microwave Imagery for Invest 90L

(Source: Navy/NRL Tropical Cyclone Page)

With this recent microwave pass, it suggests that Invest 90L continues to gradually become better organized with obvious spiral banding pattern established and well defined low-level circulation center. In this microwave pass, you can also see the deep convection near the circulation trying to wrap around the center further indicating improving organization. Going to be really interested to see a new QuikSCAT pass for further support and to see the wind speeds occurring with that deep convection on the western flank of the circulation center. Still has some work, but its getting closer to becoming a tropical cyclone.
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Quoting presslord:


I'm just here 'cause I can't stand to watch Greta van Susteren...


Hear, hear.
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umm .. isnt that showing negative convergence aka divergence ...or did you mean TD2
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2507. Patrap
Quoting Comradez:
TD2 is firing up again...the environment is moistening to the north, and some spiral bands are firing up again, meanwhile as just enough convection stays aflame over the COC. According to the CIMSS shear maps, shear should actually be weakening as TD2 heads further west. I think TD2 might become Ana before 90L gets a chance to get organized.

If TD2 gets stronger than the models are predicting, will that create a weakness in the high that 90L will follow further to the north?



Id try some new er,Contacs or Frames cuz TD 2 done went Das Poof.

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Quoting weatherblog:
As much as I would love to someone's life, my opinion shouldn't merit such a life or death decision.
have you ever been through a cane before especially a
really bad one?
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2505. AndyN
I've been reading with interest the discussion about the GOM. What if anything is supposed to kickstart this depression? Also, I read an earlier post referencing the 90L and TD2. I agree, it could get interesting next week.
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I am doubtful...but just maybe.

Starting to have a little lower convergence:
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As much as I would love to someone's life, my opinion shouldn't merit such a life or death decision.
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Quoting atmoaggie:

And if you look further back, you will see the diurnal cycle. that wave had an increase in vorticity 24 hours ago, too...then decreased. Will be repeating.


What does that mean? An increase in vorticity?
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TD2

90L

AOI

Member Since: October 1, 2007 Posts: 81 Comments: 26511
TD2 is firing up again...the environment is moistening to the north, and some spiral bands are firing up again, meanwhile as just enough convection stays aflame over the COC. According to the CIMSS shear maps, shear should actually be weakening as TD2 heads further west. I think TD2 might become Ana before 90L gets a chance to get organized.

If TD2 gets stronger than the models are predicting, will that create a weakness in the high that 90L will follow further to the north?
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Quoting wunderkidcayman:

I think it has a chance of develop before it reaches the caribbean and looking at the 850 mb vorticity in the last 6hours till now if you look at it close you can see that the vorticity has increased





And if you look further back, you will see the diurnal cycle. that wave had an increase in vorticity 24 hours ago, too...then decreased. Will be repeating.
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sorry, keyboard went out. Whats I.K.E?
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Quoting MarcoIsland:
hey all.

i remember someone on here mentioned not too long ago that they were looking to start a hurricane/tropical weather related site. I forgot who that was and I had meant to send them a message and let them know I have a few good domains that I have been waiting to do something with but haven't gotten around to yet. If you're still out there shoot me a WU-Mail when you get a chance. Thanks!


Local weather here has been playing up 90L and the wave over Puerto Rico tonight. Hopefully the wave won't develop and we'll get some nice rains here this weekend.


Hey, I see you are from Marco Island...I am from Cape Coral. What news are you watching? I was watching nbc-2 last night and they said that Ana was named...I came onto WU all kinds of confused. I am hoping for some good rains too! My garden is dead!
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2496. Patrap
With a LARGE CV Hurricane,Its takes a while for it to get to TS Status,and then to Canes Status due to the LARGE Size that it is. But when it gets the Ol Mo a rolling its a force that can sometimes plow thru synoptic challenges.

And even when they do fade,some..all that wave action and energy has to go somewhere,unfortunately its usually a Coastline.

Be ready,Have a Plan..Know what you are going to do NOW.
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My question is why do most people on here feel that 90L will hit the CONUS and not keep going straight across the Caribbean into the Yucatan, say around Belize or Cozumel? Is it because the models don't show this or is everyone seeing something else. Go easy on me, I don't have a clue! I'm on here to try and learn. (and be entertained of course)
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Quoting TampaSpin:
TD2 is actually tapping in to some moisture supplied by 90L it appears......hum this could get interesting in 2 days...


Long term swell forecasts for Puerto Rico bring 15 feet swells near by Wednesday, I imagine from the remnants of TD2.

Other interesting models develop an Apocalyptocane behind current 90L.

Speculate, shmeculate!
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Quoting hahaguy:


I'm not a doctor but I play one on tv.

Dude, you get into the character that is your avatar a little too well.
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Intergated kinetic energy
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Quoting KATRINABILOXIGIRL:
Not that I am being partial here but just to repeat as I said before He has saved many lives many times including mine and did so very much during Katrina before, during and after and we thank him for that with that I am off to bed will see what tomorrow brings
Good night. Tomorrow is another day and maybe more will be known about where TD2 and 90L will go.
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Just checked to see if any pressure was falling in the Bahamas mess and could not find anything showing anything falling. Gonna be a nice rainmaker for South Florida and MobilGirl your right this needs to be watched as it heads toward the GOM.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting weatherblog:


I am not here to save lives. That's not my job. Sure, it would be nice if I did, but I doubt my opinion will save someone's life.
Not that I am being partial here but just to repeat as I said before He has saved many lives many times including mine and did so very much during Katrina before, during and after and we thank him for that with that I am off to bed will see what tomorrow brings
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2487. jdjnola
Quoting TampaSpin:
TD2 is actually tapping in to some moisture supplied by 90L it appears......hum this could get interesting in 2 days...


I've noticed some of the models indicating a slight Fujiwhara effect between the two lows... thought it was interesting, but didn't think much of it beyond that.
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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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