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 tikikopamsxm:
hello everybody,
can you tell me how stong will be 90L around the northern islands


models greatly differ but average out a strong TS or minimal hurricane
Member Since: July 24, 2005 Posts: 407 Comments: 19076
3186. IKE
Quoting Weather456:


It does favor western-Pac looks.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
3185. IKE
Quoting stoormfury:
i notice all the downcasters have fled the blog
reality is here


The only thing left is...it's still just an invest. I agree, it is...but it won't last. This will be a named system.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
hello everybody,
can you tell me how stong will be 90L around the northern islands
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3183. cg2916
Good morning everybody!

Well, can't say I'm not surpsrised. I thought the Hispaniola wave would be back, but I can't believe that the remnants of TD 2 are code ORANGE! Didn't expect much else with 90L, thought it would stay red. The models are scaring me a little with 90L. Usually the CMC is about the only one that's in constant apocalyptic mode. This will be an interesting day.
Member Since: December 21, 2007 Posts: 13 Comments: 3032
Member Since: July 24, 2005 Posts: 407 Comments: 19076
i notice all the downcasters have fled the blog
reality is here
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3180. IKE
Quoting DaytonaBeachWatcher:
yeah a lot of similarities, but in my opionion, it wont make it that far west.


I'm trending toward saying it will, but, it's just a trend....

I think the northern islands are becoming a 50/50 on being hit.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting CybrTeddy:


That is not a Category 3 pressure though.. wow.


not the pressure, the intensity guidance already compensates for that error

The HWRF is the model at the very top of 120 hrs

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting IKE:
Gosh I hate to bring in a comparison because 90L is an invest still...and one has zero to do with the other, but...are these similar....

yeah a lot of similarities, but in my opionion, it wont make it that far west.
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3177. IKE
Gosh I hate to bring in a comparison because 90L is an invest still...and one has zero to do with the other, but...are these similar....date...letter of storm....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Very impresive

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Weather456:
HWRF brings 90L to a cat 3



That is not a Category 3 pressure though.. wow.
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Always welcome, archer. Hope it clicks for ya. Don't make it too complicated.
Ahh WORK.
That lovely four letter word. (I'm a second shifter so I just got off a little while ago.)

Have a good day.

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Quoting ALCoastGambler:
Good morning Ike and Weather 456. Another beautiful day in paradise is store for us today in "lower AL' Ike? lol
School has started again so I can't sucker any local kid into doing the yard work for me....lol


morning
Member Since: July 24, 2005 Posts: 407 Comments: 19076
3172. IKE
90L is the perfect example of...it only takes one.

It would be the A storm.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
HWRF brings 90L to a cat 3

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Good morning Ike and Weather 456. Another beautiful day in paradise is store for us today in "lower AL' Ike? lol
School has started again so I can't sucker any local kid into doing the yard work for me....lol
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3169. IKE
Looking at a 1015 visible on 90L...TD3 is getting close.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Thanks NolesFan for posting the "mirror image" of the Trop Cyclone. Helps some with my question, but since there is no indication of the interaction with the Upper Level AntiCyclone circulation, the image is half of what I need to envision. Good help anyhow, Thank you for looking for something to clarify for me. I will keep my tiny little mind working on this one, haha. Have to get ready for work, gotta go, but thanks for your efforts folks, I appreciate it. Have a great weekend, Storm Fans. And keep that 90L critter away from me in S FL...!!!
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3167. IKE
Just watching TWC. John Hope would turn over in his grave watching that garbage on there.

Shame on them.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


I've never understood what the 30 meant. I was going to ask on here, just never did???

What does that 30 mean?


lines of equal wind speed in knots - Isotachs

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting seminolesfan:
Dang, you quoted me JUST before i corrected it!!! LOL

You alright today fmet?


Yea, I'm great

I'm about to leave....be back this afternoon
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3164. IKE
Quoting HurricaneJoe:


I had a question... at 264 hours on the GFS, it had a large red circle next to the system with a 30 on it. Was that 30 knots of wind shear?


I've never understood what the 30 meant. I was going to ask on here, just never did???

What does that 30 mean?
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


She's an attractive basket-case.


lol
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting futuremet:


LOL

Maybe it was from met int the southern hemisphere
Dang, you quoted me JUST before i corrected it!!! LOL

(edit-and no, not from some upside down met, it was actually someone's high school earth science project)

You alright today fmet?
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3161. IKE
Quoting NJNorEaster:
Have to disagree with you Ike, I don't even finfd her all that attractive. Now Nicole Mitchell.... and she's a Hurricane Hunter...


Oh yes...Nicole.

Why did you have to bring her up? She's a doll.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
how much 90L resembles dean

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting IKE:
Looks like a high builds in in the GOM and blocks the southward movement of the trough, that it had earlier shown(previous days), diving down into the gulf-coast....it's not as pronounced a trough...



I had a question... at 264 hours on the GFS, it had a large red circle next to the system with a 30 on it. Was that 30 knots of wind shear?
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Have to disagree with you Ike, I don't even finfd her all that attractive. Now Nicole Mitchell.... and she's a Hurricane Hunter...
Member Since: Posts: Comments:
3157. IKE
Quoting futuremet:



Iky, maybe you were right about the GFS tending to degenerate trough in later runs.


I've followed these models...it did that on the recent one out in the central ATL...first showed it as a strong trough and then backed off. The backed off played out.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting seminolesfan:
archer312:



Does this help?

(I found it with google images. It looks cool but all the arrows are turning in the wrong direction!!!)


LOL

Maybe it was from met int the southern hemisphere
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3155. IKE
Here's what the GFS showed yesterday at the 12Z run. Note how strong the trough is....@ 204 hours...

Member Since: June 9, 2005 Posts: 23 Comments: 37858

Quoting IKE:
Looks like a high builds in in the GOM and blocks the southward movement of the trough, that it had earlier shown(previous days), diving down into the gulf-coast....it's not as pronounced a trough...



Iky, maybe you were right about the GFS tending to degenerate trough in later runs.
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Quoting IKE:
Bombs it in the inferno of the GOM....



I was just looking at that with my dad...it's almost as if the models are trying to make a Katrina situation again.
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Another South Florida landfall for the GFS.
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archer312:



Does this help?

(I found it with google images. It looks cool but all the arrows are turning in the wrong direction for the N hemisphere!!!)
Member Since: Posts: Comments:
3150. IKE
Looks like a high builds in in the GOM and blocks the southward movement of the trough, that it had earlier shown(previous days), diving down into the gulf-coast....it's not as pronounced a trough...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
3149. IKE
Quoting NJNorEaster:
And Stephanie Abrams is the worst. Did anyone see her Jenga explanation about wind shear and hurricanes?


She's an attractive basket-case.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
good morning everybody!!!

I would like to thanks you guys (especially StormW, Weather456, Ike ,etc...) for all your informations.
Like last year, Saint Martin/Sint Maarten is aim by those GFS map....
Anyway, what will be 90L next to the northern antilles?
Also, can someone tell me what will be the forecast for the 1st week of september, i have to live and leave my wife and baby kid here?
Merci beaucoups for your answer.
Keep in touch
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3147. IKE
Bombs it in the inferno of the GOM....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
And Stephanie Abrams is the worst. Did anyone see her Jenga explanation about wind shear and hurricanes?
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3145. IKE
Wow...10 days...actually 9.75 days...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
I don't know, but I have that bad gut feeling about 90L, especially with the continued consistency of the models not curving it out to sea.
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Thanks IcePilot for the info, that does help a little. Having worked on engines I understand your analogy, haha. So, in thinking about the cyclonic spin Inwards, and then Upwards, does help me with the conception of how the two spins could actually work together. I guess then the central low pressure core of rising air is picked up at high altitude by the anticyclonic clockwise spin and flung outwards up around the altitudes of the tropopause, maybe? Anyway, at high altitude, haha. Any more info appreciated, but I am starting to get the idea... Thanks
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Yeah that wake up with Al thing...i dont like it too much
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The weather channel is talking about edwards paternity scandal. What does that have to do with weather. NBC is killing the W Channel
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting archer312:
Thx NolesFan, that was helpful on the cyclone-anticyclone issue. Yes I know the anticyclone spins clockwise and the cylcone spins anticlockwise (confusing aint it?, haha). Seems funny because the anticyclone is high pressure, that is Descending Air, as I understand it. And the Cyclone is Low Pressure, hence Rising Air. If the Cyclone is on the bottom raising its air and the AntiCyclone is on the Top pushing its air downwards, then there must be a collision of sorts of all that air heading in opposite directions (up and down, as well as left and right spinning...???) Anyhow, that's what I just Dont Get about all this, very weird to me, how can this air-collision be Beneficial to storm formation and how can it Help Spin Up a storm..... Thanks, sorry for the long post.
Don't worry about post length. This is why I like the slower periods on the blog. You can actually talk to people and not just shout something out the car window while driving by. :)

Alot of the complexities of weather forecasting come down to all those airmass interactions that you are starting to see in your head. Most definitions and heck even charts work great in 2D, but when everything is in 4D (time is the 4th) it starts to get reallllyyy complex real fast.

One of our fellow bloggers has a YouTube video about cyclones and anticyclones that will give you some visuals to what we talked about. It's futuremet if you recognize the name.
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Sun just came up over the system: Link
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Quoting HurricaneJoe:


so what do you think its gonna do?


It is too early to tell, but the trend seems to be leaning west.
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As I thought: it did not recurve

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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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