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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As I thought: it did not recurve

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Quoting futuremet:
It will likely not curve out to sea in 06Z GFS, as it continues to erode the longwave trough.

Not with a ridge like this



so what do you think its gonna do?
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3135. IKE
90L is a large system. Looking at SSD visible on it.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting stoormfury:
FUTUREMET are you seeing the same thing i am seeing. a west or north of est track?


Yes, the models are definitely trending west.

This is how the GFS showed 18hrs ago (12Z yesterday).

the trough was obviously stronger. The image I showed in the previous post was at 156hrs. Since this one is from 18hrs ago.....156 18=174

174hr 12Z GFS

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So what do you think it will do?
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futuremet are you seeing the same thing i am seeing. a west or north of west track?
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It will likely not curve out to sea in 06Z GFS, as it continues to erode the longwave trough.

Not with a ridge like this

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06z GFS @ 132hrs.....

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although the models do give an indication of what might happen, one should never put 100% faith in them. in 2007 DEAn trck was for the leeward islands but it went thru the martinique / st lucia channel. in 2004 Ivan should have hit the cental winward islands and Barbados but instead ploughrd thru Grenada.
with tha approach od possible ANA i think even if the models are hinting of a leeward islands strike, the residents of the cental islands should monitor the movement of this system
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Quoting HurricaneJoe:
90L really seems to be getting its act together this morning. Developing some banding features as seen on this loop: Link


Im thinking TD later on today.
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90L really seems to be getting its act together this morning. Developing some banding features as seen on this loop: Link
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Quoting seminolesfan:
Sorry for jumping your case, F5. I'm sure you know the random comments we see here and I shouldn't have lumped you into "that" pile so quick.


Hey no problem, you were right about me not stating my material limitations, it gives everyone a false perception of my comments. I gtg its 4:14 WST and I am nearly unconsious... see you all at 12a.m. WST!
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Quoting archer312:
Thanks SeminolesFan and TxKeef for the replies. TxK, the link was a bit simplistic but thanks, did not really touch on the "reverse rotation" issue I am curious about, however. Thanks NolesFan also, if you have "more info" I am game, this "reverse spin helping" has never been clear to me, it seems that it would Hurt rather than Help to have a spin in the other direction right on top of a Low Level Circulation, haha. Or am I missing something. (by the way, NolesFan... shouldn't you be a
Hurricanes Fan on this blog, haha??!)
Thx for your help


Think of it as a one cyl vs a two cyl engine. The direction of spin is caused by coreolis - inward to a center is counter clockwise and movement outward from a center point is CW (in N hemishere). Therefore if a low pressure area (air moving CCW inward) has a anti cyclone above it then it has "help" or suport in moving the air outward at the top. That is the second cyl of the "engine". If you look at sat pics of a 'cane, the high level (top) cloud layers rotate clock wise and away from the center.
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3124. tkeith
Quoting HurricaneJoe:


Good morning everyone

What model is that tkeith?
Unisys GFSx 500mb
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one thing is for sure this morning, 90l has certainly has a faster forward motion. A faster storm may mean no recurve at all this is all a timing game. Next week is going to be very long I can tell you guys that!
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Quoting tkeith:


Good morning everyone

What model is that tkeith?
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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.
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Quoting F5Tornado:







Thanks all, I am only 12 years old, and I am still learning about Warm Core Barotropic Lows... in fact, I am still learning about Diadibatic lifting, so this info is great to expand my intelligence

By the way

I was looking for info, thats why I asked, I only have bits and peices of info, did I forget to mention it was my opinion??? It was a conversation starter, thats all. But your right, I should have stated the limitation of my material.

I gtg in a sec.
Sorry for jumping your case, F5. I'm sure you know the random comments we see here and I shouldn't have lumped you into "that" pile so quick.
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Tropical Update
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting tkeith:
This is not 90L is it?
Yup.
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Quoting CybrTeddy:


90L has WAY different conditions. Less dust because of TD-2 sweeping it away. Less shear because of an Anti-cyclone. Plus 90L is about x6 bigger than TD2.


Quoting Weather456:


in tropical met, models are seldom used to calculate rainfall since actual rainfall in hurricanes surpasses the threshold of some models.


Quoting jipmg:


yes models are somewhat consistent with its 3-4 day track..



Thanks all, I am only 12 years old, and I am still learning about Warm Core Barotropic Lows... in fact, I am still learning about Diadibatic lifting, so this info is great to expand my intelligence

By the way
Quoting seminolesfan:
I have an 'anouncment' for the uninformed. It is not a good start to a post looking for "charts and links" to have a know it all attitude going full blast. It kinda make you look silly. If you have the info on TD2 why do you need my goodies.


I was looking for info, thats why I asked, I only have bits and peices of info, did I forget to mention it was my opinion??? It was a conversation starter, thats all. But your right, I should have stated the limitation of my material.

I gtg in a sec.
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3116. tkeith
This is not 90L is it?
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3115. tkeith
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Quoting archer312:
Thanks SeminolesFan and TxKeef for the replies. TxK, the link was a bit simplistic but thanks, did not really touch on the "reverse rotation" issue I am curious about, however. Thanks NolesFan also, if you have "more info" I am game, this "reverse spin helping" has never been clear to me, it seems that it would Hurt rather than Help to have a spin in the other direction right on top of a Low Level Circulation, haha. Or am I missing something. (by the way, NolesFan... shouldn't you be a
Hurricanes Fan on this blog, haha??!)
Thx for your help
Yeah, I looked at the link myself and wasn't very blown away.

Don't worry too much about the direction of spin. Think of high pressure as air moving out from the high.

A tropical cyclone is made up of organized convection pushing air up into the atmosphere. If there is a high on top of a TC then that high has air moving outward. It vents the air the convection is moving upward and pushes it outward and in the process makes room for further upward movement of air.

The reason it is an anticyclone is because it is a high pressure area aloft. All highs spin clockwise, so they are anticyclones.
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3113. tkeith
this isn't pretty...
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3112. jipmg
Quoting CybrTeddy:


90L has WAY different conditions. Less dust because of TD-2 sweeping it away. Less shear because of an Anti-cyclone. Plus 90L is about x6 bigger than TD2.


90L also has quite a good amount of convection in and around the center of circulation
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Quoting F5Tornado:
I have an anouncment for the uninformed. TD2 has died. Sad, sort of, couldn't beat wind shear and win against El Nino..... Its soon to be TD3 will most liekly get the same conditions. It is powerful, however, and could make it if it goes really fast.... then again it would shear itself apart if it was not organized enough... I hope we at least see a non East Coast threatining System.... Could anybody give me a current chart or link please? Thanks.


90L has WAY different conditions. Less dust because of TD-2 sweeping it away. Less shear because of an Anti-cyclone. Plus 90L is about x6 bigger than TD2.
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Quoting F5Tornado:


What? 6 inches of rain by Aug 9???? They had better be getting the calculations right... a major hurricane producing 6-7 inches of rian in soem locations?? Are there other models lke this?


in tropical met, models are seldom used to calculate rainfall since actual rainfall in hurricanes surpasses the threshold of some models.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
I have an 'anouncment' for the uninformed. It is not a good start to a post looking for "charts and links" to have a know it all attitude going full blast. It kinda makes you look silly. If you have the info on TD2 why do you need my goodies.
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3108. jipmg
Quoting F5Tornado:


What? 6 inches of rain by Aug 9???? They had better be getting the calculations right... a major hurricane producing 6-7 inches of rian in soem locations?? Are there other models lke this?


yes models are somewhat consistent with its 3-4 day track..
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Thanks SeminolesFan and TxKeef for the replies. TxK, the link was a bit simplistic but thanks, did not really touch on the "reverse rotation" issue I am curious about, however. Thanks NolesFan also, if you have "more info" I am game, this "reverse spin helping" has never been clear to me, it seems that it would Hurt rather than Help to have a spin in the other direction right on top of a Low Level Circulation, haha. Or am I missing something. (by the way, NolesFan... shouldn't you be a
Hurricanes Fan on this blog, haha??!)
Thx for your help
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Quoting Weather456:
The GFDL also intensify 90L to major hurricane



What? 6 inches of rain by Aug 9???? They had better be getting the calculations right... a major hurricane producing 6-7 inches of rian in soem locations?? Are there other models lke this?
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if the GFDL is correct then we in the islands are in serious trouble
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I have an anouncment for the uninformed. TD2 has died. Sad, sort of, couldn't beat wind shear and win against El Nino..... Its soon to be TD3 will most liekly get the same conditions. It is powerful, however, and could make it if it goes really fast.... then again it would shear itself apart if it was not organized enough... I hope we at least see a non East Coast threatining System.... Could anybody give me a current chart or link please? Thanks.
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that is correct. if the turn is not seen with exTD2 then the indications are that 90L will continue west or north of west for a few days
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The GFDL also intensify 90L to major hurricane

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting stoormfury:
The track of the remnants of TD2 could be an indicator for the path of 90l


Yea, but 90L is much more south than TD2.
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The track of the remnants of TD2 could be an indicator for the path of 90l
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3099. TxKeef
Quoting archer312:
Good Morning, Storm Buffs-

Question: I have never understood the deal with the Anti Cyclone building On Top of the opposing cyclonic rotation below, and how that even works, much less how it actually Helps a Tropical Cyclone to build... seems to be something to do with reducing the effect of Wind Shear on the the TC, maybe. If so, how so, any clarity here would be helpful. Thx.



http://www.scienceclarified.com/Co-Di/Cyclone-and-Anticyclone.html


Try that out.
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Florida NWS discussions

Nothing too earth shattering. Tallahasee and Miami were the ones to speak of 90L the most.
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Quoting archer312:
Good Morning, Storm Buffs-

Question: I have never understood the deal with the Anti Cyclone building On Top of the opposing cyclonic rotation below, and how that even works, much less how it actually Helps a Tropical Cyclone to build... seems to be something to do with reducing the effect of Wind Shear on the the TC, maybe. If so, how so, any clarity here would be helpful. Thx.
It's more about the anticyclone having air moving outward from the center of it. This allows the lower level cyclone to 'breathe'.
(I can give you more on this if you want. Didn't want to jump right in with more info than you wanted/needed.)
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SHIPS makes 90L a monster.
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central atlantic view noaa site has the visiable available first
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Good Morning, Storm Buffs-

Question: I have never understood the deal with the Anti Cyclone building On Top of the opposing cyclonic rotation below, and how that even works, much less how it actually Helps a Tropical Cyclone to build... seems to be something to do with reducing the effect of Wind Shear on the the TC, maybe. If so, how so, any clarity here would be helpful. Thx.
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3093. 7544
Quoting Cotillion:
And the burst of convection on ex-TD2 has died down again, it just can't get much going.


still taking in all the dry air infront of it you see it here

Link
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3092. jipmg
Quoting leftovers:
first visiable of 90 seems like the feeder bands are pointing wnw indication of its movement hope so


link

I cant get much out of the NOAA site
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first visiable of 90 seems like the feeder bands are pointing wnw indication of its movement hope so remember early forecasts for this yr were calling for a recurve yr
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And the burst of convection on ex-TD2 has died down again, it just can't get much going.
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Quoting mobilegirl81:
GFS turned it back into a MISS/ALA storm. WE are probably going to see it jump east,west,east,west again.
It looks like the GFS is the outlier on the trough being weaker and the subtropical ridge being stronger. The GFDL/HWRF/CMC have the ridge breaking down quite a bit further east. But like you're saying, that's this run. Things will shake back and forth for a while and we're just looking for trends and patterns.
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Quoting CybrTeddy:


Yessir.


Then for sure, that'll help!

The Euro may make it slower too because it's not hinting at as strong of a high as the GFS is.

Both are pushing the centre (maybe because of the trough?) off towards the Azores though.
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Quoting Cotillion:


All the way with it?


Yessir.
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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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