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 Drakoen:
The first thing to pull it northward is a shortwave trough then a big longwave trough advects down from Canada:


That's the key... if that first shortwave is strong enough it will cause to go through the Islands, else if its not deep enough then it should shave the southern Greater Antilles...
Member Since: August 14, 2008 Posts: 4 Comments: 5038
385. 900MB
Hey all! Long, long time. I lurk but tend to keep my mouth shut and keep it to the experts.
Just my 2 cents: TD2 Has a prayer, but with 90L it is we that should be saying our prayers- this could be the first major of the season, especially with TD2 sucking in the dry air north, clearing the deck for 90L.
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Quoting Patrap:


Ill be doing the same this evening as well Chief..

Your first as your Senior to me.
i be listening as well tonight boys the show should be interesting
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381. IKE
Quoting Acemmett90:

maybe it because i have a bad feeling about this storm i am useally not like this


Assuming you live in the USA....It's close to FOUR thousand miles away from the USA.

Member Since: June 9, 2005 Posts: 23 Comments: 37860
navy will proably post up a TCFA within next 6 to 12 hrs depends on performance and at the moment looks like all systems are go for 90l dev.
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Quoting Drakoen:
I wonder if they will upgrade to red...


I think they might in the next TWO.
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Quoting StormW:
Back later tonight.

Gonna try to call in to the Barometer Bob show.


Ill be doing the same this evening as well Chief..

Your first as your Senior to me.
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The first thing to pull it northward is a shortwave trough then a big longwave trough advects down from Canada:
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Quoting Vortex95:


Possibly when convection gets to the center. Anyways, I doubt anyone actually remembers but wasn't fay in orange just before it developed?


wasn't TD2?
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371. IKE
12Z GFS at 162 hours...




6Z GFS at 168 hours...

Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting Drakoen:
I wonder if they will upgrade to red...
they will likly go to high chance at 2 tonight is the first night out convective activity over open water by 11 pm or there after edt could be quite interesting we are a witness to the birth of the storm
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Quoting Patrap:




Erm... I forgot an "as." It should read "...because there is not as much mixage..."
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Quoting weatherwatcher12:

I believe K-Man said that it is just upper diffluence caused by interaction with the ULL


Difluence or not it will be more energy going into the GOM this weekend.
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Quoting hurristat:


in this case 100%. LOL.


LOL ..hindsight is 20/20. ;)
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has anyone taken a scale on this thing... Its circulation is absolutely huge!
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Quoting hurristat:


I heard about this on the radio. This has nothing to do with satellites. When a hurricane hits the coast, it mixes up the dirt. So by taking core samples from the coasts, you can see how often hurricanes hit. Therefore, because there has not been much mixage in the lower levels, this has been the most active period in a long time.


There is PLENTY of evidence of Past Hurricane buried deep in the Ground in Se. La.
Here the Corps of enginneers found after Katrina in core samples,a layer of peat and cypress that was from a Storm Larger Than Katrina about 400 years ago,and that is also recorded in Indian History past down from Gen to Gen.



Page 1
Geologic Conditions Underlying the 2005 17th Street Canal
Levee Failure in New Orleans
J. D. Rogers, M.ASCE


Abstract: A careful program of subsurface sampling and cone penetration test soundings was employed to characterize the geologic
conditions beneath the failed portion of the 17th Street Canal levee in New Orleans, where a 150 m long section of the levee and floodwall
translated up to 16 m when flood waters rose to 1–2 m of the wall’s crest on August 29, 2005, during Hurricane Katrina. The subsurface
conditions are characterized by discrete layers of fill placed upon the historic cypress swamp, which is underlain by a deeper, prehistoric
cypress swamp. These swamp deposits were consolidated beneath the levee, and in the area of the 2005 failure, the swamp materials
infilled a natural depression believed to be an old slough, which dipped below the sheetpile tips for a distance of about 50 m, which
corresponds to where the breach appears to have initiated. Detailed examination of the recovered soils suggest that recent hurricanes
periodically inundated the swamps with saline and/or brackish water, which cause a mass dieoff of swamp vegetation and flocculation of
suspended clays, due to the sudden increase in salinity. These conditions promote deposition of discontinuous clay seams beneath layers
of organics, which are then covered by fresh water swamp deposits. This sequence is repeated, like a series of tree rings, throughout the
swamp deposits. The cypress swamp deposits lying beneath the levee also exhibit high hydraulic conductivity. These materials contain
corky wood, and recovered samples often exhibited densities less than water. Nine of the post-Katrina borings recovered intact samples
of a basal rupture surface comprised of organic silty clay exhibited near zero residual shear strength after shearing 80 to 100 mm
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Quoting rwdobson:
@334, I've dug sand cores in the delmarva peninsula and you could definitely tell when a big storm came by, from the layers of gravel overwash. I'm not sure how you can tell the difference between a hurricane and a nor'easter storm, though. maybe the sedimentologists can; i know we had people there taking very detailed measurements of every layer of sand, including the angle of the grains etc.
Wonder how much of the shore line from Hatteras, down to the Keys up west side of Florida, across the the northern shore of the GOM, back down the east coast of Central America and of course the islands of the Caribbean and Bahamas - was covered. Do not remember any media coverage of the sampling here in the lowcountry of SC, but I could have missed it.
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drak yes 90L is organising a bit. also the12Z gfs continues to put the system in the central islands by tuesday week
Member Since: August 22, 2006 Posts: 0 Comments: 2722
Quoting TreasureCoastFl:

yeah, I guess I was still reading it when it was posted by someone else. What were the odds of that happening?


in this case 100%. LOL.
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Quoting jasoniscoolman10:
here is a WEATHER map of 90L


Looks like there's a little interaction between 90L and 2L.
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I wonder if they will upgrade to red...
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Quoting hurristat:


A little late to the chase, here... LOL

yeah, I guess I was still reading it when it was posted by someone else. What were the odds of that happening?
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Quoting chevycanes:

dropping like a rock? surely you're joking?

dropping like a rock is when pressures drop by at least 10 MB's in a few hours.


Like Wilma!
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Quoting Acemmett90:

facts pressures droping like a rock and its getting better organised and almost all of the modle are projecting a florida hit


Can you name which models are projecting a Florida hit? Do you know how inaccurate models are this far out, not only for intensity, but for track as well? Look, its obvious you're new at this whole tracking thing. Study guys like StormW, Drak, Hurricane23, or Kori for their level headed analysis and learn from them. This blog is full of knowledge, and its best to just read than post often misleading doomcast scenarios.
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Quoting chevycanes:

what about all the fish storms that don't hit land?


They don't know. But usually, the amount of storms that hit land is directly proportional to the amount of total storms.
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Quoting FloridaTigers:
Interesting BBC article: http://news.bbc.co.uk/2/hi/science/nature/8197191.stm

Hurricanes in the Atlantic are more frequent than at any time in the last 1,000 years, according to research just published in the journal Nature.

oh! I just posted the NY Times article. Didn't see you did the same one. JINX! lol
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Quoting Acemmett90:

facts pressures droping like a rock and its getting better organised and almost all of the modle are projecting a florida hit

dropping like a rock? surely you're joking?

dropping like a rock is when pressures drop by at least 10 MB's in a few hours.
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@341 fact: the model predictions at this time frame have huge margins of error and minimal forecast skill.
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Quoting PennGator:
#2 center totally exposed as shown on rgb


Shear is blowing that big blow up of thunderstorms away from the COC in a hurry.
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Quoting TreasureCoastFl:
Today's NY Times article on storm study for anyone interested:

http://www.nytimes.com/cwire/2009/08/13/13climatewire-study-finds-big-storms-on-a-1000-year-rise-94 323.html


A little late to the chase, here... LOL
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@334, I've dug sand cores in the delmarva peninsula and you could definitely tell when a big storm came by, from the layers of gravel overwash. I'm not sure how you can tell the difference between a hurricane and a nor'easter storm, though. maybe the sedimentologists can; i know we had people there taking very detailed measurements of every layer of sand, including the angle of the grains etc.
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Quoting hurristat:


I heard about this on the radio. This has nothing to do with satellites. When a hurricane hits the coast, it mixes up the dirt. So by taking core samples from the coasts, you can see how often hurricanes hit. Therefore, because there has not been much mixage in the lower levels, this has been the most active period in a long time.

what about all the fish storms that don't hit land?
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Today's NY Times article on storm study for anyone interested:

http://www.nytimes.com/cwire/2009/08/13/13climatewire-study-finds-big-storms-on-a-1000-year-rise-94 323.html
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Quoting FloridaTigers:


Nervous? Please, its a just an INVEST. Quit being the JFV Jr. Team and look at the facts. The storm, not even a depression, is still thousands of miles away


It's time to coin a new term for those who keep thinking of the worst possible scenario: Doomcasters.
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Quoting Acemmett90:

now im nervous and you should be to i hope i goes poof but i know that wont happen


Nervous? Please, its a just an INVEST. Quit being the JFV Jr. Team and look at the facts. The storm, not even a depression, is still thousands of miles away
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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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