Don closing in on Texas; 91L a potential threat to the Lesser Antilles

By: Dr. Jeff Masters , 3:22 PM GMT on July 29, 2011

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Tropical storm warnings are flying along the coast of Texas from Brownsville to Matagorda as Tropical Storm Don closes in on the Texas coast. Don remains a disorganized, moderate strength tropical storm, and appears unlikely to cause major damage or bring much-needed drought-busting rains to Texas. A hurricane hunter plane is in Don, and found highest surface winds of 55 mph at 11:06am EDT. Don continues to have trouble with moderate wind shear of 10 - 20 knots, which is injecting dry air to the northwest into the storm. Water vapor satellite images show this region of dry air to the northwest of Don. Visible satellite imagery from this morning shows little change to Don so far today, with most of the heavy thunderstorms on Don's south side, and the cloud pattern elongated, the sign of a storm struggling with wind shear. Radar out of Brownsville, Texas shows the main rain areas are on the south of Don's center, and bands of heavy rain are now very close to the Texas/Mexico border.


Figure 1. Morning image of Tropical Storm Don from the Brownsville, Texas radar.


Figure 2. The latest drought map for Texas shows that over 75% of the state is in exceptional drought--the highest category of drought. Image credit: U.S. Drought Monitor.

Forecast for Don
The wind shear and dry air affecting Don will continue until landfall, and it is unlikely Don will intensify to more than a 60 mph tropical storm. With most of the heavy thunderstorms displaced to the south side of the storm, Mexico will be the primary beneficiary of Don's expected rains of 3 - 5 inches. South Texas will see modest rains of 1 - 2 inches over a few isolated areas, but Don is going to do very little to bring drought relief to the state. Most of Don's rains in Texas will be concentrated in the extreme southern portion of the state near Brownsville. This portion of Texas is experiencing only moderate drought, and the extreme to exceptional drought areas of the state will miss the bulk of Don's rains.

For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast. The 11 am version of this forecast shows that Corpus Christi Texas has the highest chance of tropical storm-force winds (39+ mph): 48%. The primary threat from Don will be heavy rain, which will caused localized flooding problems. An isolated tornado is also a possible concern.


Figure 3. Morning satellite image of 91L.

African wave 91L a potential threat to the Lesser Antilles
A well-organized African wave near 9°N 44°W (Invest 91L) is headed west-northwest at 15 - 20 mph, and could arrive in the vicinity of the Lesser Antilles Islands as early as Monday night. Residents of the Lesser Antilles should pay careful attention to this system, as it has the potential to organize into a tropical storm before reaching the islands. While visible satellite loops currently show only minimal heavy thunderstorm activity and no signs of a surface circulation, there is a pronounced large-scale rotation to the cloud pattern. Water vapor satellite loops show that a large area of dry air from Africa lies just to the north of 91L, and this dry air is inhibiting development. The SHIPS model is diagnosing low shear, 5 - 10 knots, over 91L, but the University of Wisconsin CIMSS analysis shows that moderate shear, 10 - 20 knots, is affecting 91L. Sea surface temperatures are 27.5° - 28°C, which is 1° above the 26.5°C threshold usually needed to support a tropical storm.

Forecast for 91L
Low to moderate wind shear of 5 - 15 knots is predicted along 91L's path over the coming three days, which should allow the storm to steadily organize, assuming it can shut out any incursions of dry air that might intrude. The latest 06Z run of the GFS model does show 91L developing into a tropical storm by Monday, but the other three most reliable models for forecasting formation of a tropical storm--the ECMWF, NOGAPS, and UKMET models--show little or no development of 91L in their latest runs. On Monday, when most of the models predict that squalls of rain from 91L will begin affecting the Lesser Antilles, wind shear is expected to rise to the moderate or high range, which should act to interfere with development. The latest runs of the GFDL and HWRF models show 91L developing into a hurricane by Monday, but these models are not to be trusted for systems that have not developed into a tropical depression yet. The long-range path of 91L could take it through the Caribbean or towards the U.S. East Coast; it is too early to know with path might be more probable. NHC is giving a 30% chance that 91L will develop into a tropical depression by Sunday morning.

Iran records its hottest temperature of all-time
Omidieh, Iran and Shoshtar, Iran hit a scorching 52.6°C (126.6°F) on July 27, the hottest temperatures ever recorded in the country. The previous record was 52.5°C (126.5°F) set in Hamidiyeh on August 4, 2001. If confirmed by the Iranian weather service, these readings would rank as the third hottest undisputed temperatures ever measured in Asia. There have been only two Asian readings matching or exceeding Wednesday's new Iranian record of 52.6°C that are undisputed that I am aware of. Both of these occurred last year, and were recognized by their respective country's meteorological services as new official records for their country:

53.5° (128.3°F) in Moenjodaro, Pakistan on May 26, 2010
52.6°C (126.7°F) in Abdaly, Kuwait on June 10, 2010

Iran is the third nation this year to set a new all-time heat record (no nations have set an all-time coldest temperature record this year, or did so in 2010.) The Democratic Republic of the Congo, the world's 12th largest country, set a new all-time extreme heat record on March 8, 2011, when the temperature hit 39.2°C (102.6°F) at M'Pouya. Congo's previous all-time hottest temperature was 39.0°C (102.2°F) at Impfondo on May 14, 2005.

Also this July, a 50.2°C temperature was measured at Aydyngkol Lake, China--the highest temperature on record at any official Chinese weather station. Next week, our weather historian, Christopher C. Burt, will report on this record. Credit for researching these records goes to weather records researcher Maximiliano Herrera, who maintains a comprehensive set of world extreme temperature records on his web site.

Vacation
I'm taking some time off today through August 9 for a family celebration and vacation, and don't plan on blogging again until August 10 unless a major hurricane develops. In my absence, Angela Fritz will be handling most of the blogging duties, and she will have a post on the latest for Don this afternoon. Angela is on Pacific time, so her posts will be later in the day than I make them.

Jeff Masters

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Mexico is having a drought too, but not quite as severe as texas is going through and they got some slight relief from TS Arlene.
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting barbamz:


Maybe this one? Got it from this blog few days ago:
http://www.canefever.com/#!links



That isn't the link I was looking for but it will be fun to check it out as well! Thank you very much for posting it.
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Quoting EyeWonder:
Here in Barbados the local Met Office have issued a special weather bulletin regarding what is now a "strong tropical wave" that has the potential to stengthen. We should feel its effects late Sunday night into Monday.
Guess we should be having a wet Kadooment.
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Quoting P451:


Good find.

Like Bret and Cindy ?
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It is a shame that most of the rainfall with Don may go into Mexico, as I know Texas really needs the rain. I don't know how bad Mexico needs the rain, but I do not figure they need it as much as Texas considering they have had several landfalling tropical systems over the past couple of years.
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Quoting xcool:



12z Euro 96 hours


Is that the next new system thats west of the lesser antilles? what is the name of the f storm? (Fiona?)
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting P451:


Ah, well, he had an answer for that, too LOL






So i guess we should all just hang it up and follow Levi's orders for fear of being redundant?
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Quoting jasblt:


You have posted this repeatedly, enough already, we see it.


He made like 20 different handles. Put him on ignore, he's just trying to get some attention.
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381. xcool



12z Euro 96 hours
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting ProgressivePulse:



As stated in Dr. Masters blog, the HWRF and GFDL cannot be trusted until a tropical depression has formed.


even then they need ankle monitors.
Member Since: August 29, 2010 Posts: 0 Comments: 5236
From the Blog

The latest runs of the GFDL and HWRF models show 91L developing into a hurricane by Monday, but these models are not to be trusted for systems that have not developed into a tropical depression yet.
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if the two rotations combine will it be a negative impact for the invest or will be good?
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting P451:


Good find.



Why do I feel like saying "Peek A Boo" when looking at that, lol.
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Here's my blog update on Don and 91L.
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Quoting MississippiWx:


Lol...It's amazing how the HWRF and GFDL can go from one extreme to the next. It seems that the quality of those two models has decreased over time.



As stated in Dr. Masters blog, the HWRF and GFDL cannot be trusted until a tropical depression has formed.
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GFDL drops 91L HWRF takes it more west
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Quoting MississippiWx:


Lol...It's amazing how the HWRF and GFDL can go from one extreme to the next. It seems that the quality of those two models has decreased over time.


Those models are past their prime. They will have to start being in info-mercials to pay the bills.
Member Since: August 29, 2010 Posts: 0 Comments: 5236
.
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what in the heck is goin on here, Looks like another rain band may be off the coast, i didnt know the bands extended this far north (these bands look as if to be part of Don with the spin) but it would be our luck that it dies out before reaching anywhere or just sprinkles the area
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting MississippiWx:


Well, the moisture associated with the wave isn't too bad right now. The SAL north of the wave could slow development some, but not until the surface low deepens enough for it to ingest some of that air into its circulation. For now, it's just going to spend its time bundling all of that energy into one cyclone:



SAL not that bad. Might slow it down some but with all the moisture there shouldn't hinder it too much.
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Quoting MississippiWx:
91L resembles a developing Western Pacific typhoon:

Another very large system that takes it's time to spin up. Unfortunately, should conditions be conducive, there isn't much that can stop it.
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365. Jax82
Just wait until a model shows 90L hitting anywhere in FL, this blog will go WILD.
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Quoting FLWxChaser:
I guess it's good it's Don and not Dawn otherwise she'd get a ticket for being topless:



More like special marine warning Don.


lol, that was a good one
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting JRRP:
PLOP!!!!!!!!!!
GFDL
Link


Lol...It's amazing how the HWRF and GFDL can go from one extreme to the next. It seems that the quality of those two models has decreased over time.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
HWRF is not updated yet however, pretty good consensus on the short term track thus far.



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12z CMC

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360. JRRP
PLOP!!!!!!!!!!
GFDL
Link
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Quoting GHOSTY1:
NotCircumventing, you really have a thing for Matagorda, don't you


Who doesn't?....their redfish are huge!
Member Since: August 29, 2010 Posts: 0 Comments: 5236
I guess it's good it's Don and not Dawn otherwise she'd get a ticket for being topless:



More like special marine warning Don.
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Quoting KittyTwister:
I know this is a shot in the dark, but a few weeks ago someone here on this blog posted a link to what I think was his blog. Once clicked it led to a page that seemed to have hundreds of other weather related links, basically just a link page. Does anyone here have any idea what I am speaking of? If so please can you please help me find it again?
TIA


Maybe this one? Got it from this blog few days ago:
http://www.canefever.com/#!links
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Quoting MississippiWx:
91L resembles a developing Western Pacific typhoon:



Alex....
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting P451:


Well, Levi touched on this in the previous blog this AM, so here's your answer:



Was commenting on the 1006, highest yet.
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91L resembles a developing Western Pacific typhoon:

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting ProgressivePulse:
Don flopping again?





I was going to say, any movement N of the forecast track means a big difference in how much rain any given Texan gets. Austin has only a 20% chance over Don's life, and
that seems a little low.

Much better to be pleasantly surprised than utterly disappointed again, I suppose.
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we have 95E in the east pacific. cmc 12z shows the ridge rebuilding meaning no recurvuture.. thoughts anybody?
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349. JRRP
HWRF
Link
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Quoting tiggeriffic:
91L already organizing...and from the size of it now (bigger than Don was) it could create its own environment and pull itself in and tighten up when it really begins to strengthen...remember...where it is has several hours more of daylight than the east coast...they are behind us time wise...so when we would be thinking the sun is down and it may weaken a bit...it still has day light and heat to fire up


Uh, the further East you go, the further ahead they are in time until you hit the dateline...
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Quoting NotCircumventing:
334,

Watchoo talkin 'bout, Tigger?


easy...a large invest can avoid dry air in its core due to its massive size...the outer bands protect the core...as the core gets stronger it pulls that energy inward...hence compacting in size and getting stronger...look at Andrew compared to Hugo...Hugo was MASSIVE in size...and upto the time it hit he was the costliest hurricane to ever hit...then came Andrew...tiny in comparison...yet more costly damages wise...
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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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