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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Recon continues to find similar winds and slowly rising pressures with Don. This will be a 50mph tropical storm at landfall a bit south of Corpus Christi later this evening. This is not a big deal for Texas. I'm sure everyone down there is begging it to move towards them and give them some rain. Some folks will get it, but confined mostly to deep south Texas.
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What about the wave(? i don't know if it is a wave but a large area of disturbed weather) in the south central carribean, is it supposed to become anything because it looks like it may be moving NW but it looks as if part of the convection may split and form itself, jmo.
Member Since: July 25, 2011 Posts: 0 Comments: 453
342. 882MB
BESIDES THE NEW CMC SHIFTING WESTWARD WITH 91L THE HWRF IS SHOWING THE SAME THING!!
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Quoting ILwthrfan:
Look at the latest visible loops and you can clearly see two well defined llc's both west to east of each other. Pretty neat.

Link



I am expecting to see a burst of convection around that area later today.
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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


? Lol.
Member Since: July 15, 2006 Posts: 17 Comments: 10159
Quoting GHOSTY1:
here in NW houston we just got a pretty good heavy rainfall for about 15 minutes, i don't know what caused it could it be some moisture from Don is it just passing morning storms?


Looks like west of Anahuac might be on Don's extreme periphery, storms are coming from the SE. To the east, storms appear to be moving a different direction.
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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
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Quoting GHOSTY1:
here in NW houston we just got a pretty good heavy rainfall for about 15 minutes, i don't know what caused it could it be some moisture from Don is it just passing morning storms?
Just passing storms in Houston, they look to be moving in concert with Don, though. Take a look at your regional radar, you'll see what I am talking about.
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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
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Quoting ILwthrfan:
I agree. It's also got to moisten up it own atmosphere. I still think any development of this protential system will be slow and steady for 3 days out yet.


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:

Member Since: July 15, 2006 Posts: 17 Comments: 10159
Look at the latest visible loops and you can clearly see two well defined llc's both west to east of each other. Pretty neat.

Link

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UKMET Office


NEW TROPICAL STORM FORECAST TO DEVELOP AFTER 48 HOURS

FORECAST POSITION AT T+ 48 : 14.4N 51.9W



VERIFYING TIME POSITION STRENGTH TENDENCY

-------------- -------- -------- --------

12UTC 31.07.2011 14.4N 51.9W WEAK

00UTC 01.08.2011 14.4N 55.1W WEAK LITTLE CHANGE

12UTC 01.08.2011 15.0N 57.7W WEAK LITTLE CHANGE

00UTC 02.08.2011 15.7N 60.6W WEAK LITTLE CHANGE

12UTC 02.08.2011 16.2N 63.7W WEAK LITTLE CHANGE

00UTC 03.08.2011 17.0N 66.6W WEAK LITTLE CHANGE

12UTC 03.08.2011 17.6N 69.3W MODERATE INTENSIFYING SLIGHTLY

00UTC 04.08.2011 19.6N 71.3W WEAK LITTLE CHANGE

12UTC 04.08.2011 21.1N 74.3W WEAK LITTLE CHANGE



NEW TROPICAL STORM FORECAST TO DEVELOP AFTER 24 HOURS

FORECAST POSITION AT T+ 24 : 12.3N 80.9W



VERIFYING TIME POSITION STRENGTH TENDENCY

-------------- -------- -------- --------

12UTC 30.08.2011 12.3N 80.9W WEAK

00UTC 31.08.2011 12.6N 82.2W WEAK LITTLE CHANGE

12UTC 31.08.2011 12.8N 83.1W WEAK WEAKENING SLIGHTLY

00UTC 01.08.2011 12.1N 87.4W WEAK LITTLE CHANGE

12UTC 01.08.2011 12.0N 89.4W WEAK LITTLE CHANGE

00UTC 02.08.2011 13.3N 94.4W WEAK LITTLE CHANGE

12UTC 02.08.2011 12.0N 99.7W WEAK WEAKENING SLIGHTLY

00UTC 03.08.2011 13.4N 99.2W WEAK LITTLE CHANGE

12UTC 03.08.2011 BELOW TROPICAL STORM STRENGTH



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NotCircumventing, you really have a thing for Matagorda, don't you
Member Since: July 25, 2011 Posts: 0 Comments: 453
And the longer it takes 91L to organize, the more likely it is to head further west. This is going to be an interesting ride, that's for sure. And wow @ the shear in the Carrib.
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326. Gorty
Quoting SouthDadeFish:
NHC not getting very creative with their outlooks....


Almost seems like they are copy and pasting their previous outlooks lol.
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Don flopping again?




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Quoting MississippiWx:
91L has a very well-defined low level circulation and it's very easy to see on visible. It's also a huge area of disturbed weather. The size of the system and the elongated (West to East)orientation of the center will cause 91L to take its time becoming a tropical cyclone. I wouldn't expect a tropical depression until after late Saturday sometime:

I agree. It's also got to moisten up it own atmosphere. I still think any development of this protential system will be slow and steady for 3 days out yet.
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here in NW houston we just got a pretty good heavy rainfall for about 15 minutes, i don't know what caused it could it be some moisture from Don is it just passing morning storms?
Member Since: July 25, 2011 Posts: 0 Comments: 453
91L really hasn't changed much since this morning, except for the obvious and stated mileage covered, lol. Not to mention there is a Tropical storm approaching landfall which I am sure has most of their focus ATM.
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Quoting HurricaneSwirl:
Lol.

8AM:

1. A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1200 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT 15
TO 20 MPH.



2PM:

1. A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1150 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT
15 TO 20 MPH.


All they changed was 1200 to 1150 miles. That must have taken forever to come up with.


Crunching those numbers gives me 16 2/3 mph movement speed, in the Antilles within 2 days and 21 hrs
Member Since: August 30, 2008 Posts: 1 Comments: 224
Quoting HurricaneSwirl:
Lol.

8AM:

1. A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1200 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT 15
TO 20 MPH.



2PM:

1. A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1150 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT
15 TO 20 MPH.


All they changed was 1200 to 1150 miles. That must have taken forever to come up with.


ummm, yeah, they won't make a major change that far out except every 12 hours...takes too long to do and when it is still an invest and no eminant danger in next 24-48 hours it is a waste of time...it does show that it moved approximately 50 miles in 6 hours so it does show speed...
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317. JRRP
so 30%
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Eventhough 91L have lost some of the convection that was showing early this morning, it looks more organized and headed to warmer waters.
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Quoting P451:


I agree! Downright eerie!


Wow the GFS has gotten really advanced, shows deaths and even what type of animal they are before it even happens.
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Have a terrific vacation, Jeff!
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Quoting kwgirl:
No you are safe. They do have a weather bureau in the Caymans. Just be sure to watch the weather forcast so you aren't caught off guard. The storm, if it forms should be in PR by next Thursday.
Enjoy your trip and we'll see ya when you get back, if we all survive that is.
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Lol.

8AM:

1. A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1200 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT 15
TO 20 MPH.



2PM:

1. A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1150 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT
15 TO 20 MPH.


All they changed was 1200 to 1150 miles. That must have taken forever to come up with.
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Quoting jasonweatherman2011:
maybe adding a yellow mark soon at 8pm tonight!! look at the blue!! Caribbean


You have posted this repeatedly, enough already, we see it.
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91L has a very well-defined low level circulation and it's very easy to see on visible. It's also a huge area of disturbed weather. The size of the system and the elongated (West to East)orientation of the center will cause 91L to take its time becoming a tropical cyclone. I wouldn't expect a tropical depression until after late Saturday sometime:

Member Since: July 15, 2006 Posts: 17 Comments: 10159

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Quoting quakeman55:

No you be annoying. If you can't contribute anything constructive to the blog that is weather or tropics related, then please leave.


OK - that was just rude
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Hey guys check out my blog entry. I have been so busy with Calculus 2 this summer that I haven't had much time to do an in depth analysis in a good while! Hope you enjoy!

Link
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Quoting SouthDadeFish:
NHC not getting very creative with their outlooks....


Still using strong wording though.
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Quoting HurricaneDean07:
A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1150 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT
15 TO 20 MPH.


which means it would be the 5th named storm by end of July...that doesn't sit well with me for a prelude to the season....
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Quoting P451:


Lots of shear in the Caribbean. Tops really getting torn apart.



,ull interacting w/monsoon trough.....hows the wx been on the Hudson?
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A LARGE TROPICAL WAVE ACCOMPANIED BY A WELL-DEFINED LOW PRESSURE
SYSTEM IS LOCATED ABOUT 1150 MILES EAST-SOUTHEAST OF THE LESSER
ANTILLES. THIS DISTURBANCE CONTINUES TO SHOW SIGNS OF
ORGANIZATION...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR
GRADUAL DEVELOPMENT OVER THE NEXT FEW DAYS. THIS SYSTEM HAS A
MEDIUM CHANCE...30 PERCENT
...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT
15 TO 20 MPH.

still 30%
Member Since: August 30, 2008 Posts: 1 Comments: 224
NHC not getting very creative with their outlooks....
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Quoting blsealevel:
Carib. under some strong shear at present 20 to 30 kts



Atlantic storm is about the same right now but both areas i think is going to relax some in the next couple days as they move wnw

Invest 91L is under very little shear thanks to that Anticyclone located atop its circulation. Shear will be little to no problem for 91L.
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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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