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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Quoting HurricaneDean07:
Flwxchaser, umm right now there is no such thing as getting too much...


Ha ha - okay that's fair. I just meant I wasn't wishing a flood on ya.
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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.
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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


91L is under very low shear due to the upper level anticyclone directly on top of its low pressure.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
30% still.

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI JUL 29 2011

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM DON LOCATED ABOUT 120 MILES EAST-NORTHEAST OF BROWNSVILLE
TEXAS.

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.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER BEVEN
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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
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Flwxchaser, umm right now there is no such thing as getting too much...
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287. JRRP
Quoting P451:


I agree! Downright eerie!


that was good
LOL
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219 NotCircumventing "Over under on a Matagorda landfall?"

I've been making straightline projections of both NHC and ATCF numbers since the storm's crossover from the Caribbean to the Gulf of Mexico.
The landfall projections derived from its ATCF positions have never taken TS.Don north of (former)MatagordaIslandAirForceBase.
And those derived from consecutive NHC positions led to results too squirrelly (eg a projected landfall in the Yucatan followed by a projected landfall in Houston, etc) to be taken seriously.

I'll be posting a mapping soon, after the 6pmGMT ATCF numbers are released, and ya can take a look.
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Quoting P451:


I agree! Downright eerie!



ROFLMAO

My vote for BEST GRAPHIC EVER!!!!!!!!!
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Quoting NotCircumventing:
little swirl due east of OBX along 65W

Link

speed up loop

Hmm...wondering if that will do an a la Bret or Cindy...
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Don is certainly looking unimpressive - hopefully the "right" amount of rain for Texas. (Not too much, not too little)
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I'm thinking 91L may be a named storm by Sunday.
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from the looks of the latest fixes by HH, the storm head NW, then WNW, then just south of WNW, and it appears if it keeps its current motion Padre island is going to get a direct hit...
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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.
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Looks like don is peaked out will make landfall south of courpis christi with 50mph
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HURRICANE HUNTER AIRCRAFT REPORTS DON STILL HAS WINDS NEAR
50 MPH...

LOCATION...26.5N 95.6W
ABOUT 145 MI...235 KM SE OF CORPUS CHRISTI TEXAS
ABOUT 120 MI...195 KM ENE OF BROWNSVILLE TEXAS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 15 MPH...23 KM/H
MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES
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Well HH found 1006 MB on latest measurement, winds were found around 50 mph so that will stay the same, and the Recon is headed home...
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Quoting P451:


I agree! Downright eerie!



LOL dissipation date put it in the 13th bak tun!
Member Since: August 30, 2008 Posts: 1 Comments: 259
1:00 PM CDT Fri Jul 29
Location: 26.5°N 95.6°W
Max sustained: 50 mph
Moving: WNW at 15 mph
Min pressure: 1004 mb
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LOL p451!
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Quoting P451:


I agree! Downright eerie!



LOL.

You have too much free time.
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Quoting 2COOL:
I b cool!

No you be annoying. If you can't contribute anything constructive to the blog that is weather or tropics related, then please leave.
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264. 2COOL
I am only here to learn; been coming since '03. I appreciate much the comments here. I rarely ever comment, like to listen and learn. I just like to admit there are still variable we don't understand or know about. We are talking weather!
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Quoting Fleetfox:
New here, hello everyone. I'm in Houston, some thunder and rain moving through. Hope it all is heading to our friends in Austin.
So far it seems to all be staying well south. I think that Brownsville and surrounding areas, and our neighbors in Mexico will be getting it all.
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New invest possible near 35n,65ww
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258. 2COOL
I b cool!
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Quoting metwombly:
The models are unreliable for predicting invests and tropical waves. There needs to be a closed circulation and measurable winds for them to work, and even then they change from update to update.


Even after there is a storm, they have performed horribly.
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New here, hello everyone. I'm in Houston, some thunder and rain moving through. Hope it all is heading to our friends in Austin.
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Quoting ProgressivePulse:
The "Models" have done absolutely horrible with pre-storms this year, why would 91L be any different. Look at the satellites and observe, there will be a TD under your nose before you know it.
The models are unreliable for predicting invests and tropical waves. There needs to be a closed circulation and measurable winds for them to work, and even then they change from update to update.
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Quoting ldhall05:
Guys&Gals

Noobie here to the blog. I need your thoughts. I know it's really early on this Invest 91L But....... I'm taking the family to Grand Cayman leaving this Sunday 7/31/11. We are from Kentucky and praying for great weather. First half of next week looks good. We will be leaving the Caymans the following Sunday. Any thoughts on this developing Wave? Am i gambling here still going down?
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.
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Quoting NotCircumventing:
XTRP is always bullish on systems, it seems.


I've lost 10 lbs. XTRAP Weight Loss Model is predicting that, by the end of next year, I'll be completely gone.

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Quoting Seastep:
Uh-Oh. All models go through..... Herbert box.


I think the HERBERT box would be the dugout of a Little League game (hint: FG). But as for the Hebert box...heck, even the XTRP is not a model Model is going through it...this could be trouble...
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249. flsky
Not appropriate in this blog. You might get banned.

Quoting 2COOL:
How do you factor in peoples prayers? We've had a lot of them since '05. Also, for those of us who believe, how do you factor in Americas treatment of Israel? Just a thought.
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246. 882MB
HEY EVERYONE, HAVE YOU SEEN DA RECENT 12Z CMC MODEL RUN FARTHER WEST AND STALLS IT AT THE END WITH A RIDGE REBUILDING!!
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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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