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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Even Brian Norcross was surprised. He guessed the circulation near Brownsville is the mid level, and the one s of Corpus is the low level one. To me it looks like its reforming near Brownsville.
Quoting hurricanejunky:
How about that mesocyclone that's formed in Don just east of Brownsville? Looking at radar it's really pronounced! Is that common? I've not seen that before that I can remember.
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Quoting Gearsts:
based on what?i dont understand:/

Because every time doc leaves on vacation, a new system always develops.
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tgif
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Quoting bamagirl1964:
Hello Everyone! I have been fascinated with reading the blog for years, but have never posted a comment, so here goes! I live on the beautiful Gulf Coast in Mobile, Alabama. I have been watching 91L with some interest and I would like to pose a thought. We had Major Hurricane Frederic back in 1979 and as I am watching 91L, I cannot help but notice it is in the exact same place as Frederic was! I realize there are many factors that come into play with a potential hurricane so far out, but our area is overdue and I cannot help but be concerned. Do any of you remember Hurricane Frederic? Thank you for allowing me to join in the blog and I look forward to hearing from y'all! :)


Nope can't say I remember Frederic. But I was only 4 then so I guess maybe I shouldn't. And you are right I'm afraid we're due on the northern gulf coast. We've not had a visit since Gustav and Ike.
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Meh.


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Quoting TXEER:
What is the difference between the "computer models" and the "ensemble models"?

models is difference to emsemble
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Quoting MiamiHurricanes09:
Yup, based on that the NHC should already start initiating advisories on 91L FWIW.
based on what?i dont understand:/
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I live in P.R. and I want some thoughts about your predictions for 91L in terms of the Northen Islands.
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Hey bamagirl.  Here is the track for Frederic from 79...  Welcome to the blog.  These guys and gals are VERY knowledgeable and friendly:)


Member Since: June 12, 2006 Posts: 1 Comments: 600
Quoting P451:
It's coming straight at me.



I'm about to get my ass kicked. For reference about half way down the wider part of the Hudson, east side of the river.

Huge bolt of lightning just rocked the neighborhood real bad.

Apparently this thing is putting out 2500 strikes in 15 minutes (at least according to a local news report, I'm wondering if that's per hour).

You step outside, your hair starts to stand out. I think I'll stay inside.



Stay safe, i have the strongest rotation a tad to the north of New City and Congers
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Quoting bamagirl1964:
Hello Everyone! I have been fascinated with reading the blog for years, but have never posted a comment, so here goes! I live on the beautiful Gulf Coast in Mobile, Alabama. I have been watching 91L with some interest and I would like to pose a thought. We had Major Hurricane Frederic back in 1979 and as I am watching 91L, I cannot help but notice it is in the exact same place as Frederic was! I realize there are many factors that come into play with a potential hurricane so far out, but our area is overdue and I cannot help but be concerned. Do any of you remember Hurricane Frederic? Thank you for allowing me to join in the blog and I look forward to hearing from y'all! :)
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835. TXEER
Quoting PensacolaDoug:



Ensemble models are the same models ran multiple times with slightly differnt initial conditions and peramiter tweaks. Or something like that...


Thank you!
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How about that mesocyclone that's formed in Don just east of Brownsville? Looking at radar it's really pronounced! Is that common? I've not seen that before that I can remember.
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Quoting RitaEvac:
Masters is out and that in itself is a sign
Yup, based on that the NHC should already start initiating advisories on 91L FWIW.
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Member Since: July 12, 2011 Posts: 0 Comments: 1532
Masters is out and that in itself is a sign
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Hello Everyone! I have been fascinated with reading the blog for years, but have never posted a comment, so here goes! I live on the beautiful Gulf Coast in Mobile, Alabama. I have been watching 91L with some interest and I would like to pose a thought. We had Major Hurricane Frederic back in 1979 and as I am watching 91L, I cannot help but notice it is in the exact same place as Frederic was! I realize there are many factors that come into play with a potential hurricane so far out, but our area is overdue and I cannot help but be concerned. Do any of you remember Hurricane Frederic? Thank you for allowing me to join in the blog and I look forward to hearing from y'all! :)
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Member Since: July 12, 2011 Posts: 0 Comments: 1532
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Quoting RitaEvac:
Buckle up folks, 91L is gonna start off the season with a bang


I'm afraid that you are correct.
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Link we have more tropical waves
Member Since: July 12, 2011 Posts: 0 Comments: 1532
Don formed in the face of unfavorable conditions, and that's a sign that's $%!T is gonna hit the fan starting with 91L and the rest of season
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Quoting RitaEvac:
Buckle up folks, 91L is gonna start off the season with a bang


Looks that way doesn't it.
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The circulation of 91L is tightening up, especially on the western side of the developing surface low. I put the developing coc at 9.9n/43.8w
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Buckle up folks, 91L is gonna start off the season with a bang
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All models showing hurricane for PR,Virgin Islands ,Bahamas and Florida for next weekend
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Quoting weatherman566:
91L is still too broad and needs more convection around the center before I see the NHC upgrade their percentages. Large systems take awhile to organize. Newest infrared images showing convection developing, so we'll see what happens.

actually thats not quite right i believe a T.C.F.A. is coming soon real soon
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Strong rotation

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Quoting jasonweatherman2011:
new video out!!


Was that really necessary?

Music made it sound as if we were dealing with Hurricane Hugo or something...
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Quoting TXEER:
What is the difference between the "computer models" and the "ensemble models"?




Ensemble models are the same models ran multiple times with slightly differnt initial conditions and peramiter tweaks. Or something like that...
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Gee, sorry. I mistakenly thought, a "fish", was a storm, that wouldn't interfere with anything important. Silly Me.
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Quoting PensacolaDoug:


I shoulda flown the "sarcasm flag"!
Not necessary. Common sense would tell anyone you were joking.
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Quoting stormwatcherCI:
Yes he is.


I shoulda flown the "sarcasm flag"!
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Quoting P451:
It's coming straight at me.



I'm about to get my ass kicked. For reference about half way down the wider part of the Hudson, east side of the river.

Huge bolt of lightning just rocked the neighborhood real bad.

Apparently this thing is putting out 2500 strikes in 15 minutes (at least according to a local news report, I'm wondering if that's per hour).

You step outside, your hair starts to stand out. I think I'll stay inside.




There's a tornado warned supercell headed towards my home in NJ.

Can't believe that when I go overseas I finally get a good storm up there.

Keep me updated.
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812. TXEER
What is the difference between the "computer models" and the "ensemble models"?

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Quoting xcool:


91L really looks monstrous on that loop.
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Are my eyes playing tricks on me or is Don trying to form a last minute eye?
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809. P451
It's coming straight at me.



I'm about to get my ass kicked. For reference about half way down the wider part of the Hudson, east side of the river.

Huge bolt of lightning just rocked the neighborhood real bad.

Apparently this thing is putting out 2500 strikes in 15 minutes (at least according to a local news report, I'm wondering if that's per hour).

You step outside, your hair starts to stand out. I think I'll stay inside.

Member Since: December 16, 2007 Posts: 7 Comments: 10202
POSS T.C.F.A.
XX/INV/91L
MARK
9.45N/43.75W
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04L/TS/D/Cx
FINAL DESTINATION


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91L is still too broad and needs more convection around the center before I see the NHC upgrade their percentages. Large systems take awhile to organize. Newest infrared images showing convection developing, so we'll see what happens.

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Quoting palmasdelrio:


You're joking, right?
Yes he is.
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Your ignorance offends me
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803. SLU
Quoting JLPR2:


PR alone has a population close to 4mil. :\


And finger's crossed it veers away from Haiti or else this could be the last we hear of "Emily".
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Quoting PensacolaDoug:



You mean there's people on those islands?




You're joking, right?
Member Since: May 22, 2008 Posts: 0 Comments: 182
Those to the southeast of this cell in NY need to head warnings and take cover. Storm Velocity's look good with this storm.





TORNADO WARNING
NYC071-087-119-292200-
/O.NEW.KOKX.TO.W.0003.110729T2122Z-110729T2200Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE NEW YORK NY
522 PM EDT FRI JUL 29 2011

THE NATIONAL WEATHER SERVICE IN UPTON NY HAS ISSUED A

* TORNADO WARNING FOR...
WESTCHESTER COUNTY IN SOUTHEAST NEW YORK...
ROCKLAND COUNTY IN SOUTHEAST NEW YORK...
EASTERN ORANGE COUNTY IN SOUTHEAST NEW YORK...

* UNTIL 600 PM EDT...

* AT 518 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO NEAR MONROE...
MOVING SOUTHEAST AT 30 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
HARRIMAN...WEST POINT...POMONA...PEEKSKILL...NEW CITY AND
HAVERSTRAW

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IN ADDITION TO THE TORNADO...THIS STORM IS CAPABLE OF PRODUCING 2
INCH DIAMETER SIZE HAIL AND DESTRUCTIVE STRAIGHT LINE WINDS.

WHEN A TORNADO WARNING IS ISSUED BASED ON DOPPLER RADAR...IT MEANS
THAT STRONG ROTATION HAS BEEN DETECTED IN THE STORM. A TORNADO MAY
ALREADY BE ON THE GROUND...OR IS EXPECTED TO DEVELOP SHORTLY. IF YOU
ARE IN THE PATH OF THIS DANGEROUS STORM...MOVE INDOORS AND TO THE
LOWEST LEVEL OF THE BUILDING. STAY AWAY FROM WINDOWS. IF DRIVING...DO
NOT SEEK SHELTER UNDER A HIGHWAY OVERPASS.

THE SAFEST PLACE TO BE DURING A TORNADO IS IN A BASEMENT. GET UNDER A
WORKBENCH OR OTHER PIECE OF STURDY FURNITURE. IF NO BASEMENT IS
AVAILABLE...SEEK SHELTER ON THE LOWEST FLOOR OF THE BUILDING IN AN
INTERIOR HALLWAY OR ROOM SUCH AS A CLOSET. USE BLANKETS OR PILLOWS TO
COVER YOUR BODY AND ALWAYS STAY AWAY FROM WINDOWS.

IF IN MOBILE HOMES OR VEHICLES...EVACUATE THEM AND GET INSIDE A
SUBSTANTIAL SHELTER. IF NO SHELTER IS AVAILABLE...LIE FLAT IN THE
NEAREST DITCH OR OTHER LOW SPOT AND COVER YOUR HEAD WITH YOUR HANDS.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 1100 PM FRIDAY EVENING FOR
NORTHEAST NEW JERSEY AND SOUTHEAST NEW YORK. A SEVERE THUNDERSTORM
WATCH ALSO REMAINS IN EFFECT UNTIL 1100 PM FRIDAY EVENING FOR
NORTHEAST NEW JERSEY AND SOUTHEAST NEW YORK.
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800. SLU
Quoting PensacolaDoug:



You mean there's people on those islands?




No they're all uninhabited.
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Quoting seafarer459:
Although I have been A member for a while. I rarely post these days. Having said that. ANYONE, who thinks an Island busting storm is a "fish", needs therapy. Or..if.., you are basing your entire forecast on one model ,a bit of advice. Keep your ears and eyes open, and your big mouth shut! Ignorance is curable, stupidity is permanent.





A little overboard don't ya think? Just 'cause somebody refers to a storm as a "fish" doesn't mean they don't have any empathy for the folks in the islands..And who knows..It may just miss.
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798. JLPR2
Quoting SLU:


Well almost 5 million lives are in the path of this "fish storm" in case you didn't know ....


PR alone has a population close to 4mil. :\
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wow!! the low is moving more west here by looking at this map!!
Member Since: July 12, 2011 Posts: 0 Comments: 1532
Quoting PensacolaDoug:



You mean there's people on those islands?


So, you wanna be a comedian. LOL
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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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