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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196. Gorty
Quoting jasonweatherman2011:
New England is save from a hurricane!! the jetstream its there!!


but it can change down the road.
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195. Gorty
Quoting tiggeriffic:


anything and everything is a chance...you will have to wait till it gets closer to PR to see that tho... give it till tue or wed


Ok thanks!
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Difference from last year P451, IMO, is that the anticipated pattern change that never came last year was to that of High Pressure on the east coast. High pressure is already well established this year so the pattern change would be to that of low pressure or troughiness on the East Coast.
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Quoting Waltanater:
I just love the DOOMCASTING. Keep it up.


Member Since: July 15, 2006 Posts: 171 Comments: 53827
Quoting tiggeriffic:


same thing...idk...maybe i should show it my DD214 from being in the Navy, maybe that would work lol


LOL..I'm sure that would!!
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Quoting Gorty:
Any chance invest 91 which could become Emily come up to me in New England?


anything and everything is a chance...you will have to wait till it gets closer to PR to see that tho... give it till tue or wed
Member Since: September 16, 2007 Posts: 0 Comments: 3650
Quoting P451:


Really intense storms are sometimes able to produce their own upper level atmospheric conditions and impose their will on the surrounding conditions. It's a fairly rare occurrence however.

At this time I wouldn't look much if at all towards any model runs - especially those for steering.

Personally I don't think the Atlantic high is so intense that I'd be predicting an East Coast landfall - or brush - with a potential system developing from 91L.

We went through that time and again last season - expecting a pattern change - hearing about someone humping the ridge - it's going due west look at the ridge - etc. Only to see...



...occur. If those who put so much into the 2010 Atlantic High had their opinion pan out then everything was going to slam into the SE US coastline.

So, let's not make the same mistake.

That should serve as a learning experience more than ever.


LOL..I dont think anyone will be quoting a pattern change or pumping the ridge scenario but yeah I see your point..
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I just love the DOOMCASTING. Keep it up.
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187. Gorty
Any chance invest 91 which could become Emily come up to me in New England?
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Quoting ncstorm:


850 mb Vorticity run was what I was posting..the navy is so funny with links and all..you cant post the images, at least I cant and sometimes the links dont work when I do post them....here is the link below

https://www.fnmoc.navy.mil/wxmap_cgi/cgi-bin/wxma p_loop.cgi?&area=ngp_troplant&prod=z85& ;dtg=2011072 912&set=Tropical


same thing...idk...maybe i should show it my DD214 from being in the Navy, maybe that would work lol
Member Since: September 16, 2007 Posts: 0 Comments: 3650
Quoting NotCircumventing:
12Z GFS shows a recurving system... between East Coast and Bermuda.

Yawn.


GFS has a known cold bias. So it always amplifies Trofs versus ridges. It showed up repeatedly last year. It would recurve the storms like Ivan and Earl and Danielle way way out into the ocean well before they actually turned. Now it's barely recurving 91L off the coast, which in my mind means it's hinting to a greater risk of US landfall. We won't know anything, however, until 91L actually forms into a storm and we get a true center fix on it. So no point in speculating where it may or may not go at the moment.
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Quoting tiggeriffic:


keep getting error...cant open :( but thought i saw it earlier and showed the high flatten out over bermuda...is that the map you were linking to?


850 mb Vorticity run was what I was posting..the navy is so funny with links and all..you cant post the images, at least I cant and sometimes the links dont work when I do post them....here is the link below

https://www.fnmoc.navy.mil/wxmap_cgi/cgi-bin/wxma p_loop.cgi?&area=ngp_troplant&prod=z85&dtg=2011072 912&set=Tropical
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Quoting ncstorm:


12Z NOGAPS is seeing a more southern route..up to 120 hours so far

Link


keep getting error...cant open :( but thought i saw it earlier and showed the high flatten out over bermuda...is that the map you were linking to?
Member Since: September 16, 2007 Posts: 0 Comments: 3650
Quoting jasonweatherman2011:
i bet you the modeles will move little more to the south at 2pm


12Z NOGAPS is seeing a more southern route..up to 120 hours so far

Link
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Quoting CorneliaMarie:
Gnome man! You changed your avatar!!!!!!


:)
Member Since: August 22, 2008 Posts: 12 Comments: 6010
176. JRRP
Quoting nigel20:
If you look at some of the model runs for hurricane dean, they had it clipping the NE carib, but it went further south.


that is true
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Quoting angiest:


GFS thinks this is 2010.


exactly...the highs are not sticking like they are pose to...this one is gonna flatten out...
Member Since: September 16, 2007 Posts: 0 Comments: 3650
If you look at some of the model runs for hurricane dean, they had it clipping the NE carib, but it went further south.
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172. srada
Quoting NotCircumventing:
12Z GFS shows a recurving system... between East Coast and Bermuda.

Yawn.


oh how many times have we seen a model predicting recurve and it dosent?..
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Quoting jasonweatherman2011:
very bad!!


Give it a couple days might be it gets stronger
But I thinks its alittle North in that run anyway IMO
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Quoting NotCircumventing:
12Z GFS shows a recurving system... between East Coast and Bermuda.

Yawn.


GFS thinks this is 2010.
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Quoting angiest:


Early this morning it said 120-125mph. Much salt needed yet.


wow. thanks

keep an eye on that one!
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Quoting PurpleDrank:
so the SHIPS model predicts 91L a 85mph hurricane in 120 hours?


Early this morning it said 120-125mph. Much salt needed yet.
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Quoting NotCircumventing:
12Z GFS shows a recurving system... between East Coast and Bermuda.

Yawn.


that is if the high doesn't flatten out...still a good chance for that happening b4 it could recurve...
Member Since: September 16, 2007 Posts: 0 Comments: 3650
so the SHIPS model predicts 91L a 85mph hurricane in 120 hours?
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Quoting 7544:
llc forming on 91l ?


OSCAT last night showed a surface circulation with 91L

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Quoting NotCircumventing:
12Z GFS 174



shows some consistency with 6Z


I see that (pre) Emily is moving WNW (24N 71W) -> (25N 74W)
Member Since: August 30, 2008 Posts: 1 Comments: 259
159. 7544
llc forming on 91l ?
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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?


Based on the tracks right now, it looks okay. But as you stated it's a ways out yet. And the models are guaranteed to change. Take a look at Levi's blog for a good read on his thoughts on 91L.
Member Since: August 22, 2008 Posts: 12 Comments: 6010
Quoting tiggeriffic:


salmon and spicy tuna are my favs...tell your "REAL MEN" buds that when you don't catch a fish you ALWAYS eat the bait roflmbo


Lol....I have Bud in Miami (Fishing Guide) who brings the soy and wasabi on the boat and cuts up any Dolphin (Mahi Mahi) on the spot for lunch.........
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agreed
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Quoting NotCircumventing:
actually 12Z going stronger than 6Z


a stronger storm would make its own steering..at least thats what I heard..lets hope it dosent keep going up with each run..
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really what it boils down to is how strong or weak the high or trough is for 91L

seems like a large enough circulation. if it can get by the dry air and upper level winds, this could be a big one
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and in reality the 12Z GFS does not show that strong of a system maybe similar to what we have now with Don...you can clearly see the trough over the NW Atlantic on that run but with a shallow system like it shows i'm not totally sure that trough will be strong enough to lift the storm out to sea...it may turn back west...the reason the models are going such North of the Islands is because they develop this storm very quickly and swiftly...we will have to see if that comes to pass if its stay weaker the trough might not have that much of an affect at all
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Quoting tiggeriffic:


ships are the first to be warned and get out of the area if there is eminant danger in weather...worst case is you see a different area or they refund your money...it is a gamble either way, it is about 5 days from PR as of today...sunday would be 3 days away...call the cruise company and ask their policy is your best bet at this point today


Thanks for the advice... however, we are flying down and staying in a condo. So we are either all in or all out. No ship taking a different course here.
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Quoting tiggeriffic:


ships are the first to be warned and get out of the area if there is eminant danger in weather...worst case is you see a different area or they refund your money...it is a gamble either way, it is about 5 days from PR as of today...sunday would be 3 days away...call the cruise company and ask their policy is your best bet at this point today


Most vacation packages should have a hurricane policy attach to them..always when booking your vacation ask about it because you may find out the hard way if they dont have one and you are out of a vacation and money should a hurricane heads towards your designated area..
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Quoting weathermanwannabe:


Wife and kids going to Atlanta for the weekend and I do not cook (except for blackend or broiled filets); Love shushimi and headed in the same direction this weekend if I don't catch any fish myself.....My real men fishing buds won't eat "bait"........... :)


salmon and spicy tuna are my favs...tell your "REAL MEN" buds that when you don't catch a fish you ALWAYS eat the bait roflmbo
Member Since: September 16, 2007 Posts: 0 Comments: 3650
148. 7544
Quoting WoodyFL:


now that get a WOW WOW LOOKS LIOKE IT GOING TO BE VERY CLOSE to the bahamas tho then who knows the high has been moving strange this year
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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.