Don battling dry air and wind shear

By: Dr. Jeff Masters , 7:37 PM GMT en Julio 28, 2011

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Tropical Storm Don continues to be an unimpressive low-end tropical storm as it continues northwest towards the Texas coast. Don formed yesterday afternoon from an African tropical wave that moved into the Gulf of Mexico under a region of low wind shear. Don's formation date of July 27 is nearly a month ahead of the usual August 23 date for the arrival of the season's fourth named storm of the year. There is currently no hurricane hunter airplane in Don, and a new airplane is not due in the storm until tonight. The last center fix at 1pm EDT found surface winds of 45 mph and a central pressure of 1005 mb, a 4 mb rise from earlier this morning. Water vapor satellite images show a region of dry air to the northwest of Don, over the western Gulf of Mexico. Wind shear as diagnosed by the University of Wisconsin CIMSS group and the SHIPS model show a moderate 5 - 15 knots of shear from strong upper level winds out of the north. This shear is creating problems for Don by injecting dry air into the system. Visible satellite imagery from early this afternoon showed the presence of surface arc-shaped clouds expanding outwards to the north from the center of Don. These type of clouds are a sign that the storm is struggling with dry air. When dry air at middle levels of the atmosphere gets injected into thunderstorms due to wind shear, the dry air tends to create strong downdrafts that rob the storm of moisture. These downdrafts spread out at the ocean surface and create arc-shaped surface cumulus clouds.


Figure 1. Visible satellite image of Don from pm EDT July 28, 2011, showing arc-shaped surface clouds--the tell-tale sign of dry air interfering with the storm's organization.


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 big question for Don is, will it bring significant rains to Texas? According to the National Climatic Data Center, the six-month period ending in June 2011 was the driest on record. Average rain between January and June was more than eight inches (203 millimeters) below average in Texas, and the state experienced record heat between April and June. The heat and lack of rain have brought exceptional drought--the highest category of drought--to over 75% of the state. Don has the potential to bring some decent drought-busting rains to the state. If Don can expand in size and intensify to a 50 - 55 mph tropical storm, it has the capability to bring hundreds of millions of dollars worth of beneficial rains to the state. We don't want Don to stay in its current state, which is too small and weak to bring significant rains to Texas. If Don follows the current NHC forecast, which brings the storm up to a moderate-strength tropical storm, that would be just right. Don's small size makes it prone to dry air and wind shear, though, and it is uncertain whether the storm can overcome these problems enough to become a significant rain maker. NHC gave Don a 12% chance of intensifying into a hurricane in the 11am advisory, which is a reasonable forecast, since Don is running out of time to get its act together in time to become a hurricane. None of the computer models is predicting Don will become a hurricane.

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 Port O'Connor, Texas has the highest chance of tropical storm-force winds (39+ mph): 45%.

New hurricane archive search feature
The autocomplete entities in the wunderground search box has been extended to include hurricanes, so you can now search for a storm by name, year, or basin. Here are some examples in case you feel like exploring your new options:

By name:

Hurricane David - Atlantic, 1979
David, Major Hurricane - Atlantic, 1979
Major Hurricane David - Atlantic, 1979

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2005 Hurricanes Atlantic
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By basin:

Hurricanes Western Pacific 2011
Hurricanes Atlantic 2008

By category:

Tropical Storms Atlantic 2005
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Extratropical Storms Western Pacific 1988

I'll have a new post Friday morning.

Jeff Masters

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Quoting Stormchaser2007:
Red square is the center.



Excuse my French, but damn.
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If 91L does develop and move through the Caribbean, it will probably try to move up to around the Yucatan. However, unless the pattern that has been in place across the United States for the whole summer finally changes, I think the US from Louisiana and east of there would be safe because of the giant death ridge. There might would be an opportunity for Central/South TX to receive the brunt. Obviously, that's just pure speculation at this point and something to keep in the back of your mind. If it tracks north of the islands, it will obviously be susceptible to any trof moving off the Eastern Seaboard. However, if there is no trof, it could be steered into FL. We'll see. Just some brainstorming that I'm doing out loud.
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Red square is the center.

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I'm not part of the night shift? =(, OUCH.
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Quoting Stormchaser2007:
NOT a good track...

FULL IMAGE



Well, the reliable models kept it north on their first runs. I guess the HWRF took it through the Caribbean, though. *Gulp* Good thing we have plenty of time to watch.
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Quoting bigwes6844:
and you too
Lol, I was gonna post the same thing.
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Quoting bigwes6844:
and you too


Aw, shucks. LOL. Thanks, Wes. I do what I can!
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NOT a good track...

FULL IMAGE

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Quoting MississippiWx:


Yep. The night shift is the best, especially when we actually have good bloggers like yourself, JRRP and StormChaser on!
and you too
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So the the potential for a Caribbean cruiser all the way to a fish exists right now with an environment conductive for RI. Fun times ahead.
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Donnie still blowing up convection in the middle...not dying off this time:

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Quoting MiamiHurricanes09:
Would be nice if the blog was this calm during the afternoon...lol.


Yep. The night shift is the best, especially when we actually have good bloggers like yourself, JRRP and StormChaser on!
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Quoting MiamiHurricanes09:
Would be nice if the blog was this calm during the afternoon...lol.


Night shift is always the best.

Been that way since the blog started.
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Check out Donnie boy with outflow on all sides for once:

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Would be nice if the blog was this calm during the afternoon...lol.
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1954. Ryuujin
Quoting Stormchaser2007:
Watch out PR

114 hours


Oh damn and unless I'm reading the high incorrectly, it looks like the steering for that thing is right into FL.
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1953. JRRP
Quoting Ryuujin:


Yeesh

Lets hope that this is one time where the models get a little over-eager. I'd hate to see a monster spiraling up towards the East Coast of Florida / SE US.

well....



bed time...


by the way
91L east of Nicaragua

Euro
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Quoting Ryuujin:


What is going on with the models? They're acting like 16 year olds that just found their parents alcohol locker.
When you have extremely favorable conditions you get models that forecast invests to turn into major hurricanes in a matter of days.

If the conditions that the SHIPS displays were to verify, I don't see why it couldn't happen to be honest.
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Watch out PR

114 hours

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Intensity consensus model has a MH

AL, 91, 2011072906, 03, IVCN, 0, 0N, 0W, 25, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 12, 0N, 0W, 33, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 24, 0N, 0W, 42, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 36, 0N, 0W, 53, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 48, 0N, 0W, 65, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 60, 0N, 0W, 79, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 72, 0N, 0W, 93, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 84, 0N, 0W, 105, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 96, 0N, 0W, 109, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 108, 0N, 0W, 111, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, IVCN, 120, 0N, 0W, 110, 0, , 0, , 0, 0, 0, 0,
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Quoting Stormchaser2007:
Oh boy...

Quoting MiamiHurricanes09:
SHIPS basically depicts a doom scenario, upper-level winds of less than 3 knots after 24 hours, a moist mid-level environment, and a warm ocean surface with plenty of heat content:

Darn, Stormchaser beat me to it, lol.


Good Lord...The islands are screwed if that comes to pass...
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1948. Ryuujin
Quoting MiamiHurricanes09:
Even this is impressive:

Prob of RI for 25 kt RI threshold= 44% is 3.4 times the sample mean(12.8%)


What is going on with the models? They're acting like 16 year olds that just found their parents alcohol locker.
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Quoting Ryuujin:


Yeesh

Lets hope that this is one time where the models get a little over-eager. I'd hate to see a monster spiraling up towards the East Coast of Florida / SE US.


I wouldn't, dude, I live to see stuff like that, man.
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Even this is impressive:

Prob of RI for 25 kt RI threshold= 44% is 3.4 times the sample mean(12.8%)
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Practically no shear and good-great ML moisture.

Emily 2005 redux?
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wow, that wind speed is extremely unlikely, but compelling, nevertheless.
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1943. Ryuujin
Quoting JRRP:
3
123mph ?????
WTF


Yeesh

Lets hope that this is one time where the models get a little over-eager. I'd hate to see a monster spiraling up towards the East Coast of Florida / SE US.
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SHIPS basically depicts a doom scenario, upper-level winds of less than 3 knots after 24 hours, a moist mid-level environment, and a warm ocean surface with plenty of heat content:

Darn, Stormchaser beat me to it, lol.
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Seeing a 5-1-1 into the 1st week of Aug...
Member Since: Agosto 30, 2008 Posts: 1 Comments: 259
Oh boy...

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Ayyy Dios mio, em meoooooooo, LOL, wow.
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Quoting Stormchaser2007:
LOL!

The LGEM,SHIPS, and DSHIPS take 91L over 100knots!

LGEM


AL, 91, 2011072906, 03, LGEM, 0, 85N, 410W, 25, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 12, 91N, 429W, 31, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 24, 100N, 448W, 40, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 36, 111N, 471W, 50, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 48, 121N, 498W, 62, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 60, 129N, 526W, 78, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 72, 133N, 552W, 97, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 84, 137N, 579W, 111, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 96, 141N, 604W, 117, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 108, 150N, 627W, 116, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 120, 161N, 647W, 112, 0, , 0, , 0, 0, 0, 0,


Yikes. Those tracks take it south of the big islands as well.
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1937. JRRP
3
123mph ?????
WTF
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SHIPS

AL, 91, 2011072906, 03, SHIP, 0, 85N, 410W, 25, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 12, 91N, 429W, 34, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 24, 100N, 448W, 44, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 36, 111N, 471W, 55, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 48, 121N, 498W, 67, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 60, 129N, 526W, 80, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 72, 133N, 552W, 88, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 84, 137N, 579W, 98, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 96, 141N, 604W, 101, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 108, 150N, 627W, 105, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, SHIP, 120, 161N, 647W, 107, 0, , 0, , 0, 0, 0, 0,
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All intensity models take it above 105 knots. Wow...lol.
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LOL!

The LGEM,SHIPS, and DSHIPS take 91L over 100knots!

LGEM


AL, 91, 2011072906, 03, LGEM, 0, 85N, 410W, 25, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 12, 91N, 429W, 31, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 24, 100N, 448W, 40, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 36, 111N, 471W, 50, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 48, 121N, 498W, 62, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 60, 129N, 526W, 78, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 72, 133N, 552W, 97, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 84, 137N, 579W, 111, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 96, 141N, 604W, 117, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 108, 150N, 627W, 116, 0, , 0, , 0, 0, 0, 0,
AL, 91, 2011072906, 03, LGEM, 120, 161N, 647W, 112, 0, , 0, , 0, 0, 0, 0,
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Winds 5kts higher, pressure the same:

AL, 91, 2011072906, , BEST, 0, 85N, 410W, 25, 1008, LO,
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Quoting Ryuujin:


It's not? I thought his center was under that? Is it still to the north of the convection a bit?


It's underneath the convection, just not in the exact center of it.
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Quoting Stormchaser2007:
Imagine if the center was under that deep convection...


It will probably slowly slide more to the center of that convection if it persists. Looks good right now.
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1930. Ryuujin
Quoting Stormchaser2007:
Imagine if the center was under that deep convection...


It's not? I thought his center was under that? Is it still to the north of the convection a bit?
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Quoting JRRP:
.
si pero no muestra circulacion cerrada...


Lo se, pero a pesar de eso y sin embargo, sigue ahi.
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Don looks the best yet and he's actually sustaining convection:

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6z BAM suite shifted south.
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Imagine if the center was under that deep convection...
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wow!! look what is happern here!!
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1924. JRRP
Quoting Floridian2011:



Como que nada, chico? Mirala ahi? Andas medio ciego, o que? LOL.
.
si pero no muestra circulacion cerrada...
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Quoting FrankZapper:
Impersonation?


Yeah, it's not actually him. If you've been on the blog as long as me, you can actually tell when it's the real one. Anyway, it doesn't matter. The fake one is on ignore now.
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1922. JRRP

new
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Quoting MississippiWx:


Since the blog has slowed down now, I'll say this...

Your JFV impersonation is really bad. It's also pretty pathetic that you'd want to impersonate a troll.
Impersonation?
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About

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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