Don battling dry air and wind shear

By: Dr. Jeff Masters , 7:37 PM GMT on July 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

By year:

2005 Hurricanes Atlantic
2007 Hurricanes Eastern Pacific

By basin:

Hurricanes Western Pacific 2011
Hurricanes Atlantic 2008

By category:

Tropical Storms Atlantic 2005
Tropical Depressions Indian Ocean 2011
Subtropical Storms Eastern Pacific 2010
Extratropical Storms Western Pacific 1988

I'll have a new post Friday morning.

Jeff Masters

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Quoting Floridian2011:


Hi there, NONE of those criterias are needed in order for it to be designated as an invest, now, a TD designation on the other hand, that's an entirely different other story.

Courtesy: The NHC website, =).


The KID really just repeated what has been said about pre 91L and yes there really is NO criteria for an Invest other than someone at NHC yelling we have an INvest. What he said in the 3 bullets are comments that have been said about the current condition of pre 91L and he was correct about those conditions.
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Quoting stormpetrol:
I think Ivan 04(cold Chills) became a hurricane below 10N , a closed low ,warm core, reasonable convection, and 30mph = a TD


A hurricane? If I'm not mistaken, he became a major hurricane.
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Quoting JLPR2:


I'm two miles inland. Yikes! XD


Oh geez, I always assumed you were farther inland for some reason. Then again, in your case, perhaps it's better that you are close to the coast, because Puerto Rico has inland mountains, which would enhance the wind effect of a landfalling hurricane.
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1518. IMA
Watched a lot of cotton comin' in last weekend just outside of Corpus. The only fields that weren't withered & not worth harvesting were the irrigated ones on larger places.
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Don only has a small window in the am to attain Hu Status, I think I might have to eat that filthy bird! :)
Member Since: April 29, 2007 Posts: 0 Comments: 8024
Quoting CanesfanatUT:


Agreed - has to go through the graveyard of the Western Carib.


The western Caribbean? I think you mean the eastern Caribbean.
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Quoting angiest:


I live about the same distance inland. My evacuation requirements are a Cat 3 or higher hitting between roughly Bay City and the Bolivar Peninsula.

The builders made a mistake when they put my roof on, and I don't want to be here to find out if the fix worked correctly (the purlin struts were installed at too shallow an angle. A second set was installed), and not living on the coast, no hurricane straps. Plus, kids don't like storms, and the little one (who has cystic fibrosis) doesn't need to be without power and A/C. So, it makes sense to give them a trip to the grandparents.


Ah, yes. Storms are always much more difficult when kids are involved. I have a two week old brother that would have extreme difficulty in coping with the inevitable heat that would bake us after the storm passed.
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Quoting stormpetrol:
I think Ivan 04(cold Chills) became a hurricane below 10N , a closed low ,warm core, reasonable convection, and 30mph = a TD


you forgot one - persistence

If it lacks that, the rest of it does not mean much
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1513. GHOSTY1
Quoting doabarrelroll:


You can see why people would be sensitive. Imagine if Ike was a Cat 3 4 or 5


Alright, for your information Ike had some qualities that were more than cat 2 such as the surge that was up to Cat 3 or 4 levels that destroyed thousands of lives, so don't act like i don't understand about what i'm talking about.
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1512. KEEPEROFTHEGATE (Mod)
04L/TS/D/Cx



weakening flag ON
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1511. angiest
Quoting GHOSTY1:


Your right i may have gotten a little to aggresive with our need for help i hope for the best for everyone. I had a question though, My family and i go to Rockport alot and we drive by cotton fields on the way there but they seem to be down in numbers to, is it just the farms we go by? I hope you have good luck in your future and you have a good harvest.


We take TX 60 from Wallis to Bay City to pick up 35. All the corn was dead, the cotton didn't look great. The Sorghum was. But that was a month ago.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1509. IMA
Quoting angiest:


Was this official there for Alex's rains last year? Houston got a fair amount of flooding from him.
Shoot I'd love to show him some info on Allison!
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1508. j2008
Quoting TampaSpin:
Pre 91L is far from becoming a TD. Maybe by Sunday or MOnday we might be 48hrs from a TD. It is turning lots of atmosphere and will take time to get a good spin a going! Again the models are not supporting much development!

Models havn't been very good though this year. I wouldnt trust them to much.
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I think Ivan 04(cold Chills) became a hurricane below 10N , a closed low ,warm core, reasonable convection, and 30mph = a TD
Member Since: April 29, 2007 Posts: 0 Comments: 8024
1506. KEEPEROFTHEGATE (Mod)
XX/AOI/XXL
MARK
10.45N/41.75W
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Quoting KoritheMan:


Best case scenario (in terms of recurvature probabilities) would be for pre 91L to strengthen significantly, as it would increase the likelihood of it feeling a profound weakness within the subtropical ridge.

Don't see that happening, though; rapid development, I mean -- though recurvature may still be a possibility depending on the evolution of the synoptic scale pattern.


Agreed - has to go through the graveyard of the Western Carib.
Member Since: September 3, 2007 Posts: 0 Comments: 527
1503. MTWX
Quoting IMA:
San Antonio city official, speaking from the EOM, "It might be a tropical storm but it could be a category hurricane". That's not a typo, he said "category hurricane". He also said it as if a "category" hurricane would be more of a problem (for San Antonio)than a TS in regards to flooding. Amazing that we don't have a better-informed city official to speak on behalf of the EOM, especially considering how many times we've had significant flooding from a TS here & almost never any real wind damage, other than from tornadic activity (or coastal evacuees) from a hurricane. lol


I can see how the way the Interstates go through there can be both a blessing and a curse. Great for managing traffic, but not so good on the lower level for flooding.
Member Since: July 20, 2009 Posts: 23 Comments: 1393
1502. JLPR2
Quoting KoritheMan:


Eh, it's kind of a mixed bag. I've been through 100 mph winds, yet I have refused to evacuate in the event of another one (unless it's exceptionally severe). My family says they are, but I will stay behind and capture the footage on film.

Then again, I am 70 miles inland, so the storms I do get typically weaken quite markedly by the time they make it this way.


I'm two miles inland. Yikes! XD
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting doabarrelroll:

A closed tight broad huh. cool.
too bad she's closed
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Goodnight to Don Quixote
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Quoting TampaSpin:
Pre 91L is far from becoming a TD. Maybe by Sunday or MOnday we might be 48hrs from a TD. It is turning lots of atmosphere and will take time to get a good spin a going! Again the models are not supporting much development!


Screw the models, they've performed horrible this season.
Member Since: July 6, 2010 Posts: 113 Comments: 32530
1498. GHOSTY1
Quoting 422brzyldy:



I get your point. However, the cotton farmers are just a few weeks away from harvesting. Too much of a good thing (ie - rain) would be detrimental for them. Let's hold off a couple more weeks before we pray we get too much.... I'm a rancher, born and bred, but I can buy hay (albeit at a higher price right now)- the grass is already dead as is everything else we've planted. Let's pray the cotton growers get theirs in before the Lord gives us a break.


Your right i may have gotten a little to aggresive with our need for help i hope for the best for everyone. I had a question though, My family and i go to Rockport alot and we drive by cotton fields on the way there but they seem to be down in numbers to, is it just the farms we go by? I hope you have good luck in your future and you have a good harvest.
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1496. angiest
Quoting IMA:
San Antonio city official, speaking from the EOM, "It might be a tropical storm but it could be a category hurricane". That's not a typo, he said "category hurricane". He also said it as if a "category" hurricane would be more of a problem (for San Antonio)than a TS in regards to flooding. Amazing that we don't have a better-informed city official to speak on behalf of the EOM, especially considering how many times we've had significant flooding from a TS here & almost never any real wind damage, other than from tornadic activity (or coastal evacuees) from a hurricane. lol


Was this official there for Alex's rains last year? Houston got a fair amount of flooding from him.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Pre 91L is far from becoming a TD. Maybe by Sunday or MOnday we might be 48hrs from a TD. It is turning lots of atmosphere and will take time to get a good spin a going! Again the models are not supporting much development!
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Quoting Hurricanes101:


Designation of an invest does not need any of these things



I should reword that. I was talking about for TD/TS designation.
Member Since: July 6, 2010 Posts: 113 Comments: 32530
1493. angiest
Quoting KoritheMan:


Eh, it's kind of a mixed bag. I've been through 100 mph winds, yet I have refused to evacuate in the event of another one (unless it's exceptionally severe). My family says they are, but I will stay behind and capture the footage on film.

Then again, I am 70 miles inland, so the storms I do get typically weaken quite markedly by the time they make it this way.


I live about the same distance inland. My evacuation requirements are a Cat 3 or higher hitting between roughly Bay City and the Bolivar Peninsula.

The builders made a mistake when they put my roof on, and I don't want to be here to find out if the fix worked correctly (the purlin struts were installed at too shallow an angle. A second set was installed), and not living on the coast, no hurricane straps. Plus, kids don't like storms, and the little one (who has cystic fibrosis) doesn't need to be without power and A/C. So, it makes sense to give them a trip to the grandparents.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting IMA:
San Antonio city official, speaking from the EOM, "It might be a tropical storm but it could be a category hurricane". That's not a typo, he said "category hurricane". He also said it as if a "category" hurricane would be more of a problem (for San Antonio)than a TS in regards to flooding. Amazing that we don't have a better-informed city official to speak on behalf of the EOM, especially considering how many times we've had significant flooding from a TS here & almost never any real wind damage, other than from tornadic activity (or coastal evacuees) from a hurricane. lol


How amusing. Sad, but amusing.
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1491. ackee
Quoting MississippiWx:


The key word that the original post says is "hints".
thanks that why used the word hint when u compare the ECMWF to other models so far this seasons its has been out performing the other models by far
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1490. Ossqss
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Quoting TropicalAnalystwx13:
The problem with pre-91L right now is three things:

1.) It is still embedded within the ITCZ. No designation until it separates.

2.) It lacks a lot of organized deep convection. Until then, probably not a designation.

3.) It probably lacks the wind speeds needed, so no designation until then.

It may be able to fix all these by Monday, but it will be a close call.


Designation of an invest does not need any of these things

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Quoting MississippiWx:


Lol...That's funny, but messed up.


I couldn't help it :P, sorry if I offended though.
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Quoting MississippiWx:


The key word that the original post says is "hints".


Ah, yes. My bad. :P
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Quoting TropicalAnalystwx13:
The problem with pre-91L right now is three things:

1.) It is still embedded within the ITCZ. No designation until it separates.

2.) It lacks a lot of organized deep convection. Until then, probably not a designation.

3.) It probably lacks the wind speeds needed, so no designation until then.

It may be able to fix all these by Monday, but it will be a close call.


Best case scenario (in terms of recurvature probabilities) would be for pre 91L to strengthen significantly, as it would increase the likelihood of it feeling a profound weakness within the subtropical ridge.

Don't see that happening, though; rapid development, I mean -- though recurvature may still be a possibility depending on the evolution of the synoptic scale pattern.
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Quoting ElConando:


Yes?


Ha! Was waiting for that.
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1483. IMA
San Antonio city official, speaking from the EOM, "It might be a tropical storm but it could be a category hurricane". That's not a typo, he said "category hurricane". He also said it as if a "category" hurricane would be more of a problem (for San Antonio)than a TS in regards to flooding. Amazing that we don't have a better-informed city official to speak on behalf of the EOM, especially considering how many times we've had significant flooding from a TS here & almost never any real wind damage, other than from tornadic activity (or coastal evacuees) from a hurricane. lol
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Quoting doabarrelroll:

A closed tight broad huh. cool.


LOL. That just doesn't make any sense, on a couple of different levels.
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1480. GHOSTY1
Quoting doabarrelroll:

A closed tight broad huh. cool.


So you gonna get mad at me for asking for multiple storms to hit Texas and you make dirty jokes up? Your maturity value is minimal. Think before you speak.
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Quoting GHOSTY1:


Im sorry i said it incorrectly i didn't mean in windspeed and strength i mean i would want a large system that would be able to aleviate our drought, sorry for the misunderstanding. I live in Houston and remember Ike i was without power for 3 weeks and was lucky all the trees didn't fall on my house or the neighbors. I know many were horribly ruined by the hurricane such as Bolivar Peninsula, Galveston, etc. i know the consequences that Ike brought and i wouldn't welcome anything like that here. Sorry for miscommunication.


No problem. It's hard to read people's intent sometimes on the internet. :)
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Quoting doabarrelroll:

A closed tight broad huh. cool.

LMAO!!!!
Member Since: April 29, 2007 Posts: 0 Comments: 8024
1477. j2008
Quoting SPadreguy:
Since the GFS model run at 8 pm shows Don coming pretty much right over my house, and I live right on the Laguna Madre,I'm glad y'all assure me it won't amount to much. I'm not going to bother with my storm shutters, that is such a pain.I hope everyone is right and it's just some rain for me.

Cheak in the morning and see how strong Don is, then make your decisions. One thing I've learned is that these storms can change quick.
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Quoting KoritheMan:


The ECMWF isn't actually developing the CATL wave. When I looked earlier, it was only indicating one closed isobar, which isn't at all equivalent to a full-fledged tropical cyclone.


The key word that the original post says is "hints".
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The problem with pre-91L right now is three things:

1.) It is still embedded within the ITCZ. No designation until it separates.

2.) It lacks a lot of organized deep convection. Until then, probably not a designation.

3.) It probably lacks the wind speeds needed, so no designation until then.

It may be able to fix all these by Monday, but it will be a close call. Until it does, we won't have a TD/TS out of this.
Member Since: July 6, 2010 Posts: 113 Comments: 32530
Quoting GHOSTY1:


I dont think you understand the seriousness of the situation here in Texas, since we haven't had the rain in texas our crops are destroyed and ranchers lives are being severely impacted, were losing millions, tens of millions, and im pretty sure more than that because of the drought. What is the problem anyway with asking for good luck and plentiful rain but no since you think im just weird for some reason just forget the Texans, Go Ahead Ignore me its not like im gonna change my mind.



I get your point. However, the cotton farmers are just a few weeks away from harvesting. Too much of a good thing (ie - rain) would be detrimental for them. Let's hold off a couple more weeks before we pray we get too much.... I'm a rancher, born and bred, but I can buy hay (albeit at a higher price right now)- the grass is already dead as is everything else we've planted. Let's pray the cotton growers get theirs in before the Lord gives us a break.
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Quoting angiest:


Ike covered a large area, and therefore dropped rain over a large area. I don't remember the amounts, but since Ike came in and left it probably wasn't too bad.

Tropical systems are the only reasonable chance of making a dent in the drought in the near to medium term. It's just kinda dicey. Need the rain, not the wind and surge. And we don't need too much rain falling on the very dry ground too quickly or it all runs off.


I agree about the moisture part. But it is bad form to cite a storm which left tens-to-hundreds of thousands without power for anywhere from 1-3 weeks and access to Galveston Island cut off for over a week afterwards. Many lost their homes and have yet to recover.
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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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