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 jasonweatherman2011:
wow!! more tropical waves!!
Jason the one behind that one. Look at how HUGE that thing is.
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Quoting MississippiWx:
Nice banding is setting up with 91L:



That S shape, points to organization...
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1818. HadesGodWyvern (Mod)


1771. MTWX 4:54 AM GMT on July 29, 2011
Looks strangly of Emily '05... weird


indeed, I was thinking that as well from the models before the National Hurricane Center designated the name Don to the system.
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Quoting CybrTeddy:
If 91L develops before Monday to Emily, that would give us our 4th storm of the month of July. The most active pre-August activity since 2005. Figures we'd be using the same naming list.
if Don doesn't become a Hurricane, then it's this one for sure!
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Nice banding is setting up with 91L:

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1815. sky1989
Well, I am out too everyone. I hope everybody has a good night. It will be interesting to see what Don and 91L look like in the morning.
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1814. KEEPEROFTHEGATE (Mod)
Quoting extreme236:
No surprise that activity is picking up as we head towards August. It's gonna be a busy month.
to say the least and going in with 5 down if 91 forms which i beleive it will in the next 24 and then another 5 or 6 in august and 6 or more in sept a couple in oct maybe one in nov we could easily reach a 20 name storm season here this could be the makings of one strong season
Member Since: July 15, 2006 Posts: 168 Comments: 53285
1813. owntime
Did Don finally crap out? I just got here after a long rest.
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I get upset when the ECM starts predicting a monster like it did last year with Igor 6 days out.Dr Maue(sp?) of FSU last year said it has 1000 times the brute power of the GFS.
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If 91L develops before Monday to Emily, that would give us our 4th storm of the month of July. The most active pre-August activity since 2005. Figures we'd be using the same naming list.
Member Since: July 8, 2005 Posts: 259 Comments: 23505
Quoting KEEPEROFTHEGATE:
that track could be what i call a monster track fer sure


Yep.
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I've got to head off to bed too. Have a good night everyone!
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No surprise that activity is picking up as we head towards August. It's gonna be a busy month.
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Quoting KEEPEROFTHEGATE:
that track could be what i call a monster track fer sure


A Caribbean tracker, like Dean from 2007 and Emily from 2005 to name recent examples of Caribbean trackers. Lets hope its no where near as strong.
Member Since: July 8, 2005 Posts: 259 Comments: 23505
1806. MTWX
Got to call it a night too. See y'all in the mornin!
Member Since: July 20, 2009 Posts: 23 Comments: 1392
Quoting Floridian2011:


Espero que me comiennzes a vigilar la situacion alla bajo muyd e cera, ahora que ya se formo, amigo, =(


Mira Floridian, Se prendio el fogon, vamo a cocinar...
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Well I'm out for the night I will be back in the AM

Yall have fun :o)

Taco :o)
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1802. KEEPEROFTHEGATE (Mod)
Quoting Stormchaser2007:
Dark red line is the consensus...



that track could be what i call a monster track fer sure
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Africa is offering us 3 new sizes... in a row... And they look well defined already... Specially the 2nd one with that S shape



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Quoting MTWX:

Ike was. The other two formed up just SE of Florida.


Ok. Thanks. :) Another note about Texas landfalls Only one storm has ever crossed Florida and made landfall in Texas. That surprised me actually. Lol. I think I've just exhausted my data base of tropical knowledge. :)
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Quoting sky1989:


On the other end of the spectrum, I remember the GFS ultimately bringing the invest storm that would become Hurricane Bill into a Texas landfall in 2009.

While the models may not be good on predicting track in the long range, they are definately sometimes good at indicating favorable conditions for development.


I don't think you can take any model run past 120-144 hours too seriously, especially when its still an invest. I would agree with your above statement.
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1797. Patrap
Quoting taco2me61:


Hey Pat we have another one for you to post on now too....

Not just Don but 91L will need to be watched for sure....

Also did you get any of thr rain yesterday???? We got another 2 1/2 inches


Taco:o)


Got .98 inch Uptown
Member Since: July 3, 2005 Posts: 419 Comments: 127377
1796. MTWX
Quoting GHOSTY1:


Thats ironic Major Hurricane Emily and possible Emily nearly at the same spot, what weakened the first Emily?


Cancun
Member Since: July 20, 2009 Posts: 23 Comments: 1392
Quoting Patrap:


Hey Pat we have another one for you to post on now too....

Not just Don but 91L will need to be watched for sure....

Also did you get any of thr rain yesterday???? We got another 2 1/2 inches


Taco:o)
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1794. sky1989
Quoting SouthDadeFish:
And all those you listed actually recurved ;)


On the other end of the spectrum, I remember the GFS ultimately bringing the invest storm that would become Hurricane Bill into a Texas landfall in 2009.

While the models may not be good on predicting track in the long range, they are definately sometimes good at indicating favorable conditions for development.
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1793. pottery
Well, I'm out.
I have an early start to a busy day.
I need to find, and buy, a new shower curtain of a Particular Design......
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1791. GHOSTY1
Things are getting crazy, same name storms possible in the same area, wooooo weird, gotta see this happen.
Gotta go goodnight to everyone and be safe.
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1790. MTWX
Quoting AtHomeInTX:


I think Ike was the only long tracker of the 3. Could be wrong? On another note long tracking CV storms don't make it to Texas often. But when they do they cause problems for sure. Allen, Ike...

Ike was. The other two formed up just SE of Florida.
Member Since: July 20, 2009 Posts: 23 Comments: 1392
Quoting GHOSTY1:
the LBAR looks the best for intensification and the worst for some one who may be in her path if she becomes too strong.
interesting because the LBAR is a statistical model and it seems to be outperforming the more reliable dynamical models. Lol
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Dark red line is the consensus...



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Quoting Stormchaser2007:
6z should be interesting.



Models already trying to fish 91.. probably going to be intense when she spins up. Over the last two months, NCH TC Probability maps deeply favor EPAC and Carribean. Hasn't been much light blue over CV.
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I guess it's safe to say we can use The Imperial March as 91L's theme?
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The LBAR may have performed well with Don, but to be honest there are much better models to watch than the LBAR. I'd take the GFS and Euro any day over the LBAR. They are much more consistently accurate. the 00Z Euro run will be very interesting.
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1783. GHOSTY1
Quoting MTWX:


Looks strangly of Emily '05... weird


Thats ironic Major Hurricane Emily and possible Emily nearly at the same spot, what weakened the first Emily?
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Quoting GHOSTY1:
Everybody started looking on to the new invest and something may form right on our doorstep and we just now found it. wow this is gonna be an amazing year for developement it looks like.


Well, we had this similar setup in the SW Caribbean/extreme East Pacific last week when the D storm formed in the East Pacific. The East Pacific won that time and we'll have to see if it does again. It will probably focus more where the upward MJO is located at the time.
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1780. Patrap
Member Since: July 3, 2005 Posts: 419 Comments: 127377
1779. sky1989
Quoting SouthDadeFish:
And all those you listed actually recurved ;)


They did indeed, but MUCH further west than predicted.
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Quoting MTWX:


Looks strangly of Emily '05... weird
I'm just surprised this storm never got retired.
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The model to pay attention to is the LBAR, it has been the least bias so far this season. We are watching this one carefully incase we have to evacuate oil platforms in the Gulf of Mexico in week and a half.
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Quoting GHOSTY1:
thanks, just a question is about the same area as katrina, ike, and rita formed or were there origins further north?


I think Ike was the only long tracker of the 3. Could be wrong? On another note long tracking CV storms don't make it to Texas often. But when they do they cause problems for sure. Allen, Ike...
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1775. KEEPEROFTHEGATE (Mod)
i got a bad feeling we have seen nothing yet
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Climatology is against Emily. 2-3 weeks too early. Unless AGW and all that stuff means something.
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1773. pottery
Quoting CaicosRetiredSailor:
Evening Pottery,

I christened our current storm
Don Quixote
and am hoping that next will be
Emily Post
with good manners and the best etiquette
so as to bother no one!

I vote for you!
I hope you are right.
LOL
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1772. GHOSTY1
Everybody started looking on to the new invest and something may form right on our doorstep and we just now found it. wow this is gonna be an amazing year for developement it looks like.
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1771. MTWX
Quoting GHOSTY1:
thanks, just a question is about the same area as katrina, ike, and rita formed or were there origins further north?


Looks strangly of Emily '05... weird
Member Since: July 20, 2009 Posts: 23 Comments: 1392

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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.