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 MiamiHurricanes09:
Don's current structure reminds me of Fiona from last year.

Conditions were somewhat similar.


And she peaked at 65 mph. Very possible at this time.
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220. Daveg
Question... the models seem to be bouncing back and forth from more northward to more southward.

What would be causing them to do that, and it is likely that the NHC track will tend to stay more where it is unless the tracks stop that back and forth?
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Quoting GHOSTY1:


And i expect that number to steadily increase because some people just don't see the whole picture that he's moving into favorable environment and will strengthen and possibly weaken but its not over till its over.


I agree it has survived everything so why would it die now
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Tropical Storm Don seems to be slowly intensifying and improving this evening as convection has been building and has been taken on a more rounded structure and the outflow pattern has become more evident around the storm. Still dealing with some slight wind shear and dry air, but should intensify some overnight.
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217. j2008
Quoting weatherh98:


I'm thinkin that's at least 50 mph

Im going to stick by my prediction of 55 by 8pm
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Quoting KEEPEROFTHEGATE:
may mean a big slip coming

If they were the only 2 shakes in 2 days, probable...
But we've been having an average of maybe 7 shakes per day, and that releases energy, bit by bit..
But, we never know... when it will happen..
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Quoting weatherh98:
we are at 2133


And i expect that number to steadily increase because some people just don't see the whole picture that he's moving into favorable environment and will strengthen and possibly weaken but its not over till its over.
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Quoting Patrap:
Yeah baby..!


Floater - Rainbow Color Infrared Loop



Zoom,Boxes and Tropical Points active


I'm thinkin that's at least 50 mph!!!!!!
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Quoting sunlinepr:
4.0 and 4.3 today from a total of 9 today

may mean a big slip coming
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Quoting GHOSTY1:


And their right i believe it will be and i have never left that stance and wont till landfall most everyone on here see's a weakness in Don then they say he's dead, how many times can you keep calling him dead when he's still alive and kicking?
we are at 2133
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Don needs to keep up the pace he's at now it seems he is pulling himself together and intensifying we just gotta wait and see.
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Low-level center becoming better aligned with the deep convection. A sign that Don is trying to strengthen some more.
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Don's current structure reminds me of Fiona from last year.

Conditions were somewhat similar.
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Quoting KEEPEROFTHEGATE:
04L/TD/D
on approach

Looking a LOT better now!
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Quoting hurricanehunter27:
I bet in an hour people will be saying hurricane again!


And their right i believe it will be and i have never left that stance and wont till landfall most everyone on here see's a weakness in Don then they say he's dead, how many times can you keep calling him dead when he's still alive and kicking?
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4.0 and 4.3 today from a total of 9 today

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04L/TD/D
on approach

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Yeah baby..!


Floater - Rainbow Color Infrared Loop



Zoom,Boxes and Tropical Points active
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Quoting KaNaPaPiJoSa:


I know they are safe where they are. I was throwing it out as a bit of comic relief (didn't mention anything about the ex wife's safety)
Was sooo tempted to ask you about that!
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Quoting GHOSTY1:


Don will more than likely be something weak so they will be safe, we got a 2nd house down there and we're not to worried


I know they are safe where they are. I was throwing it out as a bit of comic relief (didn't mention anything about the ex wife's safety)
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Quoting VAbeachhurricanes:


Hey Storm! What happened to the website?!


Godaddy messed up when I renewed the server, but I'm about to shut it down anyway. I may put it back up on a cheaper server one day, but $500 a yr is way more server than I need for what I have on there. Plus I am going to be slammed for the next yr with school. In the fall, I'm taking 21 credit hrs.

I miss the site too though.
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TS Don Floater - RGB Color Infrared Loop
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I bet in an hour people will be saying hurricane again!
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Serious watch Mid Atl
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It looks like Don may be ready to get back goin' and off to the races im forecasting increasing strength
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TS Don Shaking off the shear,,has kinda stacked the column again,and is taking advantage of it..

Groovin baby'

Viz



RGB


Rainbow
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192. j2008
Quoting charlottefl:


It is under the convection, "completely", depends on how you use the word. It is towards the northern end of the convection, so it's not a good setup for steady strengthening. (still struggling some with wind shear) It really needs to be in the center of the convection.
He is looking better though. If he can continue the trend he should begin at least some slow intensification.

Glad I wasnt seeing things. Thanks for conferming, Its still a lopsided system but it looks much better than it has in the past and is on its way to minimal strengthening of about 60 at landfall IMO.
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Quoting KaNaPaPiJoSa:


My ex wife and kids live in Rockport. I hope the kids are safe.


Don will more than likely be something weak so they will be safe, we got a 2nd house down there and we're not to worried
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Quoting CybrTeddy:


That remains the only inhibiting factor of development imo, which is why I do not believe it will develop until just before it reaches the islands.

I agree, but it does look like all the models are in agreement. We should have a system near the northen islands in a wetter environ.
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Upward MJO should be over the Atlantic during the last few days of this month into the first few days of August. Again this season, you can tell how the upward pulse doesn't like to go to any other basin. It wants to stay in the anomalously warm Atlantic. Any prolonged downward MJO forecast by the models should be discounted. None of them show a prolonged downward motion over the Atlantic now like they did a few days ago.





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Quoting GHOSTY1:


My family and i have 2nd house down there and go quite often but havent been there to the mansion but we like rockport alot and the lighthouse inn.


Take a tour and ask the guide how high the water got in the mansion in 1919. Then realize how far above the Bay the mansion was built.
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Quoting KaNaPaPiJoSa:


My ex wife and kids live in Rockport. I hope the kids are safe.


OUCH...
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Quoting j2008:
I think i'm looking at this right, but I would swear that Don's crculation is compleatly under convection and hes starting to band now. The loop imagery looks like he should be a 55 MPH storm now. Just my opinion, somebody point out some pointers to explain if im wrong.


It is under the convection, "completely", depends on how you use the word. It is towards the northern end of the convection, so it's not a good setup for steady strengthening. (still struggling some with wind shear) It really needs to be in the center of the convection.
He is looking better though. If he can continue the trend he should begin at least some slow intensification.
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Quoting scott39:
I posted the same thing earlier. Great minds think alike:)


True that.
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Quoting GHOSTY1:
Im still for a Rockport landfall just north of CC


My ex wife and kids live in Rockport. I hope the kids are safe.
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Quoting angiest:


If that happens, at least he shouldn't be strong enough to mess up the hotel we stay at in Fulton. It is right across from Fulton Harbor.

If you ever find yourself in the Rockport-Fulton area (assuming you haven't ever done this), visit Fulton Mansion. About 2 blocks back from the mansion (on what used to be the same property) there is a big oak tree in the front yard of what may be an abandoned house. In that tree is a very unusual object: The "wheel" of a windmill, blades and all. It was deposited there by the 1919 Corpus Christi hurricane.


My family and i have 2nd house down there and go quite often but havent been there to the mansion but we like rockport alot and the lighthouse inn.
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2 Feet of Snow Slams South Africa

Link
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Quoting GHOSTY1:
Im still for a Rockport landfall just north of CC
I posted the same thing earlier. Great minds think alike:)
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179. j2008
I think i'm looking at this right, but I would swear that Don's crculation is compleatly under convection and hes starting to band now. The loop imagery looks like he should be a 55 MPH storm now. Just my opinion, somebody point out some pointers to explain if im wrong.
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Quoting StormJunkie:


Yeah, agree completely...But the deal was people would give money to disaster relief if I ate something like 15 of them in two hours...Without throwing up.


Ahhh.

I couldn't even down one Krystal "burger."
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Quoting StormJunkie:


Yeah, agree completely...But the deal was people would give money to disaster relief if I ate something like 15 of them in two hours...Without throwing up.
Ate one once while stationed in Pcola, bad times, would eat Checker's any day.
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Quoting GHOSTY1:
Im still for a Rockport landfall just north of CC


If that happens, at least he shouldn't be strong enough to mess up the hotel we stay at in Fulton. It is right across from Fulton Harbor.

If you ever find yourself in the Rockport-Fulton area (assuming you haven't ever done this), visit Fulton Mansion. About 2 blocks back from the mansion (on what used to be the same property) there is a big oak tree in the front yard of what may be an abandoned house. In that tree is a very unusual object: The "wheel" of a windmill, blades and all. It was deposited there by the 1919 Corpus Christi hurricane.
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Quoting StormJunkie:


Yeah, agree completely...But the deal was people would give money to disaster relief if I ate something like 15 of them in two hours...Without throwing up.


Hey Storm! What happened to the website?!
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Don is over PINK waters in the GOMEX. pink is high 80's like 88 89. shear is weakining too. don should be at 60 65mph b4 landfall
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Quoting angiest:


Krystal? Blech. Five Guys. Or Smashburger. Or Moo Yah.


Yeah, agree completely...But the deal was people would give money to disaster relief if I ate something like 15 of them in two hours...Without throwing up.
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Looks like the COC is starting to get tucked under the convection. Northeasterly shear has let up just a touch based on sat images. Not sure if it'll stay that way, but it's helping with the current organization trend. Dry air may still be a problem, it's very slowly starting to mix out. If Don can establish it's inner core I think it'll start to take off, but that's a big "?" right now.
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Quoting cchsweatherman:


Notice all the stratocumulus clouds surrounding the entire wave to the north. Very indicative of a stable, dry environment.


That remains the only inhibiting factor of development imo, which is why I do not believe it will develop until just before it reaches the islands.
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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.