Tropical Storm Don unimpressive so far

By: Dr. Jeff Masters , 2:08 PM GMT on July 28, 2011

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Tropical Storm Don formed yesterday from an African tropical wave that crossed into the Gulf of Mexico, and the thus-far unimpressive storm appears poised to bring tropical storm conditions to the lower Texas coast by Friday night. An Air Force Hurricane Hunter plane arrived in the center of Don around 8am EDT this morning, and has found Don to be a small tropical storm with top winds near 40 mph. The 7:57am EDT center fix found a central pressure of 1002 mb, which is 2 mb higher than NHC was estimating in its 8am EDT advisory. However, a pass through the center at 9:49am EDT found the pressure had dropped 2mb, to 1000 mb. Top reliable surface winds seen by the Air Force plane with its SFMR instrument as of 9:45am EDT were 41 mph, at 8:10 am EDT. 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 10 - 15 knots of wind shear. The shear is from strong upper level winds out of the north. Since the atmosphere to the north of Don is relatively moist, the moderate shear will not be as damaging to the storm as if these winds had been blowing from the northwest, where the driest air lies. Thus the shear direction is often just as important as the strength of the shear, and in Don's case, the shear direction should not force significant amounts of storm-disrupting dry air into the core. Water temperatures in the Gulf of Mexico are near 29°C, which is 2.5°C above the 26.5°C threshold typically needed to maintain a tropical storm.


Figure 1. Morning satellite image of Don.

Satellite imagery shows that Don is a very small storm. Thus, the storm is vulnerable to pockets of dry air and modest-sized jets of wind shear that we can't see from the relatively coarse-resolution data collected by surface stations, hurricane hunter flights, and satellites. The moderate wind shear over Don is keeping Don's circulation tilted so that the surface center is displaced from the center at higher levels. This tilt is keeping the storm from intensifying. Latest visible satellite loops show a modest increase in the intensity of the thunderstorm's near Don's center began at 9am EDT, but this could be a transient burst and not a sign the storm is undergoing intensification.


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 be a boon or bane for Texas? The state is currently suffering through its worst drought in recorded history, and 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. However, we have a Goldilocks problem. We can't have Don intensifying into a hurricane, or its winds and flooding might bring hundreds of millions in damage. Neither do we 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. This forecast is low-confidence, though, since Don's small size makes it prone to sudden changes in strength, either upward or downward. NHC is giving Don just a 14% chance of intensifying into a hurricane in its 5am advisory, but this could easily change upward if Don manages to overcome its vertical tilt and start consolidating an eyewall. I put the odds of Don reaching hurricane strength at 30%. None of the computer models is predicting Don will become a hurricane.

A small system like Don is relatively difficult to resolve in some of the computer models we use to forecast tropical storm track, and the forecast tracks of Don from these models have a higher spread than usual. For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast, which is showing that Corpus Christi and Port O'Connor, Texas have the highest chance of 39+ mph winds: 40%.

I'll have a new post this afternoon.

Jeff Masters

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Quoting GHOSTY1:


Thats news to me, thanks for letting me know, doesnt that sound like they are thinking it may be stronger than a tropical storm or are they just being precautious?


It is a percaution. Here is the TAMUCC release to staff http://www.tamucc.edu/marcom/hurricane/assets/wea ther_update_7-28.pdf
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Sorry to deviate off Don, but the ECMWF is once again showing a tropical cyclone affecting Puerto Rico and Bahamas, but recurves it out to sea (good thing, because if not, it could get real strong. Could do that anyway).

Yes, it should be a TC, since its closed.

Member Since: July 6, 2010 Posts: 113 Comments: 32275
Quoting GHOSTY1:
NotCircumventing, i believe that is a good option but i think Rockport is the target so far it looks like, but im no meteorologist and u been bloggin for a couple years so u probly know more about educated guessing

I hope so. Rockport works for me-lots of our wildlife are dying. Fire Dept. came and hosed down the "Big" Tree at Goose Island to save it from death.
Member Since: July 15, 2005 Posts: 25 Comments: 341
Quoting TropicalAnalystwx13:
Best case scenario: Don grows in size and develops more deep convection. Moves into Texas as a strong TS/weak hurricane (they can take it), and gives a lot of the southern part of the state very beneficial rainfall. Then, it is picked up by a trough and sent back into the Gulf similar to TD #5 of last year, and moves west. It re-strengthens and becomes a big rain-maker and brings more rain to Texas.

Very Very unlikely though :(


your asking for the 2001 TS Allison scenario that one was a doozie for us in Houston
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Quoting thirdcoastguy:
I have been lurking for 2 years. We now have a storm headed my direction. I am located in the coastal bend of Texas in Victoria about 30 miles inland. We are definetely looking forward to some rain. We don't want a lot of the wind though. It appears our area will be in the northern quadrant, where the majority if rainfall is usually expected. I appreciate the great info from some of you over the past couple of years. Levi love your tidbits.
Cool! A fellow Victorian!! Really looking forward to some rain.
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72 hours..
Member Since: September 27, 2007 Posts: 1 Comments: 21416
Reason I say that Patrap is that the convection occurring in the N semi doesn't have the shear streamers that the clouds to the east of them have. And why convection is now there to begin with.

Member Since: August 19, 2005 Posts: 5 Comments: 5449
Please bring some rain to Corpus
Member Since: August 30, 2008 Posts: 0 Comments: 287
Quoting thirdcoastguy:
I have been lurking for 2 years. We now have a storm headed my direction. I am located in the coastal bend of Texas in Victoria about 30 miles inland. We are definetely looking forward to some rain. We don't want a lot of the wind though. It appears our area will be in the northern quadrant, where the majority if rainfall is usually expected. I appreciate the great info from some of you over the past couple of years. Levi love your tidbits.


You may be in the good area because most meteorologist predict rockport landfall and victoria isnt too far away so you may get some good rainfall totals i just hope we can get some here in houston too, Good luck!
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735. DFWjc
Quoting HCW:


I don't use Wipers cause I have a life time supply of aquapel . It's like Rain X on roids


Is it really worth the money??
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Quoting NOLALawyer:
Come on Don!
Jeez..Where ya been?
Member Since: September 27, 2007 Posts: 1 Comments: 21416
733. HCW
Quoting BrockBerlin:


Windshield wipers.


I don't use Wipers cause I have a life time supply of aquapel . It's like Rain X on roids
Member Since: August 10, 2002 Posts: 0 Comments: 1409
Come on Don!
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Best case scenario: Don grows in size and develops more deep convection. Moves into Texas as a strong TS/weak hurricane (they can take it), and gives a lot of the southern part of the state very beneficial rainfall. Then, it is picked up by a trough and sent back into the Gulf similar to TD #5 of last year, and moves west. It re-strengthens and becomes a big rain-maker and brings more rain to Texas.

Very Very unlikely though :(
Member Since: July 6, 2010 Posts: 113 Comments: 32275
NotCircumventing, i believe that is a good option but i think Rockport is the target so far it looks like, but im no meteorologist and u been bloggin for a couple years so u probly know more about educated guessing
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I have been lurking for 2 years. We now have a storm headed my direction. I am located in the coastal bend of Texas in Victoria about 30 miles inland. We are definetely looking forward to some rain. We don't want a lot of the wind though. It appears our area will be in the northern quadrant, where the majority if rainfall is usually expected. I appreciate the great info from some of you over the past couple of years. Levi love your tidbits.
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726. DFWjc
Quoting prcane4you:

Evacuate now.


For a TS?
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18z Early Cycle NHC model tracks
Don
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)




Dynamic Models (More sophisticated models)





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Quoting NotCircumventing:
DOOOOOM!!!!

It appears Houston is being affected by -- egads! -- rain!

Way to go, Houston! Sure hope you folks get a nice soaker from Don, or otherwise. Lord knows you deserve it.
There is a weak disturbance in La. that will give Houston and southeast Texas some rain not associated with Don at all
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I can't believe I'm saying this, but the CLIP suite looks most believable at this time:

Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Patrap:
Whats left of the CDO is still being Shunted Sw by the Neast sheer,,as the CoC moves off to the Nwest.




Don has turned around over the past hour or so. As ProgressivePulse said, convergence and divergence are becoming more aligned. Not only that, but deep convection is starting to fire on the northern half of the system.

Whatever you said isn't going to last much longer.
Member Since: July 6, 2010 Posts: 113 Comments: 32275
719. BA
Quoting GHOSTY1:


Thats news to me, thanks for letting me know, doesnt that sound like they are thinking it may be stronger than a tropical storm or are they just being precautious?


It may be procedure anytime a tropical storm warning or higher is issued...I'm not sure what their policy is.

Sucks really bad for students that don't have a place to stay though.
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Not for long IMO, Patrap.
Member Since: August 19, 2005 Posts: 5 Comments: 5449
Quoting prcane4you:

Evacuate now.


LOL, i live in NW Houston and the only thought of evacuation before was Ike and Rita, Rita made Houston go into a complete frenzy US 290 was stalled out because so much traffic and Ike just made a gigantic mess with trees and power lines here
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GOES-12 GOM Viz Loop
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715. HCW
Latest NHC model runs for Don. Have a great day :)


Member Since: August 10, 2002 Posts: 0 Comments: 1409
Quoting NotCircumventing:
Has anyone mentioned Matagorda, TX (or so) as probable landfall location?

If not, they should.


I believe you have mentioned Matagorda about 3000 times already. Give it a rest.
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Member Since: September 27, 2007 Posts: 1 Comments: 21416
Quoting NotCircumventing:
Has anyone mentioned Matagorda, TX (or so) as probable landfall location?

If not, they should.


Over 24 hours ago.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Whats left of the CDO is still being Shunted Sw by the Neast sheer,,as the CoC moves off to the Nwest.


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Quoting BA:


yes, tamucc, they announced it on the local news


Thats news to me, thanks for letting me know, doesnt that sound like they are thinking it may be stronger than a tropical storm or are they just being precautious?
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No doubt Don has reversed course. Convergence/Divergence more aligned with the cyclone and in response Don is pulling back in the convection to the S. Not to mention what's now going on in the N Semi.


Member Since: August 19, 2005 Posts: 5 Comments: 5449

Quoting MississippiWx:
Wow, the Atlantic has become very warm in the past week. It is now warmer than this time last year.

July 27, 2010:



July 27, 2011:

Fish like's warm waters
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Quoting JamesGalloway:
I've been looking at wind shear forecasts and have a question. I understand the concept of wind shear, but can someone explain to me what is shown on a "wind shear forecast" map versus what is shown on a "zonal wind shear forecast" map.

Thanks.


Zonal normally refers to east-west. Explained Link
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704. BA
Quoting GHOSTY1:


Are you talking about the CC Texas A&M campus? because my cousin goes there and i haven't heard any thing about evacuations.


yes, tamucc, they announced it on the local news
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Looking at visible images, (rapid scan rocks) TS Don is moving into an area of much relaxed shear compared to the east. A round of intensification is looking likely in the next 6 hours, next HH should find a 55-65mph TS.
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Floater - RGB Color Infrared Loop


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Quoting angiest:


Looks like he wants to pull something in from the north.
thats what we want
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Quoting GHOSTY1:
I heard on our houston radio news 740 KTRH that they think landfall maybe between Corpus Christi and Rockport, TX
Evacuate now.
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Quoting BA:
it's easy for ppl that don't live on the coast (that is to be impacted) to wish for storms to fire up, etc etc...

for those that live in the affected area, even a small tropical storm disrupts all sorts of businesses and organizations (people)...they are not a very friendly way to get rain

I, for one, hope Don doesn't strengthen at all...they are already evacuating Texas A&M campus...so kids with no place to go have to take a bus all the way to Laredo


Are you talking about the CC Texas A&M campus? because my cousin goes there and i haven't heard any thing about evacuations.
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Quoting TropicalAnalystwx13:
Don firing deep convection once again, and according to ATCF, no change in pressure since 12Z (1001 mb.). Could this be the start of Don's intensification? Possibly, but it is a little too early to see yet. Multiple outflow boundaries are seen coming from the system, which means that the main problem that Don is having is dry air.



you are certainly correct. dry air will be its problem until landfall shear however will become MUCH weaker for it tomorrow. has the potential to be a moderate/ strong ts 50-65mph not a hurricane but still a nice ts
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting tiggeriffic:
hydrus or jason...popped on for just a few...don't have long...could either of you post a map of what the high is doing over the US please...thanks in advance
This is 24 hours out.
Member Since: September 27, 2007 Posts: 1 Comments: 21416
Quoting angiest:


Leaving home this morning there was a beautiful cloud well to the east, backlit. I never looked up the radar but it certainly resembled a CB. Too bad I wasn't in a position to get a picture of it.


Awwww, I missed that. I am anticipating some great cloud shows in the next few days.
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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.