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 OceanBlue78:


Honestly thats what I have thought the whole time...I think strong tropical storm to cat 1 hurricane just south of Brazoria county, the county I live in.


Thats what i said last night too.
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Quoting OceanBlue78:


Honestly thats what I have thought the whole time...I think strong tropical storm to cat 1 hurricane just south of Brazoria county, the county I live in.



It's also very possible that it could be a direct hit on freeport, perhaps even a little north of that.
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Quoting VAbeachhurricanes:
Woah does everyone see the numbers in the top right of all the posts? Thats a nice tool!
woah that's cool
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Quoting NotCircumventing:
Great another "tool" to have tool-measuring contest over.


Only if they do a tally of who had the most at the end of the day. Daily prize winners, that sort of thing.

And it wouldn't cause any sort of problems whatsoever. None. Whatsoever.

Don was just too small to play. Lot of heart but just too small. He is the Rudy of ND. The Doug Flutie of the NFL.
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does anyone have new data from the hurricane hunters?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Good example of tropical cyclone development during the downward phase. Typhoon Mo-an I believe..
Member Since: September 27, 2007 Posts: 1 Comments: 20546
Quoting NotCircumventing:
We will still have a TS at 2, track at 5 will be more north with same intensity forecast as 11. Landfall near Matagorda Bay.


Honestly thats what I have thought the whole time...I think strong tropical storm to cat 1 hurricane just south of Brazoria county, the county I live in.
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Quoting SLU:
This deserves a yellow circle



Indeed... I would expect one soon in 24 hours or so. That's my take on it as it would be closer to 50W and convection (in theory) should be a lot more prevalent and warmer waters to assist further on that.

SAL is currently the limiting factor



To its current favor... is under a decent shear environment and an ULAC is over it:

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Funktop shows Don trying to throw up some new green. He had lost the green earlier. Wonder if it will persist.
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Quoting ProgressivePulse:


pressure not falling or rising? how much longer is recon going to be there?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting NotCircumventing:
All this scrolling up to stroke my ego is really tiring.

Does a minus deduct points?


Gosh.. how the heck am I expected to earn a Gold Medal with this cockamamie scoring system?
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Quoting SLU:
This deserves a yellow circle



The little blip embedded in the dry settled airmass west of Africa or the little wavelet over the Antilles?
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Quoting TropicalAnalystwx13:
Visible satellite shows that Don is really struggling now, more so than expected. Winds are still indicative of a strengthening tropical storm, but the pressure...not so much. Unless Don builds some convection on its northern side, it won't get much stronger. The chances of this making it to hurricane status are very low, IMO.

BTW, cool new feature Wunderground.



Shear may lower some by tomorrow, which may help Don strengthen.

lets hope don maintains ts status until landfall. the hurricanes will come next month. is recon still investigating?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
530. Jax82
RIP Don, again.
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529. srada
Quoting VAbeachhurricanes:


Like this if... I hope it never happens...


or REPOST if you like...
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TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 60 MILES...95 KM
FROM THE CENTER.
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Visible satellite shows that Don is really struggling now, more so than expected. Winds are still indicative of a strengthening tropical storm, but the pressure...not so much. Unless Don builds some convection on its northern side, it won't get much stronger. The chances of this making it to hurricane status are very low, IMO.

BTW, cool new feature Wunderground.



Shear may lower some by tomorrow, which may help Don strengthen.
Member Since: July 6, 2010 Posts: 113 Comments: 31554
Quoting srada:


almost like facebook?? the horror!!


Like this if... I hope it never happens...
Member Since: September 6, 2007 Posts: 0 Comments: 6149
04L/TD/D



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522. srada
Quoting NotCircumventing:
Great another "tool" to have tool-measuring contest over.


almost like facebook?? the horror!!
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1:00 PM CDT Thu Jul 28
Location: 24.6°N 90.7°W
Max sustained: 45 mph
Moving: NW at 15 mph
Min pressure: 1005 mb
Member Since: July 25, 2011 Posts: 0 Comments: 1102
SUMMARY OF 100 PM CDT...1800 UTC...INFORMATION
----------------------------------------------
LOCATION...24.6N 90.7W
ABOUT 475 MI...765 KM ESE OF CORPUS CHRISTI TEXAS
ABOUT 430 MI...690 KM E OF BROWNSVILLE TEXAS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES
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519. SLU
This deserves a yellow circle

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Lets all hope it maintains tropical storm status
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Will the moisture from the north help Don to build convection? Anyone...
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Quoting NotCircumventing:
Great another "tool" to have tool-measuring contest over.


Mines gonna have a higher rating then yours!
Member Since: September 6, 2007 Posts: 0 Comments: 6149
I'm thinking of driving from orlando back home to pensacola beach to surf. Anyone know if the winds/weather are going to calm down friday-saturday? gas is too expensive to drive that far if the windsv are still blowing 20mph and destroying the groundswell!tia.
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12Z NGP/CMC/GFS pretty much agree now on P10L developing to some extent. Assuming it detaches from the Monsoonal TROF it'll be able to develop.

So far is has a decent 850MB VORT signature, but due to the broad nature of it... it will take take to consolidate and break off:

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NWS Houston posted this discussion update an hour ago:

Ts Don is currently located north of the Yucatan Peninsula of
Mexico and continues to move to the northwest at around 15 miles per hour.
With this track Don will move inland along the Texas coast
sometime late Friday night. At this time the greatest impact to
southeast Texas will be from higher rainfall chances. One to three
inches of rain are expected with this storm...with the higher
rainfall amounts expected across areas closer to Matagorda Bay. 38
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that 476 comment was a little off targtet me thinks
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Quoting PcolaDan:

?



nevermind i looked at the quote wrong my mistake, just forget i said anything. i'm sorry.
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Good afternoon all. I am one of many lurkers and seasonal posters etc. Well what can I say winter is boring here in Houston so I am usually here during hurricane season lol! I am hoping Don brings us some rain here to my suburb and surrounding areas. My fellow Texans and I need some rain big time. I do have to say though, if I have learned anything from these storms, is to never assume anything. These thing can weaken, and then it seems as soon as they hit the coast they intensify or just before, just as Ike did. And of course our little friend Humberto. My point? Expect the worse, prepare for the worse, and even if you over prepared oh well because the next storm is right around the corner. That, and because something weakens, that does not mean it is dead. It amazes me how people seem to think Don will go poof...hey..that little sucker held on through everything to get where he is now...so never count any tropical disturbance out. Well, I guess all we can do now is sit back, have fun, and pray this thing brings a ton of rain to us Texans!
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Me thinks Don is "Done" No time left. Big rain maker for a small area but better than none! Kinda wish it was here.

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Quoting HimacaneBrees:



Very wrong question to ask someone on this blog.

never mind :)
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Woah does everyone see the numbers in the top right of all the posts? Thats a nice tool!
Member Since: September 6, 2007 Posts: 0 Comments: 6149
Quoting cloudburst2011:


what? lolhow could that happen you sure thats what he said..


Yes, that is what he said.

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Quoting PcolaDan:


????WTF?????



Very wrong question to ask someone on this blog. What #476 was asking, i mean.
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The upward MJO phase will be here soon...
Member Since: September 27, 2007 Posts: 1 Comments: 20546
Quoting HimacaneBrees:
whoa # 476 that is way out of line.


Report it and move on...
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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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