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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Member Since: September 27, 2007 Posts: 1 Comments: 21209
BTW, since it got lost in the troll. I hope Dr. Masters explains his statement that this is Texas' worst drought on record. The most recent information I could find from the Texas State Climatologist says this is the third worst.

If memory serves, the worst was ca. 1919. But I don't have that information at hand.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting SurfYak:
I hope it brings some surfable waves to Galveston TX!


Id love to see some pictures of Galveston since 2008. Let me know if you have any...
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Will we get rain in Corpus from Don?
Member Since: August 30, 2008 Posts: 0 Comments: 287
I hope it brings some surfable waves to Galveston TX!
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It looks like the lizards and cactus are gonna get a nice bath.
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Quoting P451:


If you look intently at some image loops you will be able to see the surface circulation exposed. Focus particularly on the NW side and you can see the surface circulation heading NW.

The convection, which is being displaced due to shear, is tricking us into seeing a more westerly motion which is not actually occurring.



Oh, I wasn't disputing the motion, I just don't think it was expected. It could have some implications down the road if it lasts.

Note that pretty much the entire Tropical Storm Watch was replaced with a warning, not just a portion of it. Seems the NHC is hedging just a touch.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting P451:
Short Wave Imagery gives you a good look at Don's surface structure and movement.




Don's SSD Floater Page


That is a great view of actually where the LLC is located.......many think the swirl to the north was the LLC. That was actually the MidLevel that it spit out.
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so if it keeps that NW track the forecast track should also start shifting to the right more?
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Quoting RitaEvac:
convection casting here

Wish the convection would lean N and NE so Houston/Galveston areas would get some good rains
AMEN!!!!!!!!!!!!
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Just curious how strong will don be at the 2pm adivsory?

a: 40
b: 45
c: 50
d: 55
e: 60
also how much longer are the hurricane hunters going to be in don?
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well, there are no preperation being made in Corpus, it is business as usual.
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Looks like Don weakens before landfall..
Member Since: September 27, 2007 Posts: 1 Comments: 21209
convection casting here

Wish the convection would lean N and NE so Houston/Galveston areas would get some good rains
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Appropriate track shift as Don is way starboard(Right) of previous track.

Member Since: August 19, 2005 Posts: 5 Comments: 5405
Quoting RitaEvac:


NHC track will need to be nudged little north in next advisory


Yes...the ol' eyeball extrapolation from visual sat leads me north of NHC projection, and several have noted feelings of a more ~Matagorda area landing. Just don't forget to bring your "Camel Back" Don, and you'll be the life of the party!
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Quoting TampaSpin:


He is ignored in mine..........not sure why not yours!


I add him on my ignore list, and he was gone for a minute, but then he reappeared again.

EDIT: OHhhhhhhhhhh...I know what you are talking about now Angiest.
Member Since: July 6, 2010 Posts: 113 Comments: 32056
Quoting Orcasystems:


If they don't have a blog of their own set up.. then the ignore function does not work... they have to initialize their blog on WU


I did not realize that......thanks!
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What Don needs to do to reach strong tropical storm status is build convection over the northern side. After that, its centers need to re-align. After that, it will strengthen. Heck, maybe if it doesn't even do that, it will strengthen.
Member Since: July 6, 2010 Posts: 113 Comments: 32056
Quoting TampaSpin:


He is ignored in mine..........not sure why not yours!


If they don't have a blog of their own set up.. then the ignore function does not work... they have to initialize their blog on WU
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Quoting angiest:


Um, NW? Not WNW?

Yet I don't think the track actually changed. The current map on WU looks strange now.


OK, WU fixed the map. Looks like Corpus/Port Aransas area right now.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting P451:


Or talk about him. There's more posts about him than what he posted.

These clowns get us to derail the blog ourselves.

REPORT, IGNORE, DONT QUOTE, DONT DISCUSS.... is something we should all learn to do with these situations.



R.I.D.D. I like that acronym.
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Am I being ignored?
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165. HCW
Member Since: August 10, 2002 Posts: 0 Comments: 1408
troll removal complete

empty space created
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Thanks Jeff.
LoL, I'm late for the blog update again.
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Quoting angiest:


Um, NW? Not WNW?

Yet I don't think the track actually changed. The current map on WU looks strange now.


NHC track will need to be nudged little north in next advisory
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I'm off to work...later all.
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Quoting TropicalAnalystwx13:
10:00 AM CDT Thu Jul 28
Location: 24.1N 90.1W
Max sustained: 45 mph
Moving: NW at 14 mph
Min pressure: 1001 mb

Angiest, you beat us again!


Um, NW? Not WNW?

Yet I don't think the track actually changed. The current map on WU looks strange now.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Guys just forget about the troll and lets actually talk about don... the pressure rose and the winds picked up..
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What did I tell you guys earlier?

Guy has a hard on for this place. Just ignore it. Can't be that hard for you.....seriously.

I'm hoping the doc is right and Don can get enough moisture to get bigger but not too big. Good luck Texas.
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DeborahNagy

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Quoting TropicalAnalystwx13:
Why doesn't the person go on ignore when I add 'em to my ignore list. Does this mean he has hacked Wunderground?


He came with two different handles. Similar, but different, added a 1 to the end of it to bypass being banned the first time.
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Quoting TropicalAnalystwx13:
Why doesn't the person go on ignore when I add 'em to my ignore list. Does this mean he has hacked Wunderground?


Another troll account with almost the same name. Ignore the new one.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Guys the troll has been removed,but your defeating the purpose of the ban by quoting him,please don't quote him
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Quoting TropicalAnalystwx13:
Why doesn't the person go on ignore when I add 'em to my ignore list. Does this mean he has hacked Wunderground?


He is ignored in mine..........not sure why not yours!
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Quoting TropicalAnalystwx13:
10:00 AM CDT Thu Jul 28
Location: 24.1°N 90.1°W
Max sustained: 45 mph
Moving: NW at 14 mph
Min pressure: 1001 mb

Angiest, you beat us again!


Heehee.

BTW, for those not from the area. Although the spelling, San Luis, is Spanish, the correct pronunciation is: Loo-ee, more or less.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Vincent4989:

MORE TROLLS!

Don't feed the bears.
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Still support for the wave around 35W. Euro devlops it also - but peters it out mid Carib.

http://www.emc.ncep.noaa.gov/gmb/tpm/emchurr/tcge n/mgtracks.2011072800.html
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Quoting TropicalAnalystwx13:
10:00 AM CDT Thu Jul 28
Location: 24.1°N 90.1°W
Max sustained: 45 mph
Moving: NW at 14 mph
Min pressure: 1001 mb

Angiest, you beat us again!

the pressure rose yet the winds picked up.. interesting..
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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.