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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Crown Weather is being Bullish. He is saying a cat 1 WILL hit Texas or possibly....a cat 2!
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293. 7544
Quoting OrchidGrower:
Re: #249, vapor image


Holy cow -- look at the spin in that Central-Atlantic wave!


91L soon ? when u think they will tag this one tia
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Quoting AtHomeInTX:
Our little Don not looking too strong today. I see a naked swirl racing more north than the convection. Here at the border I'm getting storms from the SW. Don't know what that says about the steering. But the rain is nice. :D



Just drove thru your area a few weeks ago on I-10 going and coming from La Berge casino resort in Lake Charles
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Quoting RitaEvac:
Nice spin in Central Atlantic, and the NW jump of Don




That might become a Monster for the Caribbean! They need to watch this close. CAPE VERDE is here now!
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Our little Don not looking too strong today. I see a naked swirl racing more north than the convection. Here at the border I'm getting storms from the SW. Don't know what that says about the steering. But the rain is nice. :D

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Some convection now...
Member Since: September 27, 2007 Posts: 1 Comments: 21264
Member Since: August 19, 2005 Posts: 5 Comments: 5405
277, that's the program I work with, it's ESRI ArcMap
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Quoting cat5hurricane:
click image for larger view and for link


As of 28 July 2011 0500 CDT, water levels along the Texas coast are near predicted. Winds are steady, with gust between 10 to 17 knots. Wind gusts upto 17 knots have been observed at USCG Freeport, TX. Barometric pressure is dropping across the region.

South Padre Is. USCG, TX Next predicted high tides are 1.24 ft (0.38 m) at 07/28/2010 06:45 CDT and 1.21 ft (0.37 m) at 07/29/2010 07:21 CDT.

Corpus Christi, TX Next predicted high tides are 1.66 ft (0.51 m) at 07/29/2010 05:26 CDT and 1.60 ft (0.49 m) at 07/30/2010 05:42 CDT.

Port Aransas, TX Next predicted high tides are 0.84 ft (0.26 m) at 07/28/2010 07:20 CDT and 0.82 ft (0.25 m) at 07/29/2010 12:08 CDT.

Port O'Connor, TX Next predicted high tides are 0.64 ft (0.20 m) at 07/28/2010 10:17 CDT and 0.62 ft (0.19 m) at 07/29/2010 11:02 CDT.


You need a newer image, the landfall has moved a tad north.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
don will beat TX
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Quoting xtremeweathertracker:
Here is the link to the Mimic imagery that RitaEvac posted in the old blog cant figure out how to put in in the blog!!! HELP!!!

Link
Click on " recent animation " then click past 72 hour animation At the bottom of the page ), then right click copy feature, go to wu blog click image , click paste then post.
Member Since: September 27, 2007 Posts: 1 Comments: 21264
Quoting OrchidGrower:
Re: #249, vapor image


Holy cow -- look at the spin in that Central-Atlantic wave!


Yup, it is easily seen on water vapor, and even better on TPW above^^. As i just noted convection is increasing, and i wouldn't be surprised if the crayons came out soon.
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Nice spin in Central Atlantic, and the NW jump of Don

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Quoting angiest:


The Classic Rock station in Houston apparently has someone with an odd sense of humour. Over the last few months, they have been playing Stevie Ray Vaughn's Texas Flood quite a bit.


Wishful thinking. My hubby says, "If its stupid and it works, then its not so stupid." LOL
Member Since: June 11, 2008 Posts: 0 Comments: 47
Any ideas when the 12Z late models will be available?
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Watch this wave very closely over the next few days, this is our next threat for development.
Member Since: July 8, 2005 Posts: 259 Comments: 24044
Quoting angiest:


Reservoir levels in SE Texas as of one week ago.


LAKE LIVINGSTON 96.3 PERCENT
LAKE CONROE 84.8 PERCENT
HOUSTON COUNTY LAKE 89.2 PERCENT
LAKE HOUSTON 72.1 PERCENT
LAKE SOMERVILLE 62.2 PERCENT
LAKE TEXANA 57.9 PERCENT

This should be updated later today

Choke Canyon (near Corpus Christi)
Water Level
211.39 FEET
Thursday, July 28, 2011
7:30:00 AM
Level is 9.11 feet
below full pool of 220.50

http://chokecanyon.uslakes.info/Level.asp
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Quoting SLU:
While Don continues to steal the headlines, let's not forget to spare a thought for this little "playette" in the Central Atlantic.

Big spin to it fer sure..
Member Since: September 27, 2007 Posts: 1 Comments: 21264
260. Our thinking is pretty much in agreement. Which is probably scary.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Re: #249, vapor image


Holy cow -- look at the spin in that Central-Atlantic wave!
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Quoting scott39:
Weaker-N Stronger-W


I can't really agree based on the steering charts. Unless it makes it to mid cat 1-cat 2 strength. Those charts would support a more westward motion, but that has always been above my high end. But even at that, what we might see is more northerly motion followed by a bend further west, much closer to the middle or upper Texas coast.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Hello, everyone. Just dropping in and checking on Don and giving my input on the tropics for the next few days. IMO, Don is unlikely to become a hurricane as he will struggle with moderate wind shear and dry air along most of its path. Due to his small size, he will be more susceptible to these elements. Don should still be watched very closely as he approaches the coast.

Elsewhere, I am keeping a close eye on P010L in the central atlantic which could become Emily down the road. Has a 1008mb low embedded along the wave axis with some very well defined cyclonic curvature. Convection needs to increase(it appears to be doing so) and it will likely be labeled our next invest.

Ill be back on later, gone for most the day.

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Here is the link to the Mimic imagery that RitaEvac posted in the old blog cant figure out how to put in in the blog!!! HELP!!!

Link
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Quoting TropicalAnalystwx13:


No, he is being sheared.


Hmmm.. what shear?? Please point out 20 knots or more shear on this map.




All I see is 5-10 knots.. Dry air is the factor with the storms fall.
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Quoting TropicalAnalystwx13:


5-10 knots.

Are you really suggesting that TS Don will erode to an open low because of the Northern shear or are you simply saying that the N shear is 5-10kts?
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257. jpsb
Quoting TropicalAnalystwx13:




Down in the box where you comment, there are buttons just above it. Bold, Italic, Link, and Image. Click image, and then enter the images link. Click okay, and then post your comment. That's how you post an image.
Thanks!
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Weaker-N Stronger-W
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Quoting NotCircumventing:
1500 Steering ... high eroding




That could allow more modest strengthening and stacking as Don pulls away from the shear axis.

Member Since: August 19, 2005 Posts: 5 Comments: 5405
NW jump

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Quoting NotCircumventing:
241 ...

We agree.


My thought remains Matagorda Bay to High Island, but I am prepared to trim the eastern edge of that off, maybe to Freeport. My western edge is about 50-80 miles up the coast from the approximate landfall forecast from the NHC (if you connect the tropical points with a straight line).
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting JrWeathermanFL:

Weaken to....?


5-10 knots.
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Quoting jpsb:
In the old blog Ritaevac post # 1595 posted a nice graphic of Don being pushed more north. Wish I knew how to get to the old blog so I could repost that.




Down in the box where you comment, there are buttons just above it. Bold, Italic, Link, and Image. Click image, and then enter the images link. Click okay, and then post your comment. That's how you post an image.
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Quoting NotCircumventing:


I have the link, too. Just never knew they had that product on there.

That is what drives me nuts about NHC track graphics is that the "background" doesn't remain static making it diffucult to gauge accuracy (with a graphic)

That map does that nicely and if you (eeek) XTRP the delta, then you see how these variances can make a true difference.


Like I said, It will be a sad day if we ever loose it.
Member Since: August 19, 2005 Posts: 5 Comments: 5405
Quoting floodzonenc:

Perhaps they were hoping it would be a self-fulfilling prophesy.  We are dry here in eastern NC, but NOTHING like what TX is dealing with.  You guys are definitely in my prayers.


Reservoir levels in SE Texas as of one week ago.


LAKE LIVINGSTON 96.3 PERCENT
LAKE CONROE 84.8 PERCENT
HOUSTON COUNTY LAKE 89.2 PERCENT
LAKE HOUSTON 72.1 PERCENT
LAKE SOMERVILLE 62.2 PERCENT
LAKE TEXANA 57.9 PERCENT

This should be updated later today
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting TropicalAnalystwx13:


10-20 knots of northerly shear. It should weaken somewhat as it heads NW.

Weaken to....?
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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.