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 NotCircumventing:
Maybe a name change to TS Done?

Don ain't done yet, Nice loop here to check out.
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Fish Storm? Just because models show a trough doesnt mean its going to be a fish storm.. euro showed don it like 3 runs recurving and now its hitting texas. stop saying fish storm unless the storm actually forms... Now can someone tell me if don is weakining or stregnthininh
Member Since: July 25, 2011 Posts: 0 Comments: 1102
The pressure has not risen in Don yet this morning its just the dropsond found the pressure at 1005 the planes radar still has it at 1002
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Outflow boundaries very evident to the north of the system, not good for Don.
Member Since: September 6, 2007 Posts: 0 Comments: 6704
12Z GFS decouples Don's 500mb circulation and sends it due W. If something doesn't change here that may not be all that unreasonable. Can't jump to conclusions, as I still think he will pull himself together, but wanted to say its definitely a possibility.
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Quoting hydrus:
What remarkable coincidence. The exact same thing happened to me..As far as the trough, it is all timing anyway , the troughs will be coming and going, not just one trough hangin off the east coast..Thats what the models are indicating at this time..Models change frequently and so do the weather patterns. ( Very quickly sometimes ).


Then you know how that person feels too. Lol. Yeah I agree. Timing's everything! The last few hurricanes through here were both supposed to go to my sw on the coast then a front wisked them up and away at the last minute. Well maybe not Humberto. I think he would come under weather quickly changing! Lol.

On the other hand this drought pattern has been hanging on tooth and nail.
And now there's talk of La Nina coming back for winter/spring. Sigh. If the Dons can't bring any relief, I'm starting to get scared thinking bout what would. Come on DON! Get your act together! :)
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Quoting DFWjc:
Hey Patrap, what do you think of this Hurricane tracker?

http://www.msnbc.msn.com/id/43919564/ns/weather/




Not a bad one atall.
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388. DFWjc
Quoting NotCircumventing:
If this was last year, we might hear the Price is Right Losing Horn right now.


Link
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Quoting Chicklit:
I believe we are approaching active part of hurricane season. Hoping Don is not too weak and not too strong. Welcome back Dr. Masters!!!

Link

That is one heck of a wave in the central atlantic.
Bet the guys at NHC are stocking up on coffee as we speak.

Would someone please enlighten us about the MJO and its affect on that CATL wave?
Hello chicklit. We are in a downward phase..This link is excellent...Link
Member Since: September 27, 2007 Posts: 1 Comments: 22626
Quoting Patrap:


Looks like a S
Member Since: September 6, 2007 Posts: 0 Comments: 6704
384. DFWjc
Hey Patrap, what do you think of this Hurricane tracker?

http://www.msnbc.msn.com/id/43919564/ns/weather/
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Here is the latest Graphics and Complete Update:


http://www.wunderground.com/blog/TampaSpin/show.h tml
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Quoting hurricanehunter27:
Not always true, Alex had pressure of 946mb but winds of only 110.


No, I'm saying that it takes a while for the winds to catch up to pressure, whether up or down. Just like with Alex, the winds just didn't have time to catch up with the pressure since it bombed off the coast.
Member Since: September 6, 2007 Posts: 0 Comments: 6704
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Quoting hurricanehunter27:
Ok i just got my new net installed, it is now 20mb instead of 150kb, probleme is its very hit and miss cause of the crappy router they gave me, if anyone can tell me what is the best router i would appercate it.


linksys wireless N router is great.
Member Since: September 6, 2007 Posts: 0 Comments: 6704
Quoting TropicalAnalystwx13:


No, recon confirms a system that, while its pressure is rising, it is also gaining in strength.

50 mph observed, not contaminated.


Looks like some new storm tops are begining to fire around the eastern and northeast flank of Don. Sign of maybe shear relaxing. I also have to believe that shear is actually stronger than what the instruments are picking up on. I have a hard time believing 10 knot shear is decoupling this system like it has in the last 6 hours. I'd say its at least around 20 knots.

We will see how his new thunderstorms organized and if shear relaxes. Still could see a minimal hurricane easily IMO.
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Quoting VAbeachhurricanes:


Its the pressure that matters, winds follow pressure, not the other way around.
Not always true, Alex had pressure of 946mb but winds of only 110.
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NEXT!!
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Ok i just got my new net installed, it is now 20mb instead of 150kb, probleme is its very hit and miss cause of the crappy router they gave me, if anyone can tell me what is the best router i would appercate it.
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Quoting TropicalAnalystwx13:


No, recon confirms a system that, while its pressure is rising, it is also gaining in strength.

50 mph observed, not contaminated.


Its the pressure that matters, winds follow pressure, not the other way around.
Member Since: September 6, 2007 Posts: 0 Comments: 6704
Level Geo. Height Air Temp. Dew Point Wind Direction Wind Speed
1007mb (29.74 inHg) Sea Level (Surface) 27.4°C (81.3°F) 26.6°C (79.9°F) 140° (from the SE) 37 knots (43 mph)
1000mb 66m (217 ft) 26.6°C (79.9°F) 26.1°C (79.0°F) 130° (from the SE) 37 knots (43 mph)
925mb 753m (2,470 ft) 23.0°C (73.4°F) 22.5°C (72.5°F) 135° (from the SE) 38 knots (44 mph)
850mb 1,491m (4,892 ft) 20.0°C (68.0°F) Approximately 12°C (54°F) 140° (from the SE) 31 knots (36 mph)

They couldve gone even higher, the dropsonde came up with 1007mb.
Member Since: September 6, 2007 Posts: 0 Comments: 6704
Quoting aquak9:


All the king's horses and all the king's men....
couldnt put my fat butt together again! Oh we were talking about 90L. LOL
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Quoting Patrap:
RECON confirms a decoupled weakened TS


No, recon confirms a system that, while its pressure is rising, it is also gaining in strength.

50 mph observed, not contaminated.
Member Since: July 6, 2010 Posts: 113 Comments: 32824
Floater - Visible Loop
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Quoting floridaboy14:
Wait don's pressure is rising? thats bad.


Yes, Don's pressure is rising. But, its winds are also going up. 50 mph surface winds recorded in the latest pass.
Member Since: July 6, 2010 Posts: 113 Comments: 32824
RECON confirms a decoupled weakened TS
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Quoting scott39:
Right now Don looks like an egg that someone thru against a wall. Maybe he will pull himself together.


All the king's horses and all the king's men....
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Wait don's pressure is rising? thats bad.
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting AtHomeInTX:


This kind of looks like last year. I guess we might sneak one into TX here but we'll have to see how many make through the troughs again.

Last time I said something like that I got an irate WUmail. To that person there's no need to respond. I got your opinion on the matter loud and clear! Lol.
What remarkable coincidence. The exact same thing happened to me..As far as the trough, it is all timing anyway , the troughs will be coming and going, not just one trough hangin off the east coast..Thats what the models are indicating at this time..Models change frequently and so do the weather patterns. ( Very quickly sometimes ).
Member Since: September 27, 2007 Posts: 1 Comments: 22626
Quoting TropicalAnalystwx13:
Don't be surprised to see 91L within the next 48-72 hours or sooner...This is one mean wave.



I wouldn't be surprised either. That's a decent-lookin' wave.
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Well, this is interesting. While Don's pressure is rising, its winds are also rising.
Member Since: July 6, 2010 Posts: 113 Comments: 32824
Pessure is up to 1005
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 28th day of the month at 16:15Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number & Year: 04L in 2011
Storm Name: Don (flight in the North Atlantic basin)
Mission Number: 2
Observation Number: 11
A. Time of Center Fix: 28th day of the month at 15:48:40Z
B. Center Fix Coordinates: 24°15'N 90°19'W (24.25N 90.3167W)
B. Center Fix Location: 396 miles (638 km) to the S (182°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,458m (4,783ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 45kts (~ 51.8mph)
E. Location of the Estimated Maximum Surface Wind: 86 nautical miles (99 statute miles) to the NE (48°) of center fix
F. Maximum Flight Level Wind Inbound: From 150° at 52kts (From the SSE at ~ 59.8mph)
G. Location of Maximum Flight Level Wind Inbound: 70 nautical miles (81 statute miles) to the NE (48°) of center fix
H. Minimum Sea Level Pressure: 1005mb (29.68 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,524m (5,000ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 24°C (75°F) at a pressure alt. of 1,524m (5,000ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 9°C (48°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1 nautical mile
Remarks Section:
Maximum Flight Level Wind: 52kts (~ 59.8mph) in the northeast quadrant at 15:26:00Z
--

wow, major weakening all the way up to 1005mb
Member Since: September 6, 2007 Posts: 0 Comments: 6704
When the Waves get a lil more west,,the Invest Status wil come,,its not important yet,,as they way out.

Time is on their side as well.
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i getting the feeling we will have nothing but a naked swirl by the end of the day here
Member Since: July 15, 2006 Posts: 178 Comments: 56059
When do you folks think we'll get 91L out around 40W?
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Itsa long way out I know..but it is almost that time..
Member Since: September 27, 2007 Posts: 1 Comments: 22626
Neast shear is the Limiting Factor..as of now seems to my obs.


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Quoting Patrap:
Dons center Motion is really coming right to NW,,or slightly NNw
spit'n out his llc
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Quoting hydrus:
Its a long way out, ( Aug-12 ), but this would be a monster trough for August...


This kind of looks like last year. I guess we might sneak one into TX here but we'll have to see how many make through the troughs again.

Last time I said something like that I got an irate WUmail. To that person there's no need to respond. I got your opinion on the matter loud and clear! Lol.
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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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