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 HimacaneBrees:
whoa # 476 that is way out of line.


Report it and move on...
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Quoting niederwaldboy:
#465--- In your avatar,


BAHAHAHAHAHA, OMG did you really just say that?
Member Since: September 6, 2007 Posts: 0 Comments: 6705
im hoping don hangs on to tropical storm stregnth until landfall hurricane is unlikely at this point even a strong ts is unlikely probably a peak at 50mph. its the dry air thats killing it
Member Since: July 25, 2011 Posts: 0 Comments: 1102
492. BA
Quoting roxycc:
well someone still thinks Don is going to produce, Texas A & M University Corpus Christi is shutting down at 5pm today and remaining closed till Monday morning.


not just shutting down, evacuating, anyone that has no place to go will be sent on a bus to Laredo campus
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Hope things thing stays weak but brings lots of rain to them but not too much to cause trouble.
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 28th day of the month at 17:27Z
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: 16
A. Time of Center Fix: 28th day of the month at 17:04:50Z
B. Center Fix Coordinates: 24°22'N 90°33'W (24.3667N 90.55W)
B. Center Fix Location: 389 miles (626 km) to the S (184°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,475m (4,839ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 40kts (~ 46.0mph)
E. Location of the Estimated Maximum Surface Wind: 15 nautical miles (17 statute miles) to the SE (129°) of center fix
F. Maximum Flight Level Wind Inbound: From 175° at 30kts (From the S at ~ 34.5mph)
G. Location of Maximum Flight Level Wind Inbound: 27 nautical miles (31 statute miles) to the SE (131°) of center fix
H. Minimum Sea Level Pressure: 1005mb (29.68 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°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 1,519m (4,984ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 10°C (50°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, Radar, 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 Outbound: 30kts (~ 34.5mph) in the northwest quadrant at 17:12:00Z
Member Since: September 6, 2007 Posts: 0 Comments: 6705
Good Afternoon...
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Quoting niederwaldboy:
#465---


????WT!????
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whoa # 476 that is way out of line.
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Shear and dry air is hurting Don more than I thought. Yesterday I was thinking he would get to Cat1, maybe even Cat2, now I doubt he will even reach hurricane status. Maybe my eyes are fooling me, but it seems that the surface flow is trying, but failing, to decouple the LLC from the convection
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Quoting cloudburst2011:



DON did affect hispaniola when he was down in the caribbean..he was right..


He said it would hit Hispaniola yesterday...
Member Since: September 6, 2007 Posts: 0 Comments: 6705
Quoting cloudburst2011:



DON did affect hispaniola when he was down in the caribbean..he was right..


No, he said that when it was entering the Gulf. That it was moving SE and going to die on Hispaniola.
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I need therapy for Don burnout.
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Hah. Pandora just brought up "Rock You Like a Hurricane." It's never come up on this station for me before.
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Quoting VAbeachhurricanes:


And start moving South East...

And didn't give any reasoning in his forecast.
Member Since: October 17, 2010 Posts: 0 Comments: 1267
now new information from the recon?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Lates on the HH Dropsond 1005mb pressure at the center Don has not weakened since the previos pass
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Quoting angiest:


He also said it was going to Hispaniola.


And start moving South East...
Member Since: September 6, 2007 Posts: 0 Comments: 6705
Quoting robie1conobie:
Wow! looks like lucreto calling for this storm to fall apart yesterday wasn't that off after all. We were all calling him a troll and thinking he was crazy.


He also said it was going to Hispaniola.
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471. j2008
IMO I dont think it will be down graded. The winds are still riseing even if the pressures have risen slightly too. I think everyone is slightly exagerating this. As has been pointed out, these small storms are pretty unpredictable. Don still can surprise us I have a feeling. Its JMO though.
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well someone still thinks Don is going to produce, Texas A & M University Corpus Christi is shutting down at 5pm today and remaining closed till Monday morning.
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Quoting hurricanehunter27:
Not always true, Alex had pressure of 946mb but winds of only 110.
That was because of Alex's large size. The larger the system, the lower pressures you need to achieve the same wind speeds that could be found in a smaller system. Alex was a large system, and therefore had a relatively low minimum central pressure compared to his max winds..
Member Since: August 24, 2010 Posts: 19 Comments: 4358
Complete Update

TS BUSTED FORECAST ALIBI





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anyone have any info from the Hurricane hunters?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Wow! looks like lucreto calling for this storm to fall apart yesterday wasn't that off after all. We were all calling him a troll and thinking he was crazy.
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Quoting hydrus:
I hate when it does that....


the link didnt open for you?
Member Since: August 19, 2006 Posts: 13 Comments: 16225
Quoting ncstorm:
12z NOGAPS..

Link
I hate when it does that....
Member Since: September 27, 2007 Posts: 1 Comments: 22684
anyone have new data from the hurricane hunters on don?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
The planes pressure is now at 1003 a 1 mb rise from the last pass
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458. xcool
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Oh ya.........i got live WebCams of South Texas up on the Site for you all when it is needed. Enjoy!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting TampaSpin:
Ok i am out..........gotta get oil changed and ready for my vacation next week.........got to HOT INDIANA to visit my mother. Sure wish the weather would break from the heat up there. Who would think i would be driving out of Florida to Indiana and i would complain about the heat in August next week..........WOW!


Haha welcome to my home Tampa! Its going to be in the high 90s today with a heat index of 105-110 degrees, with about 80% humidity
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...
BULLETIN
TROPICAL STORM DONe

?perhaps?
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(repost from last page, but thought i was note worthy for those who follow storms in both basins)
Let's not forget about our friends in the WPAC dealing with Tropical storm Nock-Ten, and Tropical Storm Muifa. Nock-Ten is poised to make a second and third landfall! Meanwhile Muifa is expected to threaten Japan as a formidable typhoon in the long range. Track is sure interesting on Muifa making a "S" like motion.

Both impressive on satellite imagery.






Member Since: October 17, 2010 Posts: 0 Comments: 1267
451. ncstorm
5:11 PM GMT on July 28, 2011
12z NOGAPS..

Link
Member Since: August 19, 2006 Posts: 13 Comments: 16225
450. TampaSpin
5:11 PM GMT on July 28, 2011
Ok i am out..........gotta get oil changed and ready for my vacation next week.........got to HOT INDIANA to visit my mother. Sure wish the weather would break from the heat up there. Who would think i would be driving out of Florida to Indiana and i would complain about the heat in August next week..........WOW!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
449. aussiecold
5:10 PM GMT on July 28, 2011
OK
Member Since: August 3, 2009 Posts: 0 Comments: 138
448. TomTaylor
5:09 PM GMT on July 28, 2011
Quoting yoboi:


it will be a fish storm
for what the US?

The wave, or whatever develops out of it, will heavily interact with the Caribbean islands. Should reach the lesser Antilles around Mon/Tue, and then head more WNW and interact with the greater Antilles as the Azores/Bermuda high is weakened. Also, you can't rule out the possibility of some interaction with the US, should it develop of course.
Member Since: August 24, 2010 Posts: 19 Comments: 4358
447. IceCoast
5:09 PM GMT on July 28, 2011
Quoting Levi32:


Wrapped-up dry air and broadness of the wave. This is just like pre-Don, which had no chance east of the islands, but flared up farther west. This one may do the same kind of thing.

Later.


Thanks. I definitely noticed the broadness of the wave and that it would take a while to wrap up, but i never looked at WV imagery. Still a lot of dry air to contend with out there.
Have fun at class.
Member Since: October 17, 2010 Posts: 0 Comments: 1267
446. TampaSpin
5:09 PM GMT on July 28, 2011
Quoting DFWjc:
I'm jealous TampaSpin, it's looks great outside!!!!



Sorry you need the Rain i know!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
445. hydrus
5:08 PM GMT on July 28, 2011
I know this has been posted a few times today, but there is something noteworthy here. Look how much moisture the low pressure area associated with this wave is wrapping into its circulation. It is tapping the monsoon trough plus a nice slug that is over the South Atlantic.This should aid in fighting off the dry air to its north..jmo..looks a little healthier the last few frames..
Member Since: September 27, 2007 Posts: 1 Comments: 22684

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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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