Don battling dry air and wind shear

By: Dr. Jeff Masters , 7:37 PM GMT on July 28, 2011

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Tropical Storm Don continues to be an unimpressive low-end tropical storm as it continues northwest towards the Texas coast. Don formed yesterday afternoon from an African tropical wave that moved into the Gulf of Mexico under a region of low wind shear. Don's formation date of July 27 is nearly a month ahead of the usual August 23 date for the arrival of the season's fourth named storm of the year. There is currently no hurricane hunter airplane in Don, and a new airplane is not due in the storm until tonight. The last center fix at 1pm EDT found surface winds of 45 mph and a central pressure of 1005 mb, a 4 mb rise from earlier this morning. 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 5 - 15 knots of shear from strong upper level winds out of the north. This shear is creating problems for Don by injecting dry air into the system. Visible satellite imagery from early this afternoon showed the presence of surface arc-shaped clouds expanding outwards to the north from the center of Don. These type of clouds are a sign that the storm is struggling with dry air. When dry air at middle levels of the atmosphere gets injected into thunderstorms due to wind shear, the dry air tends to create strong downdrafts that rob the storm of moisture. These downdrafts spread out at the ocean surface and create arc-shaped surface cumulus clouds.


Figure 1. Visible satellite image of Don from pm EDT July 28, 2011, showing arc-shaped surface clouds--the tell-tale sign of dry air interfering with the storm's organization.


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 bring significant rains to Texas? According to the National Climatic Data Center, the six-month period ending in June 2011 was the driest on record. Average rain between January and June was more than eight inches (203 millimeters) below average in Texas, and the state experienced record heat between April and June. The heat and lack of rain have brought exceptional drought--the highest category of drought--to over 75% of the state. 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. We don't 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. Don's small size makes it prone to dry air and wind shear, though, and it is uncertain whether the storm can overcome these problems enough to become a significant rain maker. NHC gave Don a 12% chance of intensifying into a hurricane in the 11am advisory, which is a reasonable forecast, since Don is running out of time to get its act together in time to become a hurricane. None of the computer models is predicting Don will become a hurricane.

For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast. The 11 am version of this forecast shows that Port O'Connor, Texas has the highest chance of tropical storm-force winds (39+ mph): 45%.

New hurricane archive search feature
The autocomplete entities in the wunderground search box has been extended to include hurricanes, so you can now search for a storm by name, year, or basin. Here are some examples in case you feel like exploring your new options:

By name:

Hurricane David - Atlantic, 1979
David, Major Hurricane - Atlantic, 1979
Major Hurricane David - Atlantic, 1979

By year:

2005 Hurricanes Atlantic
2007 Hurricanes Eastern Pacific

By basin:

Hurricanes Western Pacific 2011
Hurricanes Atlantic 2008

By category:

Tropical Storms Atlantic 2005
Tropical Depressions Indian Ocean 2011
Subtropical Storms Eastern Pacific 2010
Extratropical Storms Western Pacific 1988

I'll have a new post Friday morning.

Jeff Masters

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Quoting stormpetrol:
Time: 21:53:00Z
Coordinates: 24.2333N 91.3833W
Acft. Static Air Press: 751.7 mb* (~ 22.20 inHg*)
Acft. Geopotential Hgt: 2,533 meters* (~ 8,310 feet*)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 211° at 4 knots (From the SSW at ~ 4.6 mph)
Air Temp: 14.1°C* (~ 57.4°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 6 knots (~ 6.9 mph)
SFMR Peak (10s) Sfc. Wind: 63 knots (~ 72.4 mph)
SFMR Rain Rate: 37 mm/hr (~ 1.46 in/hr)

What's this?

no way??? almost a hurricane? hhaha
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Floater - Rainbow Color Infrared Loop

Zoom,Boxes,and Tropical Points active
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Don continues to organize nicely. Intense thunderstorms continue to blow up over the center:

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Quoting Max1023:
unflagged 50 knot sfmr winds with only 20kt flight level- apparently Don is stronger at the surface.
Nope, that would indicate that the surface winds are contaminated/SFMR instrument isn't operating properly.

I doubt that Don is anything more than a 50-55mph tropical storm (yes, I know they don't use 55mph anymore).
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Is it me or does it look like Don is heading to mexico?
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Time: 21:53:00Z
Coordinates: 24.2333N 91.3833W
Acft. Static Air Press: 751.7 mb* (~ 22.20 inHg*)
Acft. Geopotential Hgt: 2,533 meters* (~ 8,310 feet*)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 211° at 4 knots (From the SSW at ~ 4.6 mph)
Air Temp: 14.1°C* (~ 57.4°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 6 knots (~ 6.9 mph)
SFMR Peak (10s) Sfc. Wind: 63 knots (~ 72.4 mph)
SFMR Rain Rate: 37 mm/hr (~ 1.46 in/hr)

What's this?
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Quoting MrstormX:
Wow the NOAA Hurricane Hunters are finding different results then their AF Predecessors were.


what are they finding?

sheri
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Just noticed this data wasn't flagged as corrupt:

Time: 21:53:00Z
Coordinates: 24.2333N 91.3833W
Acft. Static Air Press: 751.7 mb* (~ 22.20 inHg*)
Acft. Geopotential Hgt: 2,533 meters* (~ 8,310 feet*)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 211° at 4 knots (From the SSW at ~ 4.6 mph)
Air Temp: 14.1°C* (~ 57.4°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 6 knots (~ 6.9 mph)
SFMR Peak (10s) Sfc. Wind: 63 knots (~ 72.4 mph)
SFMR Rain Rate: 37 mm/hr (~ 1.46 in/hr)
(*) Denotes suspect data



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unflagged 50 knot sfmr winds with only 20kt flight level- apparently Don is stronger at the surface.
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hopefully things dont too out of hand
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Quoting tiggeriffic:


exactly...how can one who is trying to be officious be guilty of the same sin?


Is that a riddle?
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Hey Flood...Don has blown u a script
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Quoting Floodman:


Been lurking a wee bit; I'm actually finally caught up on work and feel like a good fight...I come in here and the only person being "officious" is Taz, and I like Taz...this place is no fun anymore. Where have all the good trolls gone?


Too bad we don't have a like button...
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what do you think the chances that Don will continue to strengthen without waning any?
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The wave in the central Atlantic is the one I'm more worried about.
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400. DFWjc
Quoting belizeit:
HH is reporting heavy rains of 2in per hr with a susspect wind reading of 72mph


Ok, my head now officially hurts, so it is strengthening and moving WNW???
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Don't hit mexico, baby! Hit Rodeo State!
Member Since: November 13, 2009 Posts: 2 Comments: 728
Wow the NOAA Hurricane Hunters are finding different results then their AF Predecessors were.
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HH is reporting heavy rains of 2in per hr with a susspect wind reading of 72mph
Member Since: January 10, 2010 Posts: 0 Comments: 917
Quoting VAbeachhurricanes:


Officious means bossy tigger haha


exactly...how can one who is trying to be officious be guilty of the same sin?
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52 knots
(~ 59.8 mph)

51 knots
(~ 58.6 mph)

50 knots
(~ 57.5 mph)

47 knots
(~ 54.0 mph)
Member Since: July 8, 2005 Posts: 259 Comments: 23496
Quoting CybrTeddy:
SFMR
57 knots
(~ 65.5 mph)
4.5 more mph and we have a hurricane thunderstorm
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392. xcool
cat 1 come soon -don - jmo
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Quoting CybrTeddy:
SFMR
57 knots
(~ 65.5 mph)


Nice...they probably won't go with that intensity, but the center appears to be right under that big blowup of convection. Don is a lot better organized than earlier. However, his trend has been to wax and wane. He actually needs to maintain this structure for a while.
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Quoting CybrTeddy:
SFMR
57 knots
(~ 65.5 mph)

Really?
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Quoting nigel20:
AThanks for the info it was very informative
no problem
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what in the heck is causing the slight westward movement i don't remember that being forecasted is there anything else that they didnt tell us?
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Quoting Floodman:


Been lurking a wee bit; I'm actually finally caught up on work and feel like a good fight...I come in here and the only person being "officious" is Taz, and I like Taz...this place is no fun anymore. Where have all the good trolls gone?


Hey just thought I would say Hi, I'm glad someone was working. What cha think about the wave way out theeeerrreee? There's alot of folks missing that use to be here, I asked about u a couple of weeks ago. Glad to see ya.

sheri
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Don has covered 3/4 of it's circulation, with 1/4 being naked. But he could solve it with the convection to the NE.
Member Since: November 13, 2009 Posts: 2 Comments: 728
SFMR
57 knots
(~ 65.5 mph)
Member Since: July 8, 2005 Posts: 259 Comments: 23496
Quoting tiggeriffic:


officious? really? you must have missed it when he posted that Dr Masters needed to go back on Vacation so the storms would come back...but hey...who am i to judge...but just so I make sure I stay officious and on topic mind you...i see the the potential for Don to get stronger than what is predicted...he is doing what he wants so far against all models...


Officious means bossy tigger haha
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Quoting GHOSTY1:
who stills feel a corpus christi or rockport landfall is gonna happen?
I agree with CCTX as landfall still. See no reason yet to think otherwise.
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i guess that cloudburst left cause of me, i never intended to make him so excited, i respect everyones opinion and just wanted to display my own. and sorry if i misquote someone i don't intend on it.
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Quoting tiggeriffic:


lol tired of people trolling...one says this another that then people make threats when they are just as guilty for making comments that are not topic related...over it...been lurking more than posting today...how bout you Flood?


Tig, you have WUMail, you bouncy thing you
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Quoting GHOSTY1:
who stills feel a corpus christi or rockport landfall is gonna happen?



%12 ch if this storm dos not turn soon it will head in too MX
Member Since: May 21, 2006 Posts: 5091 Comments: 114649
Quoting Floodman:


Been lurking a wee bit; I'm actually finally caught up on work and feel like a good fight...I come in here and the only person being "officious" is Taz, and I like Taz...this place is no fun anymore. Where have all the good trolls gone?


officious? really? you must have missed it when he posted that Dr Masters needed to go back on Vacation so the storms would come back...but hey...who am i to judge...but just so I make sure I stay officious and on topic mind you...i see the the potential for Don to get stronger than what is predicted...he is doing what he wants so far against all models...
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375. DFWjc
Quoting GHOSTY1:
who stills feel a corpus christi or rockport landfall is gonna happen?


I'm still going with Aransas Pass...
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Quoting MississippiWx:
Winds are still coming out of the SSE closer to the middle of the convection:



can you please tell me where i can get satellite data for google earth?
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who stills feel a corpus christi or rockport landfall is gonna happen?
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Winds are still coming out of the SSE closer to the middle of the convection:



Edit: Center found it looks like....right where the newest blowup of convection is ongoing.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.