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

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2005 Hurricanes Atlantic
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Hurricanes Western Pacific 2011
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Tropical Storms Atlantic 2005
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I'll have a new post Friday morning.

Jeff Masters

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Time: 23:36:00Z
Coordinates: 24.4667N 91.7667W
Acft. Static Air Press: 753.0 mb (~ 22.24 inHg)
Acft. Geopotential Hgt: 2,507 meters (~ 8,225 feet)
Extrap. Sfc. Press: 997.1 mb (~ 29.44 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 121° at 27 knots (From the ESE at ~ 31.0 mph)
Air Temp: 21.8°C (~ 71.2°F)
Dew Pt: 8.9°C (~ 48.0°F)
Peak (10s) Flt. Lvl. Wind: 31 knots (~ 35.6 mph)
SFMR Peak (10s) Sfc. Wind: 31 knots (~ 35.6 mph)
SFMR Rain Rate: 0 mm/hr (~ 0 in/hr)
(*) Denotes suspect data
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Dare I say rapid intensification?
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Quoting Patrap:
Dvorak



Pat that is crazy, are those just overshooting clouds or is this trying to form an eyewall?
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I don't think Kermit's data is too reliable.

I'd wait for the WC-130J to penetrate the circulation in a few minutes to know what the pressure really is.

A pressure of 996mb would not be too surprising though.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
767. yoboi
we should call the NHC and tell them what a great job they are doing....
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Quoting CybrTeddy:
Recon just found pressures of 996.1 mb and SFMR winds of 58 knots.



DON is makeing a run for hurricane
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Dvorak

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Recon just found pressures of 996.1 mb and SFMR winds of 58 knots.
Member Since: July 8, 2005 Posts: 259 Comments: 24021
Quoting Tazmanian:



they this found a mb of 996

996.1 mb
(~ 29.41 inHg)


I know Taz, looks like it may actually make a run at a Hurricane. I better get my plate of crow from earlier.
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Quoting MrstormX:
Wow.....

000
URNT15 KWBC 282344
NOAA2 0304A DON HDOB 23 20110728
233430 2422N 09143W 7507 02528 0003 175 137 219027 030 055 012 03
233500 2424N 09144W 7540 02490 9961 224 095 175020 021 058 013 03
233530 2426N 09145W 7517 02514 9961 222 088 143029 031 032 001 00
233600 2428N 09146W 7530 02507 9971 218 089 121027 031 031 000 00
233630 2430N 09146W 7526 02515 9996 197 097 093032 034 036 002 00

233700 2432N 09147W 7527 02519 0004 194 099 077038 039 038 000 00
233730 2434N 09148W 7531 02519 0015 187 102 071035 036 035 000 00
233800 2436N 09149W 7529 02525 0020 187 100 077035 036 033 000 00
233830 2438N 09150W 7529 02526 0034 173 110 081034 035 /// /// 03
233900 2439N 09149W 7531 02527 0040 171 112 083033 034 /// /// 03
233930 2440N 09147W 7527 02531 0039 172 111 087032 033 034 000 00
234000 2440N 09145W 7530 02527 0035 174 109 091033 034 034 002 00
234030 2441N 09143W 7532 02526 0034 177 107 103034 036 034 000 00
234100 2441N 09141W 7532 02526 0038 173 108 107035 036 035 001 00
234130 2442N 09140W 7528 02533 0044 168 111 108036 036 035 000 00
234200 2442N 09138W 7528 02531 0042 170 110 111034 035 037 001 00
234230 2443N 09136W 7530 02534 0046 169 110 119034 036 038 001 00
234300 2443N 09134W 7530 02533 0048 168 110 130036 037 037 001 00
234330 2444N 09132W 7530 02536 0051 167 111 132034 035 037 000 00
234400 2444N 09130W 7528 02540 0057 162 112 130034 034 037 000 00





yup wish one of you guys made DON mad
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Quoting HurricaneHunterJoe:
Explain that sat loop in layman terms please.


Its a Hi Rez View ,,or what you'd see with your eye from Orbit
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Guys!!!!!! we have a strong ts maybe minimal hurricane making landfall in texas if emily forms we will have 5 named storms in late july early august similar to 08. i think csu will up there predictions :)
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Quoting gtownTX:
Come on Don!!!! To heck with grass, it's the trees I'm sad for. Here in Central Tx., I've already lost some small trees in my yard and the medium sized ones are in maximum stress from 3 years of drought. Can't provide enough water from a sprinkler to offset this intense dry heat.

On the flip side, if you are a tree trimmer, this Fall and winter would be max earnings for anyone coming to this area as branches and whole trees will need removing. There are dead trees all through the neighborhood.

Same thing with trees in the College Station area! I went to the Woodlands last weekend and there are a bunch of dead trees down there too. We need the rain so bad!
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Wow.....

000
URNT15 KWBC 282344
NOAA2 0304A DON HDOB 23 20110728
233430 2422N 09143W 7507 02528 0003 175 137 219027 030 055 012 03
233500 2424N 09144W 7540 02490 9961 224 095 175020 021 058 013 03
233530 2426N 09145W 7517 02514 9961 222 088 143029 031 032 001 00
233600 2428N 09146W 7530 02507 9971 218 089 121027 031 031 000 00
233630 2430N 09146W 7526 02515 9996 197 097 093032 034 036 002 00

233700 2432N 09147W 7527 02519 0004 194 099 077038 039 038 000 00
233730 2434N 09148W 7531 02519 0015 187 102 071035 036 035 000 00
233800 2436N 09149W 7529 02525 0020 187 100 077035 036 033 000 00
233830 2438N 09150W 7529 02526 0034 173 110 081034 035 /// /// 03
233900 2439N 09149W 7531 02527 0040 171 112 083033 034 /// /// 03
233930 2440N 09147W 7527 02531 0039 172 111 087032 033 034 000 00
234000 2440N 09145W 7530 02527 0035 174 109 091033 034 034 002 00
234030 2441N 09143W 7532 02526 0034 177 107 103034 036 034 000 00
234100 2441N 09141W 7532 02526 0038 173 108 107035 036 035 001 00
234130 2442N 09140W 7528 02533 0044 168 111 108036 036 035 000 00
234200 2442N 09138W 7528 02531 0042 170 110 111034 035 037 001 00
234230 2443N 09136W 7530 02534 0046 169 110 119034 036 038 001 00
234300 2443N 09134W 7530 02533 0048 168 110 130036 037 037 001 00
234330 2444N 09132W 7530 02536 0051 167 111 132034 035 037 000 00
234400 2444N 09130W 7528 02540 0057 162 112 130034 034 037 000 00

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the NHC , may want too take back about the hurricane thing i think this thing is well under way
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Quoting MiamiHurricanes09:
In 5 days the CATL wave should be in close proximity to the Lesser Antilles (likely to the west of them).

What I was discussing was a whole different system that is being developed by the models that seems to originate from the monsoonal trough in the southwestern Caribbean.


Hmm, haven't had a look at the GFS in a couple of days, I must check it out.
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Anybody have a link handy for the steering layers?
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Quoting Tazmanian:
crap DON going under a RI

Proof please?
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753. TI882
Don is approaching south side of old loop current.
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Quoting weatherh98:
half an eyewall???? that isnt 45


Just waiting for more data , I think Don is a 60-65mph TS atm.
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Quoting MrstormX:


Pressure falling



they this found a mb of 996

996.1 mb
(~ 29.41 inHg)
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crap DON going under a RI
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Quoting JLPR2:


So far the models send it to the central Lesser Antilles, (north of Barbados) or to the NE Caribbean. (US Virgin Islands.)
But none the less all the people form the islands chain should keep an eye on it.


Thanks guys, just as I thought.........I will continue to watch. Barbados has Carnival this week'n with Carnival Jump in the street on Monday,,,should be interesting!
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Quoting NICycloneChaser:


Surely the tropical wave won't be far from the western Caribbean in 5 days?
In 5 days the CATL wave should be in close proximity to the Lesser Antilles (likely to the west of them).

What I was discussing was a whole different system that is being developed by the models that seems to originate from the monsoonal trough in the southwestern Caribbean.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting stormpetrol:
ime: 23:34:00Z
Coordinates: 24.3333N 91.7167W
Acft. Static Air Press: 752.6 mb (~ 22.22 inHg)
Acft. Geopotential Hgt: 2,512 meters (~ 8,241 feet)
Extrap. Sfc. Press: 1003.2 mb (~ 29.62 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 242° at 23 knots (From the WSW at ~ 26.4 mph)
Air Temp: 15.0°C (~ 59.0°F)
Dew Pt: 13.8°C (~ 56.8°F)
Peak (10s) Flt. Lvl. Wind: 27 knots (~ 31.0 mph)
SFMR Peak (10s) Sfc. Wind: 44 knots (~ 50.6 mph)
SFMR Rain Rate: 2 mm/hr (~ 0.08 in/hr)


Pressure falling
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996 mb
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ime: 23:34:00Z
Coordinates: 24.3333N 91.7167W
Acft. Static Air Press: 752.6 mb (~ 22.22 inHg)
Acft. Geopotential Hgt: 2,512 meters (~ 8,241 feet)
Extrap. Sfc. Press: 1003.2 mb (~ 29.62 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 242° at 23 knots (From the WSW at ~ 26.4 mph)
Air Temp: 15.0°C (~ 59.0°F)
Dew Pt: 13.8°C (~ 56.8°F)
Peak (10s) Flt. Lvl. Wind: 27 knots (~ 31.0 mph)
SFMR Peak (10s) Sfc. Wind: 44 knots (~ 50.6 mph)
SFMR Rain Rate: 2 mm/hr (~ 0.08 in/hr)
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04L/TS/D/CX
ON APPROACH
IR NIGHT VIEW


Member Since: July 15, 2006 Posts: 171 Comments: 53838
Lol. I have no manners. Good evening all. Looks like Don listened and is getting his act together. Just hope not too together. And hope he rains where needed. Now 91l to be got the crayon. I'm soo behind! So everything's normal. :)
Member Since: August 24, 2010 Posts: 0 Comments: 151
741. yoboi
Quoting floridaboy14:
Guys its moving WNW not NW anymore interesting


heading toward lower texas NHC has been dead on with this storm....
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Ts Don Update With Video
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Quoting MiamiHurricanes09:
Another area to watch in the next 5 days is the western Caribbean/BOC as indicated by the GFS. The ECMWF and CMC show a disturbance in the region, but don't develop it into a tropical cyclone.


Surely the tropical wave won't be far from the western Caribbean in 5 days?
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Hey all. It sure has been awhile(Since Ike maybe?) I haven't chatted or provided any analysis in a long time. Well Don is sure trying to defy the models, isn't he? That northerly shear looks to be weakening some per viewing several loops. Also I like seeing the cirrus beginning to fan out on all sides, Don's exhaust system kicking in. It appears he is growing up before our very eyes!
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737. DVG
Quoting stormpetrol:
Looks like Don starting to build an eyewall 24.7N/92W


The dvorak seems to agree with you.
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Quoting Patrap:
Enhanced Infrared (IR) Imagery (4 km Mercator)

whats that big concave looking ring on top?
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How is DON still 45mph?
How is DON moving WNW?
Is DON really heading for Texas?
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Quoting CybrTeddy:
Here we go again.. 20% on the CATL wave. I expect 91L soon. The last half of July has been really active, a lot more so than the lat half of 2008's July was and in a downward MJO phase, and here we are talking about the possibility of our 5th system.
Another area to watch in the next 5 days is the western Caribbean/BOC as indicated by the GFS. The ECMWF and CMC show a disturbance in the region, but don't develop it into a tropical cyclone.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
733. jpsb
Quoting floridaboy14:
Guys its moving WNW not NW anymore interesting
Yeah as soon as I said matagorda bay to galveston bay it changed direction :(
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Quoting floridaboy14:
Guys its moving WNW not NW anymore interesting


The models took a rather large southward shift this evening. Looking more like a south Texas landfall to me.
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23:15 UTC Rainbow

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Quoting Patrap:
ESL by LSU GOES-13 Low Cloud Product Loop
Explain that sat loop in layman terms please.
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Quoting bohonkweatherman:
Good for you Ark, you are as hot as Texas, today was my 50th day of 100 or greater, 63 days for San Angelo. I think 2011 will go down as hottest year ever, records being broken all time for streaks and hottest temperatures ever.


I'm glad for Ark. too. And I hope the wet stuff visits you soon! :)
Member Since: August 24, 2010 Posts: 0 Comments: 151
Quoting MiamiHurricanes09:
Tropical wave in the CATL upgraded to 20%. Expect 91L soon.


Looks like we may just see Emily before July is out.
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half an eyewall???? that isnt 45
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726. JLPR2
Quoting weatherh98:


close but mo cigar look at the guy above


look at 707 haha

But we don't have a yellow circle on the map yet.
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Guys its moving WNW not NW anymore interesting
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Quoting weatherh98:


any data yet....
Mission number 3 is at the center presure has dropped 1mb and wind speeed in the eye wall is 50mph
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Here we go again.. 20% on the CATL wave. I expect 91L soon. The last half of July has been really active, a lot more so than the lat half of 2008's July was and in a downward MJO phase, and here we are talking about the possibility of our 5th system.
Member Since: July 8, 2005 Posts: 259 Comments: 24021
Come on Don!!!! To heck with grass, it's the trees I'm sad for. Here in Central Tx., I've already lost some small trees in my yard and the medium sized ones are in maximum stress from 3 years of drought. Can't provide enough water from a sprinkler to offset this intense dry heat.

On the flip side, if you are a tree trimmer, this Fall and winter would be max earnings for anyone coming to this area as branches and whole trees will need removing. There are dead trees all through the neighborhood.
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Enhanced Infrared (IR) Imagery (4 km Mercator)

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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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