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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2571. catastropheadjuster
3:32 PM GMT on July 29, 2011
http://tampaspinsweather.webs.com/livecamfeedswchas e.htm

Some very pretty clouds and stuff.

Member Since: August 24, 2006 Posts: 21 Comments: 3648
2570. palmbaywhoo
3:28 PM GMT on July 29, 2011
Haha love it!

Quoting uptxcoast:


Arlen is a small town South of DFW probably down I-35 towards Austin. No rain for Arlen yet....

This fictional Town is right has severe drought conditions that is making Hank Crazy because he can't water his grass enough to due restrictions. Hank is furious because his lawn is starting to look like Bill's.

Dale is raking in the business as fire ants have been on the move as the drought continues.

Peggy as always is having issues with the low flow toilets that have been brought back due to the drought.

Boomhauer is mad because his chick magnet boat is high and dry in its boat slip and the lake is so low all the tree stumps are showing making any activity dangerous.

Propane sales are down as it is too hot to grill.

Drinking beer in the alley is only done in the early morning as Bill had heat stroke waving to cars on the highway. (Again)

The gang is riding out the drought by heading to the water park (Based on the very real water park Schlitterbahn and its Flowrider endless wave The Boogie Bahn)



Member Since: August 18, 2008 Posts: 0 Comments: 378
2569. tiggeriffic
3:28 PM GMT on July 29, 2011
Quoting TropicalAnalystwx13:
We used this for Earl last year...If it reaches 25N before 75W, it will likely recurve.

BUT, if it reaches 75W before it reaches 25N, it will likely make landfall in the southeast.


it also depends on the strength when it reaches those coordinates...i know you said most likely and those are key words but on sept 20-21 storm was at:
25.2 71.0 cat 2
26.3 72.2 cat 2
27.2 73.4 cat 3
28.0 74.9 cat 3

have noticed more so where it is when it rounds PR

Member Since: September 16, 2007 Posts: 0 Comments: 3599
2568. Vincent4989
3:27 PM GMT on July 29, 2011
NEW BLOG NEW BLOG NEW BLOG
Member Since: November 13, 2009 Posts: 2 Comments: 728
2567. FLWeatherFreak91
3:27 PM GMT on July 29, 2011
Areas from Brownsville into northern Mexico will receive a considerable amount of rain with this system while areas north of the circulation will observe heavier winds and considerably less rain than the southern quadrants of Don.

Member Since: December 1, 2006 Posts: 2 Comments: 3616
2566. ackee
3:25 PM GMT on July 29, 2011
Quoting jasonweatherman2011:
maybe more the models little more to the south
AGREE models intensify the system rather quickly looking at 91L current state THE longer it takes to devlop the further west and futher south it will track
Member Since: July 15, 2008 Posts: 0 Comments: 1341
2565. WeatherNerdPR
3:25 PM GMT on July 29, 2011
I think 91L is separating from the ITCZ.
Member Since: July 7, 2010 Posts: 0 Comments: 5519
2564. xcool
3:23 PM GMT on July 29, 2011
new blogggggg
Member Since: September 26, 2009 Posts: 2 Comments: 15603
2562. angiest
3:23 PM GMT on July 29, 2011
2555 - A few years ago we were eating at Luling City Meat Market in Houston, and there was someone at the bar area who sounded exactly like Dale.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
2561. Neapolitan
3:22 PM GMT on July 29, 2011
NEW BLOG ENTRY
Member Since: November 8, 2009 Posts: 4 Comments: 13258
2560. xcool
3:22 PM GMT on July 29, 2011
1005 AM EDT FRI 29 JULY 2011
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 30/1100Z TO 31/1100Z JULY 2011
TCPOD NUMBER.....11-059 AMENDMENT

I. ATLANTIC REQUIREMENTS
1. NEGATVIE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY:
A. INVEST SUSPECT AREA AT 31/1800Z NEAR 14.0N 54.0W.
Member Since: September 26, 2009 Posts: 2 Comments: 15603
2559. HurricaneDean07
3:22 PM GMT on July 29, 2011
TAWX Yep, 6 storms in July....
So far our July: 3 storms (but if Emily forms on sunday then we could squeeze out 4.)
Member Since: October 3, 2010 Posts: 40 Comments: 4129
2558. Hurricanejer95
3:21 PM GMT on July 29, 2011
2544

None of the other models show ex Don (when he becomes inland) touching my State, we had too much rain here !
Member Since: August 30, 2008 Posts: 1 Comments: 224
2556. xcool
3:21 PM GMT on July 29, 2011



0z ECM ensemble model
Member Since: September 26, 2009 Posts: 2 Comments: 15603
2555. uptxcoast
3:20 PM GMT on July 29, 2011
Quoting palmbaywhoo:
Where is Arlen Texas located? Will Hank's grass get some loving from ol Don?


Arlen is a small town South of DFW probably down I-35 towards Austin. No rain for Arlen yet....

This fictional Town is right has severe drought conditions that is making Hank Crazy because he can't water his grass enough to due restrictions. Hank is furious because his lawn is starting to look like Bill's.

Dale is raking in the business as fire ants have been on the move as the drought continues.

Peggy as always is having issues with the low flow toilets that have been brought back due to the drought.

Boomhauer is mad because his chick magnet boat is high and dry in its boat slip and the lake is so low all the tree stumps are showing making any activity dangerous.

Propane sales are down as it is too hot to grill.

Drinking beer in the alley is only done in the early morning as Bill had heat stroke waving to cars on the highway. (Again)

The gang is riding out the drought by heading to the water park (Based on the very real water park Schlitterbahn and its Flowrider endless wave The Boogie Bahn)



Member Since: September 23, 2005 Posts: 6 Comments: 233
2554. smitty1791
3:20 PM GMT on July 29, 2011
Quoting oreodogsghost:
Nice rain in downtown Houston. Looks like we are in for a wet day.


Its pouring in Friendswood as well. Got alot of rain yesterday
img src="Photobucket">
Member Since: July 27, 2011 Posts: 0 Comments: 13
2553. IceCoast
3:20 PM GMT on July 29, 2011
Model consensus is strong for a typhoon affecting japan islands/taiwan/china in the long range. Pretty scary scenario with storm moving north towards the islands then getting pushes back west towards china. Ma-on thankfully failed to do what was forecasted, let's see what tropical storm Muifa decides to do.

GFS brings it dangerously close to Shanghai, moving NW.


Euro much farther south bringing it very close to Taipei, Taiwan and then into the China coast.


Member Since: October 17, 2010 Posts: 0 Comments: 1267
2551. NASA101
3:19 PM GMT on July 29, 2011
91L looks very ragged at the moment...still ways to go before a TD classification!
My take is that models are overdoing the intensity in the short term!
Member Since: August 16, 2007 Posts: 0 Comments: 276
2550. GeoffreyWPB
3:18 PM GMT on July 29, 2011
I'm thinking that if 91L keeps up its progress, Recon will find at least a TD on Sunday.
Member Since: September 10, 2007 Posts: 0 Comments: 10577
2549. HCW
3:17 PM GMT on July 29, 2011
Quoting angiest:
Do I see the center of Don trying to move into very long range Brownsville radar?


Sure looks like it. Lots of lightning with Don also

Link
Member Since: August 10, 2002 Posts: 0 Comments: 1346
2548. tiggeriffic
3:17 PM GMT on July 29, 2011
Hurricane Hugo went from TD to TS to hurricane in 3 days...TD to TS over night...anything is possible
Member Since: September 16, 2007 Posts: 0 Comments: 3599
2547. TropicalAnalystwx13
3:17 PM GMT on July 29, 2011
Quoting EcoLogic:
I would be interested in a 2011 / 2005 comparison. If we get Emily in the next two days, we are tied, right? Are we set up to get into the Greek alphabet again, or are conditions not going to produce that many TC's?


No, 2005 was already on the "G" storm.
Member Since: July 6, 2010 Posts: 108 Comments: 30241
2546. SLU
3:17 PM GMT on July 29, 2011
Inconclusive

Member Since: July 13, 2006 Posts: 12 Comments: 4731
2545. angiest
3:16 PM GMT on July 29, 2011
Do I see the center of Don trying to move into very long range Brownsville radar?
Member Since: August 26, 2006 Posts: 16 Comments: 4766
2543. EcoLogic
3:16 PM GMT on July 29, 2011
I would be interested in a 2011 / 2005 comparison. If we get Emily in the next two days, we are tied, right? Are we set up to get into the Greek alphabet again, or are conditions not going to produce that many TC's?
Member Since: June 29, 2010 Posts: 0 Comments: 53
2542. nigel20
3:15 PM GMT on July 29, 2011
I don't think 91l will curve out to sea
Member Since: November 6, 2010 Posts: 9 Comments: 7435
2541. ackee
3:15 PM GMT on July 29, 2011
Quoting TropicalAnalystwx13:
How about a serious, and not too far out poll?

Q: When will 91L develop into TD #5/Emily?

A. Today
B. Tomorrow
C. Sunday
D. Monday/later

I choose C. - Sunday.
D
Member Since: July 15, 2008 Posts: 0 Comments: 1341
2540. islander101010
3:15 PM GMT on July 29, 2011
hard for my eyes to see the difference between the orange and red of nhc
Member Since: September 11, 2010 Posts: 0 Comments: 4017
2538. Hurricanejer95
3:14 PM GMT on July 29, 2011
Quoting NotCircumventing:
2518 ..

I don't have those fixes, but I can only assume that the XTRP (not a) Model shows a landfall near ... dare I say it ... Matagorda, TX.

Or so.

XTRP shows (ex)Don passing by the Bay Area :-O
Member Since: August 30, 2008 Posts: 1 Comments: 224
2533. ProgressivePulse
3:11 PM GMT on July 29, 2011
Quoting tennisgirl08:
91L will become Emily...sooner rather than later...but it is absolutely ridiculous to over exaggerate the effects she will have on the CONUS. It's a wait and see game. No need to freak out, just yet.


Public blog. However ridiculous it is, it's there, it's always there and needs to be dealt with. However, 91L should be paid close attention to. Locals is SEFL are mentioning it in their long range forecasts as being at 75W in 8 days.
Member Since: August 19, 2005 Posts: 5 Comments: 4863
2532. ncstorm
3:11 PM GMT on July 29, 2011
91L
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)


Dynamic Models (More sophisticated models)
Member Since: August 19, 2006 Posts: 13 Comments: 13434
2531. GeoffreyWPB
3:10 PM GMT on July 29, 2011
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1005 AM EDT FRI 29 JULY 2011
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 30/1100Z TO 31/1100Z JULY 2011
TCPOD NUMBER.....11-059 AMENDMENT

I. ATLANTIC REQUIREMENTS
1. NEGATVIE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY:
A. INVEST SUSPECT AREA AT 31/1800Z NEAR 14.0N 54.0W.
B. ADDED....A G-IV MISSION FOR 01/0000Z.
3. REMARK: P-3 MISSIONS FOR 29/1200Z AND 30/0000Z
CANCELED BY NHC AT 28/2345Z.
Member Since: September 10, 2007 Posts: 0 Comments: 10577
2530. KaNaPaPiJoSa
3:10 PM GMT on July 29, 2011
Quoting TropicalAnalystwx13:
How about a serious, and not too far out poll?

Q: When will 91L develop into TD #5/Emily?

A. Today
B. Tomorrow
C. Sunday
D. Monday/later

I choose C. - Sunday.


Forecasting the forecast...LOL, I love it.
Member Since: June 14, 2010 Posts: 0 Comments: 57
2529. jpsb
3:09 PM GMT on July 29, 2011
Quoting NotCircumventing:
2447 ...

Migth still make it to Matagorda. Or so.

Seriously, I know I have said it a lot, but it is still a player with over 12 hours til landfall remaining.

Especially with this right-bias we see.
Figures crossed for matagorda, but if Dons get strong west again, weak north west so I am hoping he stays weak.
Member Since: June 30, 2009 Posts: 0 Comments: 1010
2528. angiest
3:09 PM GMT on July 29, 2011
Quoting NotCircumventing:
2518 ..

I don't have those fixes, but I can only assume that the XTRP (not a) Model shows a landfall near ... dare I say it ... Matagorda, TX.

Or so.



Port Lavaca-ish.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
2525. taco2me61
3:08 PM GMT on July 29, 2011
Quoting TropicalAnalystwx13:
We used this for Earl last year...If it reaches 25N before 75W, it will likely recurve.

BUT, if it reaches 75W before it reaches 25N, it will likely make landfall in the southeast.


Too soon to say I'm not going out on that limb just yet if you know what I'm saying :o)

Taco :o)
Member Since: July 7, 2005 Posts: 6 Comments: 3166
2524. TropicalAnalystwx13
3:08 PM GMT on July 29, 2011
How about a serious, and not too far out poll?

Q: When will 91L develop into TD #5/Emily?

A. Today
B. Tomorrow
C. Sunday
D. Monday/later

I choose C. - Sunday.
Member Since: July 6, 2010 Posts: 108 Comments: 30241
2523. TropicalAnalystwx13
3:05 PM GMT on July 29, 2011
We used this for Earl last year...If it reaches 25N before 75W, it will likely recurve.

BUT, if it reaches 75W before it reaches 25N, it will likely make landfall in the southeast.
Member Since: July 6, 2010 Posts: 108 Comments: 30241
2522. Ameister12
3:05 PM GMT on July 29, 2011
91L floater is up!
Member Since: August 9, 2009 Posts: 10 Comments: 4498
2521. HurricaneDean07
3:04 PM GMT on July 29, 2011
quakeman, tell Cantore he needs to move farther north, cuase Don isnt hitting there(the rain will) but landfall closer to corpus christi
Member Since: October 3, 2010 Posts: 40 Comments: 4129

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About JeffMasters

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