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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What will Don peak at?
A.45-50 mph
B.60-65 mph
C.70 mph
D.Cat. 1
E.Cat. 2
F.Cat. 3
G.Cat. 4
H.Cat. 5
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Anticyclone associated with Don.
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Quoting ProgressivePulse:



That's the plan, spin out right in the middle of the state would be perfect. However, like FL's situation, ya gotta back that up with some regular rainfall or it ends up being for nuttin.

I'm hoping Texas gets more rain after this.
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1116. Walnut
Quoting ProgressivePulse:



That's the plan, spin out right in the middle of the state would be perfect. However, like FL's situation, ya gotta back that up with some regular rainfall or it ends up being for nuttin.
Here in San Antonio, the forecast post-Don is for temps above 100 all next week. The rain will help some to fill aquifers and alleviate some drought, but it will be August and the only precip we get will be from rare Sea Fronts and tropical systems.
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For those who weren't here, here's my first blog.
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lets pray don gets further north. texas DESPERATLY needs that rain
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August will be insane and september
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1112. Patrap
Quoting floridaboy14:
Just curious. are the hurricane hunters still in don and do they plan on going into don tomorrow and if so when?




Look on the left side of the NHC page and you will see Aircraft RECON


Plan of the Day

000
NOUS42 KNHC 281445
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1045 AM EDT THU 28 JULY 2011
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 29/1100Z TO 30/1100Z JULY 2011
TCPOD NUMBER.....11-058

I. ATLANTIC REQUIREMENTS
1. TROPICAL STORM DON
FLIGHT ONE - TEAL 73 FLIGHT TWO - NOAA 42
A. 29/1200,1800Z A. 30/0000Z
B. AFXXX 0604A DON B. NOAA2 0704A DON
C. 29/1015Z C. 29/2000Z
D. 26.1N 93.8W D. 27.3N 96.0W
E. 29/1130Z TO 29/1800Z E. 29/2230Z TO 30/0230Z
F. SFC TO 15,000 FT F. SFC TO 15,000 FT

FLIGHT THREE - TEAL 74
A. 30/0000,0600Z
B. AFXXX 0804A DON
C. 29/2200Z
D. 27.3N 96.0W
E. 29/2330Z TO 30/0600Z
F. SFC TO 15,000 FT

2. OUTLOOK FOR SUCCEEDING DAY: POSSIBLE 30/1200 FIX.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.
JWP

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Quoting floridaboy14:
Just curious. are the hurricane hunters still in don and do they plan on going into don tomorrow and if so when?


Link
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Quoting TropicalAnalystwx13:


Where the heck did that come from?


It started forming this afternoon. Maps didn't show it but, the clouds did.
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Don has really flared up......new yellow circle on the map
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Quoting floridaboy14:
Just curious. are the hurricane hunters still in don and do they plan on going into don tomorrow and if so when?

They are flying into the storm three times tomorrow...And yes, they are still in Don. They are currently measuring the wind field.
Member Since: July 6, 2010 Posts: 113 Comments: 32262
Quoting Chicklit:

Yeah, we're all rooting for goofy Don to smack Texas with a bunch of rain.



That's the plan, spin out right in the middle of the state would be perfect. However, like FL's situation, ya gotta back that up with some regular rainfall or it ends up being for nuttin.
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Quoting ProgressivePulse:
Nice little ULAC slightly displaced over DON.



Where the heck did that come from?
Member Since: July 6, 2010 Posts: 113 Comments: 32262
Just curious. are the hurricane hunters still in don and do they plan on going into don tomorrow and if so when?
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My bad about saying an Invest.....its not an Invest yet but, i am sure it will be shortly. SORRY
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Quoting Dirtleg:
Someone tell Oz not to park on the beach this time!!!


I emailed him what you said. I agree. His FB post makes me think he is going to stay in the greater CC area because of the 4G network.
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Here is my advice for new members. Although I may not be the most popular poster here I have been around for a long time on here. Here are a few things to keep in mind for your first tropical season as a member here:

1. Give your opinion on tropical storms with backup... find specific data to back up your forecasters.

2. Ask questions.. even if you are the lead forecaster at National Hurricane Center... ask questions to show your genuine interest in other peoples opinions.

3. Stand up for yourself but don't resort to personal attacks.... defend your forecast don't put down your "opponent"

4. Read.... Read.... Read.... Read.... Read... find out what other people are saying don't try to control the conversation at all times.

5. Admit when you are wrong... if you mess up badly on a forecast... find out why and explain where you messed up... this will show that you are human just like the rest of us.

6. Be humble when you are right. Even if you got your forecast 100% right compliment someone else who also got the forecast right or don't say anything about your own forecast.

7. Post on other blogs in the same matter to help increase your post count and your reputation on the board.

8. Write your own blogs about the tropical system.. and keep it updated even if no one comments (many people read them even if no one comments)

9. Don't post links to your own website on here (you will be gone before you can create any reputation).

10. And finally... don't let people get on your nerves... there will always be bickering but you don't have to be a part of it.


Thanks for reading this post of mine
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Quoting lucreto:
NHC will probably terminate all warnings (except maybe the Mouth of Rio Grande to Port Mansfield watch) at the 11pm advisory.


No, the nhc will continue the warnings to save people's lives. I know you try to get attention by saying the opposite of what is going to happen, but it gets old. Sorry.

So if Don experiences RI, that would put him in a different steering level? Would he track more N or S?
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Quoting floridaboy14:
what will be the next advisory at 11pm for don?
a: 45
b: 50
c: 55-60
d:65
e: 70 im going with B

C.
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Nice little ULAC slightly displaced over DON.

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Quoting stormpetrol:
I said last night Don would be a hurricane at landfall, i'm sticking by it 80-90mph one at that, Don is small, but not as small as he might appear! I expect the CATL wave to be labelled 91L tomorrow and there is about 30-40% chance we get a 4th named storm in July!
It already looks to be on it's way. Looking even better the past couple hours. I am talking about the wave in the Central Atlantic. Looking at Don this morning looked like he was on his deathbed but seems to be recuperating rapidly tonight.
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Quoting ProgressivePulse:
Evening All.

Rather impressive looking Don tonight.

Yeah, we're all rooting for goofy Don to smack Texas with a bunch of rain.
Seeing a little positive northward jog here.
LinkWVLoopGOM
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Quoting ProgressivePulse:
Evening All.

Rather impressive looking Don tonight.


Recon found the pressure between 994-996 mb.
Accurate.
Member Since: July 6, 2010 Posts: 113 Comments: 32262
1093. Patrap
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1092. Walnut
Quoting Thundercloud01221991:


Where are you getting your data from??? they may even have to issue a Hurricane Watch overnight why would they drop the warnings?
Don't feed the bears.
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Do they get sinkholes in Texas like in Florida when there are heavy rains after a drought?
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Evening All.

Rather impressive looking Don tonight.
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Quoting floridaboy14:
what will be the next advisory at 11pm for don?
a: 45
b: 50
c: 55-60
d:65
e: 70 im going with B

C, 60mph
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Quoting lucreto:
NHC will probably terminate all warnings (except maybe the Mouth of Rio Grande to Port Mansfield watch) at the 11pm advisory.


Where are you getting your data from??? they may even have to issue a Hurricane Watch overnight why would they drop the warnings?
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Quoting floridaboy14:
what will be the next advisory at 11pm for don?
a: 45
b: 50
c: 55-60
d:65
e: 70 im going with B


They don't typically use 55 mph, so C, 60 mph.
Member Since: July 6, 2010 Posts: 113 Comments: 32262
yeah, us too bohonkweatherman. we're pullin for ya!
Don just has to grow and then hit you with the best he's got. The more northerly the better. We're all praying for you. This crap has got to end. Sooner better than later!
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Quoting floridaboy14:
what will be the next advisory at 11pm for don?
a: 45
b: 50
c: 55-60
d:65
e: 70 im going with B


e
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what will be the next advisory at 11pm for don?
a: 45
b: 50
c: 55-60
d:65
e: 70 im going with B
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Quoting lottotexas:
hope ur wrong
Would not surprise Texans, this drought and heatwave show no mercy. Unbelievable Heat and Unbelievably dry, I have been thru some bad floods but this is worse because you have the drought and the heat to contend with. Right now the weather in Texas is not fit for any animal or any human IMO, of course i have only been here 53 years and I have only been following the weather closely for 40 years. This year is the worst because it is so Persistent and has lasted a long time. There are little to no breaks in the weather and to watch everything around you die with it being out of your control is tough for me to deal with. I feel so bad for the Americans who have flooded but I feel just as bad for those who are in this drought.
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1079. Patrap
00Z Multiplatform Satellite Surface Wind Analysis
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Quoting PRZEDCASTER:
Don looking real good right about to pump, it up !

Let's hope so.
Anything is better than nothing for TX right now imo.
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Quoting MrstormX:


I agree


+1
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Quoting Thundercloud01221991:


2 different planes recorded sub 1000 mb one recorded 996 and a half hour later the other recorded 995 it cant be bad data


I agree
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1075. emguy
There is a diferrence between invest and an area of interest...but the atlantic wave is the next item up for bid. Mean time, Don has formed himself a nest! Upper level low over mexico, another one approaching from the east, and Don is small and pinched between in the middle under a norrow ridge that is developing. Don may just take advantage of a remarkably small area of favorability, which may move in tandem with him to the coast. Another 2011 surprise, surprise...
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Quoting lucreto:

RECON got bad data Don's pressure is not below 1000 HPA


2 different planes recorded sub 1000 mb one recorded 996 and a half hour later the other recorded 995 it cant be bad data
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Quoting angiest:


Not sure what it does in that gap. Would seem to allow him room to move further north. But he still has a way to go before he gets in that layer.


Thank you I understand now.lol
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Don looking real good right about to pump, it up !
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1071. jdjnola
Quoting CanesfanatUT:


75% of the state is in exceptional drought. Hard to find a spot that doesn't need rain, eh?


Exactly. Besides, most of the moisture will likely fall in the worst parts of the drought even with a landfall due South of CC. (depending on how big Don is).
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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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