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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1621. GHOSTY1
MTWX i understand what people got so angry about but i mean they shouldn't have assumed and jumped to conclusions, im no sadistic person who wants death and destruction i dont want death or destruction just a large very wet system. But thank you for simplifying that for me i better watch what i post. Kudos for simplifying it with me because some of the others didnt want to be rational about it.
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k
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1619. pottery
Quoting CybrTeddy:
Not bad.

Not good, either...

:):))
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1618. j2008
Quoting GHOSTY1:
where are yall expecting landfall?
Just south of CC 50%
North of Brownsville 40% Anywhere else 10 %. All depends on how strong he gets.
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Member Since: August 2, 2010 Posts: 21 Comments: 9887
Not bad.
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1615. MTWX
Quoting angiest:


To the north of PR is a transform (strike-slip) boundary between the Caribbean Plate and the North American Plate. This boundary transitions to a subduction zone at the Puerto Rico Trench to the NE of PR. The transform boundary is unlikely to produce earthquakes over about magnitude 8-8.2 (and probably lower than that, most transform faults can't generate the higher magnitude earthquakes). The subduction boundary could produce 8+. That is the type of boundary that produces the strongest earthquakes (for instance, the handful of confirmed 9.0+ magnitude earthquakes have all been on sunduction zones).

good information to know. Thanks!
Member Since: July 20, 2009 Posts: 23 Comments: 1394
Quoting GHOSTY1:
where are yall expecting landfall?


Where the NHC says it is going to...
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Quoting GHOSTY1:
another problem with the drought in texas and around houston is that the city is sink because underground aquafers or whatever there called are becoming so empty that the ground weight and additional weight from buildings is causing the area to sink causing major foundation damage especially in my area of NW Houston.


Its like that here in Pearland...one day I went outside, got in my gpas truck, looked at the house and was like huh? Got out, the brick around the garage leaned to the right, breaking the fascia board and pulling away from the wood around the garage door. 2 years ago the heat and dryness cracked our newly installed tile floor, and there are cracks in the sheetrock now. Thank God for the few crazy thunderstorms we have had, but we still need 15-20 inches of rain to catch up. Don was some hope, but now really no hope.
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1612. GHOSTY1
this is off topic but im watching louie on FX while blogging and its the perfection combination to me
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1611. angiest
Quoting sunlinepr:
16 small quakes today from 2.5 to 4.6. There were 27 / 2 days ago




To the north of PR is a transform (strike-slip) boundary between the Caribbean Plate and the North American Plate. This boundary transitions to a subduction zone at the Puerto Rico Trench to the NE of PR. The transform boundary is unlikely to produce earthquakes over about magnitude 8-8.2 (and probably lower than that, most transform faults can't generate the higher magnitude earthquakes). The subduction boundary could produce 8+. That is the type of boundary that produces the strongest earthquakes (for instance, the handful of confirmed 9.0+ magnitude earthquakes have all been on sunduction zones).
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1610. j2008
BTW Don already has a sub 1000 pressure. its 998, I expect by the next update it will be 996 or 997. I dont expect it to rise any, Don hasnt shown any weakening and in fact this new burst probably will strengthen it even more before the update. Love to hear your feedback on my analysis.
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1609. MTWX
Quoting GHOSTY1:
Nielson-Gammon the states climatologist for texas said that it would be just like a drop in the bucket for texas but that drop is a start and if its just a drop why am i receiving so much flak for asking for a more potent rain maker i dont understand the logic behind some of yall, asking for multiple systems to help us is wrong i guess.

Don't get the wrong idea. Problem was you mentioned a name of a particularly, devestating storm that got people fired up, and kept wishing for Don to get stronger. What Texas needs is a line of large waves/depressions that just slowly drift over the state. Minimal damage, good constant moderate rainfall.
Member Since: July 20, 2009 Posts: 23 Comments: 1394
1608. GHOSTY1
where are yall expecting landfall?
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Good nite everyone.........LONG DAY TOMORROW!
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Quoting MississippiWx:


I didn't say it's below 1000mb now...I said it probably will. :-)
Ahh sorry. In that case, I agree. It's almost there already ;~)
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Member Since: August 2, 2010 Posts: 21 Comments: 9887
1604. pottery
Quoting JLPR2:


I wish that one would develop and move due north straight to the fishes.
Not looking like that will happen anytime soon.

Quoting angiest:



Looks like West Bound and Down.

Thats what it looks like, right now.
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Quoting SouthDadeFish:
Not yet, the burst has only recently covered the center. If recon stays for one more fix I think we'll see a reading at 999mb. Question is, how long will this burst last before a collapse?


I didn't say it's below 1000mb now...I said it probably will. :-)
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1601. jpsb
Quoting angiest:


Glad to hear they are getting out of your hair. ;) Note I did say that we needed something with the rain shield (and forward speed!) of Ike, and not the wind and surge.
Surge was the problem with Ike, cat 2 winds but cat 4 surge. Most places here just could not handle a 13 foot tide. My dirt is 12' up so I only got 1 foot of water in the house. You would be surprised what 1 foot of salt water can do. Plus the Marina next to me wound up in my front yard.
Member Since: June 30, 2009 Posts: 0 Comments: 1586
That wave from the Atl. would be our major concern...

Member Since: August 2, 2010 Posts: 21 Comments: 9887
Don reminds me of afternoon summer thunderstorms here in the South. Our NWS office calls them pulse thunderstorms. They quickly develop intense updrafts, only to have a downdraft 15 minutes later and the convection disappears soon after. The upper support just isn't there for sustained convection.
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Polo
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16 small quakes today from 2.5 to 4.6. There were 27 / 2 days ago


Member Since: August 2, 2010 Posts: 21 Comments: 9887
Quoting MississippiWx:
I would imagine the pressure will go down below 1000mb again in this new burst of convection.
Not yet, the burst has only recently covered the center. If recon stays for one more fix I think we'll see a reading at 999mb. Question is, how long will this burst last before a collapse?
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Quoting Tygor:
Wow I can't believe this isn't going to affect Central Texas. I thought for sure it would get us.


Per #1579 JLPR2 graphic you can see the NW winds from Don probing Austin. The high pressure we have is not supposed to allow that. Hold tight.
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1594. j2008
Quoting taco2me61:
ok what happened to the Blog????

Marco?????

Taco :o)

Polo!! Just a blog malfunction. It happens.
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1593. JLPR2
Quoting pottery:
Good evening.
Looking at 40w, and not liking what I'm seeing there.
Dont like the present Steering either...
Not happy about this one.


I wish that one would develop and move due north straight to the fishes.
Member Since: September 4, 2007 Posts: 7 Comments: 8748
1592. angiest
Quoting pottery:
Good evening.
Looking at 40w, and not liking what I'm seeing there.
Dont like the present Steering either...
Not happy about this one.


Looks like West Bound and Down.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1591. GHOSTY1
Nielson-Gammon the states climatologist for texas said that it would be just like a drop in the bucket for texas but that drop is a start and if its just a drop why am i receiving so much flak for asking for a more potent rain maker i dont understand the logic behind some of yall, asking for multiple systems to help us is wrong i guess.
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YOu can see the tilt here..........





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ok what happened to the Blog????

Marco?????

Taco :o)
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1588. pottery
Good evening.
Looking at 40w, and not liking what I'm seeing there.
Dont like the present Steering either...
Not happy about this one.
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Quoting GHOSTY1:
thats it, you got it i wanted to say that but i was unsure, thank you. We travel that route because at night if you go down 35 to rockport there is a reststop about 10 miles from rockport where you can see the stars and the milky way perfectly, sometimes lightning bugs and coyotes get close.


Sounds lovely. Haven't looked at the stars and listened to the coyotes since I lived in El Paso. We definitely have less trees around now, but the mosquitoes are the size of jumbo jets. Sigh. ;)
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1586. GHOSTY1
SouthDadeFish, i agree they call him pathetic all the time and like you said he's a fighter and i referred him to a marine earlier because he takes a beating and keeps kicking, but he's not the best marine (and i may be offending some marines if they don't feel the same way)
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Quoting SouthDadeFish:
I'm not sure he will either, but I don't get why people are calling him pathetic. He is a fighter. He's overcome a lot, and continues to pulsate. He will bring much needed rain to Texas. I've seen much worse looking tropical storms.


Yes Bonnie of last year :o)

Taco :o)
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1584. jpsb
Quoting angiest:


You only recently discovered you live two miles from the coast? Glad you don't sleep walk...
My front yard is Galveston bay. If yall like I'll post pics of my house after Ike, very sad, but at least I still had a house! I was one of the lucky ones.
Member Since: June 30, 2009 Posts: 0 Comments: 1586
1583. Tygor
Wow I can't believe this isn't going to affect Central Texas. I thought for sure it would get us.
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Quoting j2008:

Do we have a new HH mission going on? Cause if thats from the last mission, thats not the center pressure, they missed the center.


That update was from about 10 minutes ago and they weren't in the center.
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I would imagine the pressure will go down below 1000mb again in this new burst of convection.
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1580. j2008
Quoting MississippiWx:
1001mb on the last update from the aircraft.

Do we have a new HH mission going on? Cause if thats from the last mission, thats not the center pressure, they missed the center.
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1579. JLPR2
Nice comeback for Don; for a second I thought it wasn't going to refire quickly.
Member Since: September 4, 2007 Posts: 7 Comments: 8748
Quoting cat5hurricane:
Don looks awful. Poor guy. I'm still thinking that Mexican landfall is in store.

I see we have a near yellow blog out there. 20%. We'll monitor.
maybe awful compared to other moderate tropical storms, but compared to earlier, Don is looking about as good as he ever has.
Member Since: August 24, 2010 Posts: 19 Comments: 4358
Quoting SouthDadeFish:
I'm not sure he will either, but I don't get why people are calling him pathetic. He is a fighter. He's overcome a lot, and continues to pulsate. He will bring much needed rain to Texas. I've seen much worse looking tropical storms.


Yeah, he's not pathetic by any means. Just a moderate strength tropical storm, which is perfect for drought relief.
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Quoting TampaSpin:
Little humor here....and not about weather but.....i had to post this.....LOL!

So my Niece's WON in their age group and are both PIG MUD WRESTLER Winners at the 4th fair.............OMG. LOVE IT!


I Like for sure and Very Funny Too :o)

Taco :o)
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1575. angiest
New steering for Don:



A tad tricky. He has a little time to gain some latitude , but not much. I wish they had data for 17Z, would have been easier to make sense. At this point I guess I will shift from Matagorda to Freeport to Matagorda to North Padre.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1574. GHOSTY1
too bad for me though with college starting next month i'm moving to huntsville for Sam houston state university and that will make it harder for me to go to CC and Rockport and to watch the tropics but i'll learn to work it out.
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Quoting MississippiWx:


Eh, I don't think Don is ever going to be able to sustain these bursts of convection. He hasn't his whole lifetime.
I'm not sure he will either, but I don't get why people are calling him pathetic. He is a fighter. He's overcome a lot, and continues to pulsate. He will bring much needed rain to Texas. I've seen much worse looking tropical storms.
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1001mb on the last update from the aircraft.
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Quoting SouthDadeFish:
Well it did have an 8mb drop in an hour and a half. I would almost consider that rapid intensification. The process came to a quick halt through ingestion of dry air that collapsed the convective complex. However, he is bursting nicely as we speak.

Link


Had conditions been favorable, it could have been rapid intensification. Point is, they are not.
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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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