Don battling dry air and wind shear

By: Dr. Jeff Masters , 7:37 PM GMT en Julio 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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2304. TampaSpin 1:19 PM GMT on July 29, 2011 +0
Quoting stillwaiting:
,more than likely our first hurricane of the yr,looks like Emmy could become a major imo


YES........looks like a MAJOR and i BIG MAJOR....this is a giant turning tons of atmosphere.......i mean a bunch too.

The "Emily" storm name has always been major. Perhaps this one will get retired this year.
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Ahead of last year:
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Quoting tiggeriffic:


not saying it could/would happen....but wonder what would happen if a large hurricane was striking land just as a quake happened under water...what would the surge do...ugly thoughts just came to mind....


I'm afraid that would be horrible.
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Quoting tiggeriffic:


actually was thinking of east coast...Awendaw (just n of Charleston, SC) had a surge that was unbelieveable...people in 2 story houses had to get on their roofs because the second floor wasn't high enuf...


I did home inspection in the Bay St Louis, MS area after Katrina. I saw a 30+ foot sailboat on top of a 2 story home and the high water mark in a home I inspected was in the 3rd floor of the 3 story residence.
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Don looks like it's gaining an eye-like feature.
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Quoting NotCircumventing:
2360 ...

I think 6Z GFS sends 91L thru one of them.


to what degree?
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2365. Levi32
Good morning.

Blog update:

Tropical Tidbit for Friday, July 29th, with Video
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Looks like Don has remained a weak TS, and last few frames a little more northerly in its track. Continuing that trend would be a godsend to Texas. One of the few times where it is acceptable to wishcast a storm into the US coast I believe. In other news, 91L lost a bunch of convection the last few hours. Still has some dry air to deal with.
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Quoting tiggeriffic:


not saying it could/would happen....but wonder what would happen if a large hurricane was striking land just as a quake happened under water...what would the surge do...ugly thoughts just came to mind....



and a giant asteroid struck at the same time.
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When do I get to say Hebert's Box?? Too soon?
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2359. 7544
Quoting TampaSpin:



Puerto Rico, Bahamas, and South Florida might be in for a doozy with 91L.........i don't like this at all.


i always appricate your post and your knowledge along with other good opinions here but i think you may be right thanks keep up all u do
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Quoting taco2me61:
Ok so if 91L is named in 24hrs we will have our 5th named storm in July which could be another year like 2005.... And I donot like it at all....

Taco :o)
Even if it is named by Sunday, July 31st.
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Quoting ILwthrfan:


I noticed the other day the water temperatures from Miami east south east along the Islands down to Virgin Islands, that area to the north of that line is all above 85+ and is much above normal. It has really warmed up in that belt over the last week.

What is shear looking like for the future of 91-L?





Shear is a little high.....but, its within margins of slow development..
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Quoting TampaSpin:
I only put up 2 Floaters on 91L and left 5 up on Don......when Don is gone i will move 5 over to 91L! Dont wanna load up your computers.


Thanks Tampa but I am sure 5 will be needed after Don has landed in Texas and gone from the picture :o)

Taco :o)
Member Since: Julio 7, 2005 Posts: 6 Comments: 3261
Quoting taco2me61:


And Good Morning to you too while I'm having my 3rd cup of coffee....

Setup not looking good at all :o)

Taco :o)


my 3rd cup was b4 7am est lol...work 6am-6pm today...yay me but agree...set up NOT GOOD! They usually don't fly into storms that far away...wonder if it will spin up enuf visually for them to classify it b4 Monday...5 named storms by end of July would be absolutely CRAZY
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Quoting AussieStorm:
Hey all. What's the latest on TS Don?


Looks like he's going to stall in the GOM for about a week, turn into a Cat 4, make a sharp right, straddle the gulf coast all the way from South Padre Island to New Orleans, make another sharp right, develop into a Cat 5, then bust a U-turn and slam into New Orleans again.

No, really, it could happen!! Honest!!
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I only put up 2 Floaters on 91L and left 5 up on Don......when Don is gone i will move 5 over to 91L! Dont wanna load up your computers.
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Quoting TampaSpin:



Puerto Rico, Bahamas, and South Florida might be in for a doozy with 91L.........i don't like this at all.


I noticed the other day the water temperatures from Miami east south east along the Islands down to Virgin Islands, that area to the north of that line is all above 85+ and is much above normal. It has really warmed up in that belt over the last week.

What is shear looking like for the future of 91-L?
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Quoting TampaSpin:



Puerto Rico, Bahamas, and South Florida might be in for a doozy with 91L.........i don't like this at all.


Hey Tampa...how goes it? IMO not just FL...it will depend where around PR it hits and how weak/strong the trof is...not liking it at all...this one could be a sweeper and nail the whole east coast
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The organizing Blob near Panama should continue into the Pacific it appears......NO WORRIES for the ConUS with that one.
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2348. jpsb
Quoting tiggeriffic:


not saying it could/would happen....but wonder what would happen if a large hurricane was striking land just as a quake happened under water...what would the surge do...ugly thoughts just came to mind....
The tsunami would have more water to work with and go further inland, imho.
Member Since: Junio 30, 2009 Posts: 0 Comments: 1264
2347. Gearsts
Link
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Quoting tiggeriffic:


TACO!...not liking 91L at all...this one looks like it is gonna be an east coaster all the way...watching to see how close to PR it comes in the next 5 days... and to beat all...it puts it about 10-15 days out if it is an east coaster...and school starts here Aug 18...yay...just in time to delay school...woo hoo


And Good Morning to you too while I'm having my 3rd cup of coffee....

Setup not looking good at all :o)

Taco :o)
Member Since: Julio 7, 2005 Posts: 6 Comments: 3261
Quoting weatherh98:


i wonder what the state of louisiana would look like after this happened..... archepeligo here we come


actually was thinking of east coast...Awendaw (just n of Charleston, SC) had a surge that was unbelieveable...people in 2 story houses had to get on their roofs because the second floor wasn't high enuf...
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Quoting weatherman566:


Sorry, but I don't buy into the "hypercane" crap. Sounds like some science fiction/natural disaster fanatic trying to create a new storm that any weather weenie would love to see develop just to scare people.

500mph winds over water temperatures of 50C? Right...

,our world is always evolving,why would it be out of the question that the wx would,is their any question that wx was more extreme 10,000's of yrs ago??
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2341. WoodyFL
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See there is now a floater on 91L

Link
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Quoting stillwaiting:
...and it ain't forming out of the monsoon trough,gonna be a duzy,possible s.Florida theater????



Puerto Rico, Bahamas, and South Florida might be in for a doozy with 91L.........i don't like this at all.
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Quoting tiggeriffic:


not saying it could/would happen....but wonder what would happen if a large hurricane was striking land just as a quake happened under water...what would the surge do...ugly thoughts just came to mind....


i wonder what the state of louisiana would look like after this happened..... archepeligo here we come
Member Since: Junio 17, 2011 Posts: 11 Comments: 6539
blog freeze??? not time for an update...someone must be loading pics lol
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Quoting taco2me61:


I very much know this and there will be a lot of pepole in here will not like having to deal with "FEMA" (which as no "MONEY") and there insurance company leaving Town....

Tampa I know I donot like this setup as it is right now....

Taco :o)



YEPPERS.........you are so correct!
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Quoting weatherh98:


the only possible way a hypercane can form is if a meteor hits the ocean.... BBOOOOMM hypercane but thatss the only way im awareit can happen


not saying it could/would happen....but wonder what would happen if a large hurricane was striking land just as a quake happened under water...what would the surge do...ugly thoughts just came to mind....
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Quoting TampaSpin:



YES........looks like a MAJOR and i BIG MAJOR....this is a giant turning tons of atmosphere.......i mean a bunch too.
...and it ain't forming out of the monsoon trough,gonna be a duzy,possible s.Florida theater????
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It would be funny if 2011 Emily took the same path and had similar intensity to 2005 Emily.
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Quoting weatherman566:


Sorry, but I don't buy into the "hypercane" crap. Sounds like some science fiction/natural disaster fanatic trying to create a new storm that any weather weenie would love to see develop just to scare people.

500mph winds over water temperatures of 50C? Right...



the only possible way a hypercane can form is if a meteor hits the ocean.... BBOOOOMM hypercane but thatss the only way im awareit can happen
Member Since: Junio 17, 2011 Posts: 11 Comments: 6539
last major to go through the windwards was ivan. ???? i see the nhc pulled out a red card
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The models will flip.....flop.....
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Quoting taco2me61:


I very much know this and there will be a lot of pepole in here will not like having to deal with "FEMA" (which as no "MONEY") and there insurance company leaving Town....

Tampa I know I donot like this setup as it is right now....

Taco :o)


TACO!...not liking 91L at all...this one looks like it is gonna be an east coaster all the way...watching to see how close to PR it comes in the next 5 days... and to beat all...it puts it about 10-15 days out if it is an east coaster...and school starts here Aug 18...yay...just in time to delay school...woo hoo
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Keep one thing in mind with systems forecasted to take a track over the antilles then get lifted north by a trof: If the system experiences significant weakening over the islands, many times the system will become weak enough to slip under the trof against model consensus. We saw this with a couple of storms in 2004.

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Quoting NASA101:
One major model is not on board is the European - would like to some consensus from ECMWF - as currently it just shows a wave going through the Caribbean!


My sense on the Euro is that it hasn't been on board with anything once a system has a low pressure center. It'll develop vort area's and then drop them when they get more organized - been kinda weird from my perspective
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2326. GHOSTY1
P451 do you see a NNW change of direction on the noaa rainbow satellite loop? i just thought i noticed a new movement. Gotta Go.
Member Since: Julio 25, 2011 Posts: 0 Comments: 453
The blob north of Panama is huge!
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2322. jpsb
Quoting jasonweatherman2011:
i do not know if the trough will turn invesT 91L OUT TO SEA..the trough is much weaker now and moving out faster now
First does not 91L need to develop a bit before anything can pick it up? Not seeing development ATM, plus NHC gives it only 30% over then next couple of days. Now I am not an expert but until there is something to pick up I would not be worried about 91L being picked up.

91L is going thur the same environment as Don did, it took Don a while to develop so maybe it will take 91L a while too.
Member Since: Junio 30, 2009 Posts: 0 Comments: 1264
I guess it is possible the trough could play a factor with 91L and it's track but as is always with a system that has not even formed yet, it is way too early.

computer models are only as good as the variables that are put in them. Dry air, wind shear, trough, high pressure, water temps, steering currents, jet stream, etc....

If any one of these changes, the track could change.

best conclusion is stay tuned
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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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