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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Quoting P451:


Look at the condition of the system and the condition of the clouds to Don's north.

Look over the satellite imagery - different IR bands too - and you will see this 10 to 15 knots of shear is clearly wrong. It is MUCH higher.





If it was higher than 10-15 knots, the center would be exposed. Instead, the system is becoming better organized. It's not as high as you are advertising.

As I said before, the small size of the system makes it more susceptible to lower wind shear than larger systems can deal with.
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Quoting uptxcoast:


And eat at the Boiling Pot!!!!!!


I've been wanting to eat there but havent yet, but did see the windmill blade in the tree, i have been to the italian restraunt and it was awesome hope nothin' happens to it for anything down there
Member Since: Julio 25, 2011 Posts: 0 Comments: 453
Quoting GHOSTY1:
what is the dMax i have been heard thrown around?


The flare up of convection seen during the early morning hours is known as diurnal maximum.
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what is the dMax i have been heard thrown around?
Member Since: Julio 25, 2011 Posts: 0 Comments: 453
Quoting angiest:


If that happens, at least he shouldn't be strong enough to mess up the hotel we stay at in Fulton. It is right across from Fulton Harbor.

If you ever find yourself in the Rockport-Fulton area (assuming you haven't ever done this), visit Fulton Mansion. About 2 blocks back from the mansion (on what used to be the same property) there is a big oak tree in the front yard of what may be an abandoned house. In that tree is a very unusual object: The "wheel" of a windmill, blades and all. It was deposited there by the 1919 Corpus Christi hurricane.


And eat at the Boiling Pot!!!!!!
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Quoting P451:


Look at the condition of the system and the condition of the clouds to Don's north.

Look over the satellite imagery - different IR bands too - and you will see this 10 to 15 knots of shear is clearly wrong. It is MUCH higher.





Center isn't exposed though. If the shear was higher than 15kts it would be exposed. This small system is easily susceptable to 15kt wind shear, moreso than a stronger system.
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Quoting Tazmanian:



lol it looks like DON wants too go too MX


I like Don Julio tequila. I wonder if this is that Don.. Maybe he's tired of sea water and want's a shot of tequila. I mean he's been tasting sea water since he left Africa. just sayin'
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Quoting floodzonenc:
From the NHC... Tropical Storm Don has been struggling with negative self-esteem which it has been feeling in his core.  Expect gradual strengthening as WU blogosphere becomes more favorable later this evening....



ROFLMAO, that was good i really think that they should at that to the NHC outlook
Member Since: Julio 25, 2011 Posts: 0 Comments: 453
Quoting Tazmanian:



lol it looks like DON wants too go too MX


Last frames seem to move it more to the WNW

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Quoting CybrTeddy:
Most of the computer models are also saying a decent vort max will develop on our side from this.

even if it did, it most likely wont develop and would get shoved into central america. our 2 prime areas of concern are Don and the TW at 40W
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Don is a 45mph TS that is small - they are must more vulnerable to shear compared to larger and stronger systems. On visible images you can see outflow from the large convective cluster making it about 50 miles to the north where it collides with the shear from the ridge. This distance has been increasing as the central convection strengthens and Don moves away from the shear axis. Soon Don should begin to slowly strengthen as central convection develops on the north side of the CoC - maybe only 20 or 30 miles worth but that is enough to form an inner core. Now if the shear increases this could all fall apart but if it remains below 15 knots Don should be able to fight it off.
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256. wpb
both gfdl and hmrf have handle don v well.

best performance of the season.
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Quoting jpsb:
What the heck, landfall between Matagorda bay and Galveston bay, TS with max winds of 50-60 mph.
I say Freeport
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hyperanthony, i just started yesterday and everyone on the blogs are knowledgeable about the weather so you will learn alot.
Member Since: Julio 25, 2011 Posts: 0 Comments: 453
thought they'd pull a yellow card on the system in the atlantic?
Member Since: Septiembre 11, 2010 Posts: 1 Comments: 4920
Quoting sunlinepr:



lol it looks like DON wants too go too MX
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Quoting hurricanehunter27:
Highly unlikly, not sure the faults in the area can produce a 9.0.
they said that about japan as well its ok lets built them right here by the beach its ok you will never see anything stronger then what we built them for anyway
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Quoting floodzonenc:

Welcome hyper!  Seems that shear is stronger than the map is indicating...  Don is still struggling with it.


Okay cool, thanks for the heads up!
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Quoting angiest:
Re: the eartquake discussion. Each 1 point (so 4 to 5 for intance) increase in magnitude is 33x the energy. Fours and 5s won't let out a lot compared to a 7 or 8.

my background is geophysics, earthquake seismology is one of my major interests (i don't practice in the field, however.)


Thanks, good facts to take in consideration....
So that would mean that even if we had 10 / 3.3 in mag. shakes, that would be similar to having just one 5.0?
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247. jpsb
Quoting GHOSTY1:
Im still for a Rockport landfall just north of CC
What the heck, landfall between Matagorda bay and Galveston bay, TS with max winds of 50-60 mph.
Member Since: Junio 30, 2009 Posts: 0 Comments: 1197
Most of the computer models are also saying a decent vort max will develop on our side from this.
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Shear is currently less than it was earlier today. The NE quadrant is not pancaked flat like it was earlier today.
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Quoting floridaboy14:

by alot of shear you mean 10 to 15 knots right?


Yeah I was gonna say its not that there is a lot of shear affecting Don, its more that it's a small system that is easily impacted by 15kt shear.
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i wouldn't be surprised if Don's state wasn't because of the wind shear and the dry air but because of all the hating on him by most of the people on the blogs. Even when he's starting to consolidate and possibly more powerful people still hate on him.
Member Since: Julio 25, 2011 Posts: 0 Comments: 453
Quoting JrWeathermanFL:


A few days ago a vid on here said a 9.0 could happen off shore of PR. This would mean a tsunami for the U.S. The guy said that activity should be increasing.
Highly unlikly, not sure the faults in the area can produce a 9.0.
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Quoting P451:
...DON MOVING BRISKLY NORTHWESTWARD WITH LITTLE CHANGE IN
STRENGTH...


SUMMARY OF 400 PM CDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...24.9N 91.3W
ABOUT 425 MI...690 KM ESE OF CORPUS CHRISTI TEXAS
ABOUT 395 MI...635 KM E OF BROWNSVILLE TEXAS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES

==============
While the image is 45 minutes older than the center fix this still illustrates just fine what poor shape Don is in. CIMSS shear map is obviously far from reality. There is a LOT of shear devastating Don.



Not a lot of shear, just enuf to hurt don, rember does not take much with a systeme the size of don.
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Quoting KEEPEROFTHEGATE:
may mean a big slip coming


A few days ago a vid on here said a 9.0 could happen off shore of PR. This would mean a tsunami for the U.S. The guy said that activity should be increasing.
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Re: the eartquake discussion. Each 1 point (so 4 to 5 for intance) increase in magnitude is 33x the energy. Fours and 5s won't let out a lot compared to a 7 or 8.

my background is geophysics, earthquake seismology is one of my major interests (i don't practice in the field, however.)
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I'm very happy to see more convection blowing up around the center of Don. I just really wish the dry air and northerly shear would diminish so he could breathe a little bit. We need Don to increase in size so he can provide more rainfall for portions of Southeast Texas.

Regardless of what happens, Don can only be seen as a good thing. (Minus the random tornadoes in the NE Quadrant)
Member Since: Julio 15, 2008 Posts: 0 Comments: 108
Quoting StormJunkie:
Hey tigger :)

And Keith, that'd be a K for Krystal...And no thank-you! I have swore those things off for the rest of my life thanks to this crew...lol


Guilty as charged and damn proud of it!!!!!

How are you SJ? Don't get to see you much these days.
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Quoting P451:
...DON MOVING BRISKLY NORTHWESTWARD WITH LITTLE CHANGE IN
STRENGTH...


SUMMARY OF 400 PM CDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...24.9N 91.3W
ABOUT 425 MI...690 KM ESE OF CORPUS CHRISTI TEXAS
ABOUT 395 MI...635 KM E OF BROWNSVILLE TEXAS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES

==============
While the image is 45 minutes older than the center fix this still illustrates just fine what poor shape Don is in. CIMSS shear map is obviously far from reality. There is a LOT of shear devastating Don.





He isn't being affect by a lot of shear, it is his small size that makes weaker shear that wouldn't normally affect larger systems shear him.

Either way, he isn't having as much of a problem now.
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Quoting P451:
...DON MOVING BRISKLY NORTHWESTWARD WITH LITTLE CHANGE IN
STRENGTH...


SUMMARY OF 400 PM CDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...24.9N 91.3W
ABOUT 425 MI...690 KM ESE OF CORPUS CHRISTI TEXAS
ABOUT 395 MI...635 KM E OF BROWNSVILLE TEXAS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES

==============
While the image is 45 minutes older than the center fix this still illustrates just fine what poor shape Don is in. CIMSS shear map is obviously far from reality. There is a LOT of shear devastating Don.




by alot of shear you mean 10 to 15 knots right?
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231. j2008
Quoting Daveg:
Question... the models seem to be bouncing back and forth from more northward to more southward.

What would be causing them to do that, and it is likely that the NHC track will tend to stay more where it is unless the tracks stop that back and forth?

Not sure what causes it, but my guess is that the NHC would want to keep an average of what the models are saying. That is how they make thier cone, so I think it is safe to say that the cone will stay the same if all the models stay the same and vice versa.
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Quoting TropicalAnalystwx13:


And she peaked at 65 mph. Very possible at this time.



other 65mph TS
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Quoting KEEPEROFTHEGATE:
hes got o lets say 19hrs 45min remain before final destination by this time tomorrow nothing more but some words for the books


Don shouldn't make landfall until Saturday morning.
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Hey everyone! Long time lurker, first time poster (like so many others).



I'm trying to learn and get a handle on these maps... it looks like Don is moving into wind shear at 5-10 kts, so will he have a better shot at continued development as he moves out of the higher shear?

Thanks, and hope it brings some much-needed rain for TX!
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Looks like that energized mid Atl. spin is there to stay....

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Quoting StormJunkie:


Yeah, agree completely...But the deal was people would give money to disaster relief if I ate something like 15 of them in two hours...Without throwing up.



Whats upp Stormjunkie???? Good to see ya on here :o)
and want to say thank you for all you did for Joplin and in Alabama :o) My mom lives up there in Joplin and from what she has told me it is still very "Bad" if you know what I mean....

Anyway Thank You my Friend

Taco :o)
Member Since: Julio 7, 2005 Posts: 6 Comments: 3261
Quoting Daveg:
Question... the models seem to be bouncing back and forth from more northward to more southward.

What would be causing them to do that, and it is likely that the NHC track will tend to stay more where it is unless the tracks stop that back and forth?


I have the same question as you. After lurking in the blog all afternoon, I got the feeling that the models were going to shift north again. Then the 4:00 post shifted back south. I am so confused! :S
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Quoting Daveg:
Question... the models seem to be bouncing back and forth from more northward to more southward.

What would be causing them to do that, and it is likely that the NHC track will tend to stay more where it is unless the tracks stop that back and forth?


Its their projection on the strength of the ridge, and if I had my guess based on sat imagery i would say a little to the south of the current forecast track.
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Quoting GHOSTY1:


And i expect that number to steadily increase because some people just don't see the whole picture that he's moving into favorable environment and will strengthen and possibly weaken but its not over till its over.
hes got o lets say 19hrs 45min remain before final destination by this time tomorrow nothing more but some words for the books
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Quoting MiamiHurricanes09:
Don's current structure reminds me of Fiona from last year.

Conditions were somewhat similar.


And she peaked at 65 mph. Very possible at this time.
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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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