Don battling dry air and wind shear

By: Dr. Jeff Masters , 7:37 PM GMT on July 28, 2011

Share this Blog
24
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1421 - 1371

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52Blog Index

Don might and i say might and only might make a landfall just below Hurricane force. It is still not very organized at the Lower levels by the evidence of a lack of Convergence. Until you have Convergence at the Lower Levels you WILL NOT HAVE much of a storm. That is just the way it is!!!!!
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Quoting want2lrn:


hey Shirl, it was actually Hola Amigos.........

LOL, I know which one that is! BV!
Member Since: July 15, 2005 Posts: 25 Comments: 341
Quoting j2008:

Someone correct me if im wrong but when a system has a 30 % is that when it can become an Invest?


No. I've seen invests when systems are at 10%. There is no set criteria for an invest, other than the discretion of a forecaster.
Member Since: March 7, 2007 Posts: 587 Comments: 20880
1417. JLPR2
Quoting GHOSTY1:
hopefully CATL will strengthen and for texas too. im asked for more than a tropical storm. Which way is it supposed to head anyway?


I tend to believe the ECMWF more than the GFS so to the Bahamas.
Member Since: Posts: Comments:
1416. angiest
Quoting doabarrelroll:

you have now asked for 2 storms to hit Texas in 10 minutes. Ignore listed.


That's not unreasonable for people to be wanting (within limits). Even the local NWS office as much as said we need the rains from Don, cause by the end of the weekend we will be back under the broiler.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting cctxshirl:

Which Met said that? DW Dale?
I did see that it's going a little south now. Could be the people who predicted Brownsville may be right.
Remember Dollie?


hey Shirl, it was actually Hola Amigos.........
Member Since: July 28, 2010 Posts: 0 Comments: 285
1414. j2008
Quoting stormpetrol:
8/40 30% by 1am CST.

Someone correct me if im wrong but when a system has a 30 % is that when it can become an Invest?
Member Since: December 19, 2008 Posts: 1 Comments: 224
Quoting P451:
SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...24.7N 92.5W

___

Don looks slightly better overall but as noted by quite a few observers it appears to be undergoing another weakening cycle. Let it do it's thing tonight and check in on it in the AM.

Since I did this at 5pm, and 8pm, one last one for 11pm.

As before the imagery is 45 minutes behind the center fix - so use your imagination and realize the convection has moved 10 miles or so further west since the image. Yet, for analysis and comparison sake, this will do fine.





====

8PM ET



====

5PM ET




------------------------

So clearly, Don has slowly found it's center more and more under the convection, but that center is located in the far north eastern part, with a good deal up to 90% of it's convection displaced to the south/south west due to continued northerly winds affecting the system.


Good night.


Your thoughts on the impressive wave in the Atlantic?
Member Since: Posts: Comments:
Quoting GHOSTY1:
weatherman566, i think it will strengthen quite a bit by the dmax tomorrow morning.


It's very possible. Intensity forecasts for small systems are incredibly difficult. I think Don will be a formidable tropical storm when it makes landfall though. We'll just have to wait and see. Where's the popcorn?
Member Since: Posts: Comments:
8/40 30% by 1am CST.
Member Since: April 29, 2007 Posts: 0 Comments: 7935
1409. GHOSTY1
hopefully CATL will strengthen and for texas too. im asked for more than a tropical storm. Which way is it supposed to head anyway?
Member Since: July 25, 2011 Posts: 0 Comments: 453
1407. angiest
Anyone know the approximate time the next CIMSS steering layers come out?
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Levi32:


I was speaking of satellite imagery in general, from which one can usually pick out a circulation relative to the storm, but not to the ground.
Oh ok.

Well thanks for clearing up the confusion
Member Since: Posts: Comments:
Quoting want2lrn:
Just an FYI for you all, local met just came on with the 10 coordinates. Saying what you all have been saying about intensity, BUT, moved the cone significantly to the south. We (Corpus) are in the upper portion of the cone now instead of in the middle and he hinted that we may see very little effects? Thoughts from anyone?

Which Met said that? DW Dale?
I did see that it's going a little south now. Could be the people who predicted Brownsville may be right.
Remember Dollie?
Member Since: July 15, 2005 Posts: 25 Comments: 341
Complete Update

TS BUSTED FORECAST ALIBI





Member Since: Posts: Comments:
Quoting DFWjc:


yes, they have, and a good song indeed...


Yes it is.
Member Since: Posts: Comments:
1401. Dennis8
Quoting remembercelia:
The forecast says Don should make landfall just south of Corpus Christi. Great, if this storm had "normal" structure. Problem is, most of the convection is SOUTH of the center. There is an area northeast of the CDO trying to wrap into the storm but other than that, the present forecast would give us about diddly squat.


Hello..I was 9 years old when Celia hit and it is the reason I got my meteorology education..are you in Corpus? I am in Houston.
Member Since: Posts: Comments:
Well good night everyone,
im expecting 50 to 60 mph Don in the morning, and 91L to be initiated, and by tomorrow afternoon it will have a 30 to 50% chance on it....
Member Since: October 3, 2010 Posts: 40 Comments: 4129
1399. GHOSTY1
weatherman566, i think it will strengthen quite a bit by the dmax tomorrow morning.
Member Since: July 25, 2011 Posts: 0 Comments: 453
Would be something if we saw 4 storms in July...

CATL wave looks good.



Member Since: Posts: Comments:





Still in the ITCZ i believe.....it needs to come out and maintain its own spin.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
1396. angiest
Quoting GHOSTY1:
Angiest, i totally agree Don has plenty of time before landfall and can change at a moments notice so it would be stupid to give up so soon.


Even if he maintain someone's getting something. Unless this is 2010 and your name is Bonnie, a storm in the GOM is practically 100% to hit someone.

(Yes, I know Bonnie made landfall in FL, on the Atlantic side, and I know her remnants hit the Gulf coast.)
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1395. KEEPEROFTHEGATE (Mod)
XX/AOI/XXL
Member Since: Posts: Comments:
1394. GHOSTY1
Angiest, i totally agree Don has plenty of time before landfall and can change at a moments notice so it would be stupid to give up so soon.
Member Since: July 25, 2011 Posts: 0 Comments: 453
1393. angiest
Quoting GHOSTY1:
im hopin' for an extra busy year for Texas, maybe that wave will head for texas and hopefully avoid land masses, shear, dry air for perfect strengthening conditions. If it does impact land i hope the Ike solution works out for it where the land causes an increase in size and therefore more rain. what am i doing, i guess wishful thinking.


I've been expecting an active year for the western GOM.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Tropical Storm Don is currently maintaining his strength, but it doesn't look like it's getting stronger at the moment as the strongest convection towards the center of the storm has diminished slightly. It still has a little bit of dry air that it has to fight off currently.

It could gain a little strength by Dmax tomorrow morning.
Member Since: Posts: Comments:
1391. Levi32
Quoting TomTaylor:
Ok then which product or satellite was it that was giving wind vectors relative to the storm?


I was speaking of satellite imagery in general, from which one can usually pick out a circulation relative to the storm, but not to the ground.
Member Since: Posts: Comments:
1390. j2008
CATL wave I'm guessing will be 30% and 91L at 2AM.
Should become Emily and may become our first real threat to the US. It may even be our first Major, I think that is pretty far our though.
Member Since: December 19, 2008 Posts: 1 Comments: 224
1389. 7544
Quoting reedzone:


WOW, this should be Invest 91L already... looks near TD status lol


agree looks to be moving fast too as it forms
Member Since: Posts: Comments:
1388. GHOSTY1
im hopin' for an extra busy year for Texas, maybe that wave will head for texas and hopefully avoid land masses, shear, dry air for perfect strengthening conditions. If it does impact land i hope the Ike solution works out for it where the land causes an increase in size and therefore more rain. what am i doing, i guess wishful thinking.
Member Since: July 25, 2011 Posts: 0 Comments: 453
1387. KEEPEROFTHEGATE (Mod)
04L/TS/D/Cx



weakening flag flag
Member Since: Posts: Comments:
1386. K8eCane
Please for Gods sake not up the East Coast. My wind deductible is 9000 dollars. I dont know how Travelers can get away with that
Member Since: Posts: Comments:
Quoting SouthFLNative:
Forget about Don, here comes Emily, this is beginning of a large circulation around 40 West. This could be a TS by Friday afternoon.
The looks of a classic Cape Verde Storm.

http://www.ssd.noaa.gov/goes/east/tatl/flash-avn. html


TS by tomorrow afternoon? Um no

Should be an invest already IMO, surprised its not
Member Since: Posts: Comments:
Quoting reedzone:


WOW, this should be Invest 91L already... looks near TD status lol


I'm watching that one close as I suspect it might track a tad south of Don and already be a hurricane in our area(Grand Cayman, CI)
Member Since: April 29, 2007 Posts: 0 Comments: 7935
1382. angiest
Quoting SouthFLNative:
Forget about Don, here comes Emily, this is beginning of a large circulation around 40 West. This could be a TS by Friday afternoon.
The looks of a classic Cape Verde Storm.

http://www.ssd.noaa.gov/goes/east/tatl/flash-avn. html


Why should we forget about Don 29 hours or so from landfall?
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting SouthFLNative:
Forget about Don, here comes Emily, this is beginning of a large circulation around 40 West. This could be a TS by Friday afternoon.
The looks of a classic Cape Verde Storm.

http://www.ssd.noaa.gov/goes/east/tatl/flash-avn. html


I live in TX and I'm ready to watch this one, Don is nothing
Member Since: Posts: Comments:
1380. j2008
Quoting floridaboy14:
im confused.. is don stregnthining or weakining or maintaining itself. i know its currently in DMIN

Strengthening slowely.
Member Since: December 19, 2008 Posts: 1 Comments: 224
Forget about Don, here comes Emily, this is beginning of a large circulation around 40 West. This could be a TS by Friday afternoon.
The looks of a classic Cape Verde Storm.

http://www.ssd.noaa.gov/goes/east/tatl/flash-avn. html
Member Since: Posts: Comments:
1378. GHOSTY1
so that new wave yall think is going to become a storm in the next few days since it has a circulation already, where do you think it will go?
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting jasonweatherman2011:
look at 40 west!!


WOW, this should be Invest 91L already... looks near TD status lol
Member Since: Posts: Comments:
im confused.. is don stregnthining or weakining or maintaining itself. i know its currently in DMIN
Member Since: Posts: Comments:
1375. KEEPEROFTHEGATE (Mod)
still image latest

Member Since: Posts: Comments:
1374. GHOSTY1
RitaEvac, i have no problem with that and if the NHC said it that works this adds a new element of strengthening to me and i like stronger storms. Im still predicting CC or Rockport, Tx landfall
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting TropicalAnalystwx13:


idk, I just remember somebody mentioning OSCAT or something like that, than Levi talking about how it isn't that accurate.
yeah, well you were right it was the OSCAT. Never heard of it until the other day.

I recall them mentioning it but just figured it was actually the ASCAT lol
Member Since: Posts: Comments:
Quoting floridaboy14:


It dropped from the last update.
Member Since: July 6, 2010 Posts: 113 Comments: 32347
Quoting stormpetrol:


I'm watching that one real close could be TD by saturday and a TS sunday IMO.


Well, it already has a closed circulation. What it needs now is convection and wind speeds.
Member Since: July 6, 2010 Posts: 113 Comments: 32347

Viewing: 1421 - 1371

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52Blog Index

Top of Page

About

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

Local Weather

Overcast
57 °F
Overcast