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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18z GFS 96 hours out.. system in the Caribbean.
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470. JRRP

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Quoting tiggeriffic:


yes and the answer is in your scriptholder


So is the response
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Quoting tiggeriffic:
Hey Flood...Don has blown u a script


Heya Tig, ya doing good? what u think about Don and the other wave out there. I guess Flood disappeared I said hello and usually he always talks back.

sheri
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Quoting twincomanche:
A little creature that lives under a bridge and comes out to say totally irrelevant things.


Thought it was mothers house?
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Quoting CybrTeddy:
ATM there are 3 recons out heading for Don.

good lets see how strong our boy will get :) hurricane cant be ruled out right?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting MississippiWx:


Strengthening at the moment. I wouldn't doubt a 60mph tropical storm at the moment.


You must be right about those readings, they were probably mistakenly not flagged.
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Quoting CybrTeddy:
ATM there are 3 recons out heading for Don.
Honey they dont mess around when there is a system in the GOM do they.
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Quoting cat5hurricane:

Yeah, I read what you said. I know. And I agree.
This one I will just keep an eye on.The MJO should be coming in our basin soon when the wave reaches the carribean in a few days.
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ATM there are 3 recons out heading for Don.
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Quoting floridaboy14:

so is don weakining or stregnthining?


Strengthening at the moment. I wouldn't doubt a 60mph tropical storm at the next update.
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I see the HH data is turning everyone insane.
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Storm Relative 1km Geostationary Visible Imagery


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Quoting winter123:

So, about August 1 to November 1, right?
I'm almost out of time!


But it should be OK during that time if there are no storms in the EPAC/ATL.

As for Don, I'm thinking the forecast is pretty simple and I agree with the official forecast. WNW until Friday night landfall, 65mph. I don't think it will be a huge rainmaker, but significant, probably 3 inches along a 100 mile wide swath. It's moving pretty quick.


Sounds good to me. I like the funnies myself. I like the info that is given on this blog, but I like the funnies and reading some of the drama as well.
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Here is a new update from Corpus Christi.

"After some technical difficulties, I finally have the webcam up and running. 4G speed, too! :) Check it out at http://crazymother.tv/ I'm live from Corpus Christi, Texas. The hurricane party is postponed until sometime Friday, as there is not yet enough guidance for me to make plans."
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Quoting trollkiller2011:
Am I the only one in South Central Texas who DOESN'T want rain at my house?! I've been enjoying the drought as my hair stays more in place with the relative lack of humidity and precipitation (it's currently 103F here, I don't like the heat either but it's better than sultry weather).

More importantly though, I like the fact that the lack of rain has disallowed my front and back lawns from growing too much through most of the spring and so far in the summer. I like that it is brown and sickly looking as there are less bugs and other critters around in brown grass than green grass (I hate green grass). I've only had to mow 3 times all 2011 so far compared to 13 times by this time last year (El Nino rainy year). It poured nine days ago and portions finally started to grow again afraid that if it starts raining too much it'll grow too darn tall and green and I'll have to mow again. I hate mowing with a passion!!
Lol at your name.
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Quoting HimacaneBrees:
What's a troll?
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Quoting cat5hurricane:

Models are garbage beyond 5 days. Makes you wonder why so many are skeptical of Climate Change.
That's also why I said in the post that I'm not to sure on the models.They have developed systems off of the coast of Africa for the past few weeks and none have materialized.
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I wonder if the centers are stacked though - that mid level center could be recently reformed due to the strong convective burst.
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Quoting JrWeathermanFL:

They dont use 55mph?
I'm 99.99% sure.

They used it once last year and the blog went crazy (I think it was with Igor), lol.
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Quoting MississippiWx:


The rest of the readings from that batch were flagged. The reading was definitely contaminated.

so is don weakining or stregnthining?
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting catastropheadjuster:


what if there not flagged they are false? or is it if there flagged the false? I hope i said that right.

sheri


Flagged means they are suspect, but this is weird...how can the flight level winds be so low. There might be unflagged contamination.
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Quoting HimacaneBrees:
What's a troll?

Troll: an annoying person on the internet which his actions may include spamming, posting mostly off topic, or in some cases, hacking.
Member Since: November 13, 2009 Posts: 2 Comments: 728
Quoting MrstormX:


I agree, and this one isn't flagged either.


The rest of the readings from that batch were flagged. The reading was definitely contaminated.
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Good afternoon everyone.It looks like Don has Texas set in his sight.I pray they get sufficient rain there.Not too much mind ya.Too much of a good thing is a bad thing.Hope everyone is safe wherever it makes landfall.
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Also there are 45-50 knot readings - so if you discount the 50+ as contaminated you still have a 55mph system which appears to be organizing.
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Quoting VAbeachhurricanes:


give us a hint
mister perfect
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Quoting MrstormX:


I agree, and this one isn't flagged either.


what if there not flagged they are false? or is it if there flagged the false? I hope i said that right.

sheri
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Quoting MiamiHurricanes09:
Nope, that would indicate that the surface winds are contaminated/SFMR instrument isn't operating properly.

I doubt that Don is anything more than a 50-55mph tropical storm (yes, I know they don't use 55mph anymore).

They dont use 55mph?
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where did you hear that a thunderstorm in don had a 72 mph reading that would be a pretty darn large increase in windspeed, but it possibly just a gust from the storms.
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Well their are a lot of 50 knot readings and most of them are not flagged as suspect. Some are but those are closer to the center.
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Quoting cat5hurricane:

Not worried about a wave. Let's see if it develops into anything first. Though I don't think so.
Models suggest gradual development.Even though I'm not so sure of the models due to them being "off" this year.I looked at shear maps and shear looks favorable along with warm sst.The only problem is dry air.
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What's a troll?
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AF HH is wheels up from Biloxi
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Quoting stormpetrol:
Time: 21:52:30Z
Coordinates: 24.25N 91.35W
Acft. Static Air Press: 751.2 mb* (~ 22.18 inHg*)
Acft. Geopotential Hgt: 2,539 meters* (~ 8,330 feet*)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 154° at 11 knots (From the SSE at ~ 12.6 mph)
Air Temp: 14.3°C* (~ 57.7°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 12 knots (~ 13.8 mph)
SFMR Peak (10s) Sfc. Wind: 58 knots (~ 66.7 mph)
SFMR Rain Rate: 32 mm/hr (~ 1.26 in/hr)

Some very strong winds!


I agree, and this one isn't flagged either.
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Quoting VAbeachhurricanes:


Is that a riddle?


yes and the answer is in your scriptholder
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Quoting stormpetrol:
Time: 21:53:00Z
Coordinates: 24.2333N 91.3833W
Acft. Static Air Press: 751.7 mb* (~ 22.20 inHg*)
Acft. Geopotential Hgt: 2,533 meters* (~ 8,310 feet*)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 211° at 4 knots (From the SSW at ~ 4.6 mph)
Air Temp: 14.1°C* (~ 57.4°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 6 knots (~ 6.9 mph)
SFMR Peak (10s) Sfc. Wind: 63 knots (~ 72.4 mph)
SFMR Rain Rate: 37 mm/hr (~ 1.46 in/hr)

What's this?


Contaminated reading. You don't have a flight level wind of 6kts and then have a surface report of 63kts.
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Don is a real fighter.
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Quoting Patrap:




Mhmp(shrugs).Just when It seems Don will get no stronger and won't cuase any more problems than just rain he decides to intensify.Sneaky little critter.However that comes of no surprise though.
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Time: 21:52:30Z
Coordinates: 24.25N 91.35W
Acft. Static Air Press: 751.2 mb* (~ 22.18 inHg*)
Acft. Geopotential Hgt: 2,539 meters* (~ 8,330 feet*)
Extrap. Sfc. Press: -
D-value: -
Flt. Lvl. Wind (30s): From 154° at 11 knots (From the SSE at ~ 12.6 mph)
Air Temp: 14.3°C* (~ 57.7°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 12 knots (~ 13.8 mph)
SFMR Peak (10s) Sfc. Wind: 58 knots (~ 66.7 mph)
SFMR Rain Rate: 32 mm/hr (~ 1.26 in/hr)

Some very strong winds!
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Quoting trollkiller2011:
I used to be one of the good trolls back when I was a troll a loooong time ago, now I'm just a regular user who lurks and makes accounts to post on occasion because the WunderAdmins won't get over my 2007 actions (still holding grudges, like an idiot IMO).

I like the new numerical point system, reminds me of Youtube and Facebook.


give us a hint
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Quoting wn1995:


can you please tell me where i can get satellite data for google earth?


This what you are looking for?

http://www.nhc.noaa.gov/gis/

#1 of "Other NWS GIS Data"
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Quoting catastropheadjuster:


what are they finding?

sheri


Strong winds, though possibly contaminated.
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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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