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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Quoting Skeptic33:


So you're one of many that still believes that saturated fat and cholesterol consumption causes heart disease? That's the mainstream establishment's view yet they are completely wrong when you dig a little deeper in the literature...

Either way, both sides can be wrong.

Another great example - sun causing skin cancer... Dermatologists are screaming at us to avoid the sun and lather on massive amount of sunblock...

What does that do to us? Chronically low vitamin D level leading to significantly higher risk of getting one of 18 different cancers including skin cancer melanoma... multiple types of autoimmune disease, mental disorder, too many to list. Even autism...

So be careful of what you say... Even mainstream establishments can be wrong. Big time.

I haven't kept abreast of the debate about saturated fats, so I can't speak about that with any real depth of knowledge; I just know to limit my intake of them and exercise frequently. However, climate change has been observed through multiple lines of research, and that research has been independently verified multiple times by multiple sources. AGWT/ACCT is solid, and it's real. Now, an industry making hundreds of thousands of dollars in profit every minute of every day won't admit this, but the science is as solid as it gets. To what degree our burning of fossil fuels is contributing is really one of the last unsettled points, but even that appears to be somewhere between "most of it" and "all of it".

We are pumping 40 trillion liters a day of CO2 into the environment. That much of anything doesn't vanish without causing problems.

Anyway: back to the tropics, huh?
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2270. HarryMc
Quoting hurricaneben:
POLL: How strong will 91L get at peak?

a)Invest
b)TD
c)TS
d)CAT1
e)CAT2
f)CAT3-5


G= Too Early To Tell (TETT, new term)
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2269. NASA101
Remarkably good consensus from most of the models on 91L with bullseye south of PR in 4 days...

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Quoting jasonweatherman2011:
look like invest 91L GOING TO THE EAST COAST!!


And being recurved by a trough before it gets there.
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Quoting jasonweatherman2011:
look like invest 91L GOING TO THE EAST COAST!!
Well thats great news!!
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Quoting Skeptic33:


There are some models hinting a possible return of La Nina in the fall/winter. Not good. It's matter of where in Texas will feel full brunt of its effect. If we don't get anything from tropical systems, hope for El Nino to come... that always bring us above average amount of rainfall.


Yeah, there's not a lot of evidence or suggestions for an El Nino to return. Most reliable models suggest a neutral/La Nina conditions continuing.

Also, this year's La Nina was kinda abnormal. Negative NAO had a lot to do with the wacky winter storms across the Southeast/Northeast. Right now, we are in neutral conditions with an atmosphere still in a La Nina phase. Hopefully by this winter, the atmosphere will catch up to the neutral phase and perhaps lessen the extremes. However, something tells me that won't happen.
Member Since: July 15, 2008 Posts: 0 Comments: 108
Quoting Orcasystems:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 29th day of the month at 12:31Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number & Year: 04L in 2011
Storm Name: Don (flight in the North Atlantic basin)
Mission Number: 5
Observation Number: 04
A. Time of Center Fix: 29th day of the month at 11:57:50Z
B. Center Fix Coordinates: 25°49'N 94°21'W (25.8167N 94.35W)
B. Center Fix Location: 195 miles (314 km) to the E (92°) from Brownsville, TX, USA.
C. Minimum Height at Standard Level: 1,457m (4,780ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 40kts (~ 46.0mph)
E. Location of the Estimated Maximum Surface Wind: 11 nautical miles (13 statute miles) to the E (88°) of center fix
F. Maximum Flight Level Wind Inbound: From 165° at 52kts (From the SSE at ~ 59.8mph)
G. Location of Maximum Flight Level Wind Inbound: 42 nautical miles (48 statute miles) to the ENE (68°) of center fix
H. Minimum Sea Level Pressure: 1004mb (29.65 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,523m (4,997ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 21°C (70°F) at a pressure alt. of 1,527m (5,010ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 8°C (46°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 3 nautical miles
Remarks Section - Remarks That Were Decoded...
Maximum Flight Level Wind: 52kts (~ 59.8mph) in the east quadrant at 11:43:20Z
Maximum Flight Level Temp: 19°C (66°F) which was observed 13 nautical miles (15 statute miles) to the E (86°) from the flight level center
Remarks Section - Additional Remarks...
splash wind on the center drop was 30kts

so don didnt get any stronger? :(
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Quoting stoormfury:
hey SLU and mixed it seems that we might be in for it. only hope the radio stations start sensitising the people of what is to come. here again saint lucians are in party mood this holiday weekend. it was the same for TOMAS
We here in Barbados are also in a party mood for the long "Kadooment" weekend but i'm staying tune to what is happening.
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Actually the models have shifted more west.. the HWRF should be excluded for track but if you havent noticed as 91L leaves the carribean the models show it bending back wnw. pay attention to that and the TROUGH thats the key player how strong and how fast it goes
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Quoting hurricaneben:
POLL: How strong will 91L be at peak?

a)Invest
b)TD
c)TS
d)CAT1
e)CAT2
f)CAT3-5


F = First mayor hurricane
Member Since: Posts: Comments:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 29th day of the month at 12:31Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number & Year: 04L in 2011
Storm Name: Don (flight in the North Atlantic basin)
Mission Number: 5
Observation Number: 04
A. Time of Center Fix: 29th day of the month at 11:57:50Z
B. Center Fix Coordinates: 25°49'N 94°21'W (25.8167N 94.35W)
B. Center Fix Location: 195 miles (314 km) to the E (92°) from Brownsville, TX, USA.
C. Minimum Height at Standard Level: 1,457m (4,780ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 40kts (~ 46.0mph)
E. Location of the Estimated Maximum Surface Wind: 11 nautical miles (13 statute miles) to the E (88°) of center fix
F. Maximum Flight Level Wind Inbound: From 165° at 52kts (From the SSE at ~ 59.8mph)
G. Location of Maximum Flight Level Wind Inbound: 42 nautical miles (48 statute miles) to the ENE (68°) of center fix
H. Minimum Sea Level Pressure: 1004mb (29.65 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,523m (4,997ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 21°C (70°F) at a pressure alt. of 1,527m (5,010ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 8°C (46°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 3 nautical miles
Remarks Section - Remarks That Were Decoded...
Maximum Flight Level Wind: 52kts (~ 59.8mph) in the east quadrant at 11:43:20Z
Maximum Flight Level Temp: 19°C (66°F) which was observed 13 nautical miles (15 statute miles) to the E (86°) from the flight level center
Remarks Section - Additional Remarks...
splash wind on the center drop was 30kts
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possibly but you can already see the diffrence in models in the past few hours. before they were showing a more westward path, now a recurving beginning around the islands close to the east coast.

almost reminds me of last year. I know it is too early and things can change but just sayin
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Quoting Walshy:


It seems like 91L will not travel all the way through the Caribbean. After that, its anyone guess.


I'm thinking recurve, similar to Earl last year.
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POLL: How strong will 91L get at peak?

a)Invest
b)TD
c)TS
d)CAT1
e)CAT2
f)CAT3-5
Member Since: Posts: Comments:
2256. Gearsts
Quoting jasonweatherman2011:
wow!! look at the modeles now!! look like this storm going to the east coast!!
They will keep doing that with the track until we get a close low or a td.
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Don actually is quite disorganized structurally, which can be seen by this microwave image:

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2253. Walshy
Quoting kshipre1:
if I am reading this correctly, it seems like a recurve for 91L?


It seems like 91L will not travel all the way through the Caribbean. After that, its anyone guess.
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Looks like Mexico will get the rain, and Texas will get the scuddy thunderstorms. Landfall will probably be around Brownsville, an area that is only in a minor to moderate drought as well.

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Quoting barbados246:
I was just saying the same thing about preparing..although we should have had it done before


All I know is that this should be watched closely. We know already where Don is going but this one is not even formed yet. I will be calling my parents in PuertoRico today to let them know of the possibility. You can never be too prepared especially if you have little ones to look after. It would be wise for you to be prepared, not alarmed that's all.
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Quoting hurricaneben:
POLL: How strong will 91L be at peak?

a)Invest
b)TD
c)TS
d)CAT1
e)CAT2
f)CAT3-5

F, to be honest.
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2248. barbamz
Morning, Don.
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Quoting Tropicsweatherpr:


Agreed. And that is why from today,I am preparing to avoid the last minute rush.
I was just saying the same thing about preparing..although we should have had it done before
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POLL: How strong will 91L be at peak?

a)Invest
b)TD
c)TS
d)CAT1
e)CAT2
f)CAT3-5
Member Since: Posts: Comments:
if I am reading this correctly, it seems like a recurve for 91L?
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2244. SLU
29/1145 UTC 8.8N 41.2W TOO WEAK 91L -- Atlantic
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Quoting barbados246:
Good morning Jason what are your thoughts on 91L?
I am not Jason but I would keep a very close eye on this one if I were you. Levi and Kori both said last night it will be a problem for the Caribbean.
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Quoting ILwthrfan:
Remember 91L is going to go through the same environment that Don went through last week, so 91L may have some of the same issues that Don has had, unless conditions within the atmosphere have changed drastically since then.

91L does have a great ULC over him and he is going to be traveling over warmer and warmer waters throughout his lifetime from here on out. He has dry air all around him and all different levels of the atmosphere to his north and northwest. He will have to moisten is own environment up and tighten his up his circulation. This will take some time.


91L is much different than the wave that became Don. 91L is much more organized than that wave, and has a large moisture field with it.
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Quoting MrstormX:

Gracias


You should add the reflector site for the data to your google earth also.. then it always works...and you can show two HH AC at the same time if they are up.
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K, fess up. Who broke the blog this time?

Good morning.
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Quoting Orcasystems:


Airforce WC-1301

Gracias
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The BWS has declared that 91L will become Tropical Depression 5 in a few days. Apparently this is a legit player:



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I am not liking that look on Muifa's track forecast. Threatens China, Korea, the Okinawan and Ryukyu islands, main islands of Japan and will likely not recurve unless it makes a cyclonic track loop.
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Quoting jasonweatherman2011:
maybe INVEST 92L

Another one north of Panama!
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Remember 91L is going to go through the same environment that Don went through last week, so 91L may have some of the same issues that Don has had, unless conditions within the atmosphere have changed drastically since then.

91L does have a great ULC over him and he is going to be traveling over warmer and warmer waters throughout his lifetime from here on out. He has dry air all around him and all different levels of the atmosphere to his north and northwest. He will have to moisten is own environment up and tighten his up his circulation. This will take some time.
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Quoting jasonweatherman2011:
i do not see this happern
Good morning Jason what are your thoughts on 91L?
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Quoting Skeptic33:


So you're one of many that still believes that saturated fat and cholesterol consumption causes heart disease? That's the mainstream establishment's view yet they are completely wrong when you dig a little deeper in the literature...

Either way, both sides can be wrong.

Another great example - sun causing skin cancer... Dermatologists are screaming at us to avoid the sun and lather on massive amount of sunblock...

What does that do to us? Chronically low vitamin D level leading to significantly higher risk of getting one of 18 different cancers including skin cancer melanoma... multiple types of autoimmune disease, mental disorder, too many to list. Even autism...

So be careful of what you say... Even mainstream establishments can be wrong. Big time.


Always take both sides with a grain of salt. Don't eat 5 tubs of margarine and 10 eggs a day; don't spend 12 hours/day basking in the Sun. Times are changing as we speak.
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Quoting MrstormX:


I wish I could tell you, but my Google earth plugin isn't working and Im not even sure if it is an Air Force or NOAA plane in there.


Airforce WC-1301
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2229. JRRP
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Quoting floridaboy14:

I havent lol i need new info from the recon ! :) ive got a relative in Brownsville so im keeping them informed. so what are the hurricane hunters finding?


I wish I could tell you, but my Google earth plugin isn't working and Im not even sure if it is an Air Force or NOAA plane in there.
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2227. jpsb
Quoting floridaboy14:

well ive got some bad news... the CFS model trys to bring another moderate to strong la nina in the fall which would make the drought even worse..
It would be very hard to make it worse. I think longer is about all that can happen. This drought is already 2+ years, not sure how long it can go on, but another year is easily believable. I am giving up trying to grow most things in the spring and summer, hoping I can still have a productive fall garden we still get rain here in the winter/fall. Not a lot but enough with watering to keep a garden alive.
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Maybe the models are exagerating, but it is worth getting ready for. Rather be ready for nothing and eat the crow than sorry and getting eaten by the crow. Will be calling my family in PR to give them the heads up, not to alarm but to just let them know that it is that time of the year to get prepared.

GFS 06z Shear T=126hrs.



GFS 06z Vorticity T=126hrs.



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Significant Wind Levels...
Level Wind Direction Wind Speed
1004mb (Surface) 230 (from the SW) 30 knots (35 mph)
963mb 250 (from the WSW) 30 knots (35 mph)
924mb 255 (from the WSW) 19 knots (22 mph)
891mb 250 (from the WSW) 16 knots (18 mph)
854mb 275 (from the W) 11 knots (13 mph)
843mb 235 (from the SW) 8 knots (9 mph)

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Quoting MrstormX:
Looks like Mexico will get most of Don's heavy rain. I guess the blog has already moved on to 91L now.

I havent lol i need new info from the recon ! :) ive got a relative in Brownsville so im keeping them informed. so what are the hurricane hunters finding?
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Quoting stormhank:
I know its way early in the game to ask this , but could 91L possibly be a US threat??

LONG WAY OUT. There are 2 Factors though. we get a strong trough and once 91L is affecting the islands it gets hooked out of the islands possibly hitting Hispanola or Puerto and then recurving or a weak trough and it could hit the islands and move wnw towards the bahamas
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Looks like Mexico will get most of Don's heavy rain. I guess the blog has already moved on to 91L now.
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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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