Don battling dry air and wind shear

By: Dr. Jeff Masters , 07:37 PM GMT em 28 de Julho de 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: 521 - 471

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

Member Since: Posts: Comments:
Quoting washingtonian115:
Honey I wish I could help.I go to this site called crownweather to get most of the information.If that helps....


Washingtonian, Thanks I'll go over there and see what i can find.
sheri
Member Since: Posts: Comments:
Quoting GHOSTY1:
Nigel, remember last night when we were the last few bloggers and we called Don a marine that's what he is and he's fightin' and getting stronger. Ooooh Raaah!!
It's amazing how unpredictable some of these storms can be.
Member Since: Posts: Comments:
Quoting SevereWeatherAddict:
As you can see I very rarely post. But what is the changes of Don becoming a cat 1 ? And thanks in advanced.


The chances are still there and decent but quite less than it was at this time yesterday. I'd say there's a 25% chance of this becoming a hurricane, down from 40% yesterday.
Member Since: Posts: Comments:
I haven't seen the high-density obs, but from the quotes on here a couple pages back, 58kts SFMR wind with 11kts at flight-level has to raise eyebrows. That is more than likely an inaccurate reading.
Member Since: Posts: Comments:
Quoting SevereWeatherAddict:
As you can see I very rarely post. But what is the changes of Don becoming a cat 1 ? And thanks in advanced.
I think its got a 50/50
Member Since: Posts: Comments:
Yesterday I posted
"Don will go down as one of the MOST beneficial TS since records were kept. He will make landfall with a paltry windspeed of 50-55 mph. There will be sustained tropical rains and mild breezes that will put a massive dent in the Texas and maybe even New Mexico droughts. There will be no loss of life and minimal property damage. Maybe a tree limb or 2 will fall, but even this could be a good thing because tree limbs have to go sooner or later. If my vision works out, thank you Don."
Looking like a home run so far!
Member Since: Posts: Comments:
Quoting Levi32:
Checking in for break. Can't wait to dive into data from multiple planes when I get home.

Levi your back! how long can you stay on the blog and the 18z gfs brings that central atlantic tropical wave as a 1007mb low into the carribean further south.. and also don looks to be stregnthining.. any thoughts?
Member Since: Julho 25, 2011 Posts: 0 Comments: 1102
Quoting catastropheadjuster:


Tig thanks for the answer. I've asked different questions to folks on her but since I'm a nobody I guess they don't need answering. Have a good night.

sheri


sheri, it happens all over the place...you have to ask the right peeps...the ones i trust are Patrap, Flood, Levi, Presslord, and a few others...too many trolls this year...
Member Since: Setembro 16, 2007 Posts: 0 Comments: 3650
On rapid-scan I am seeing less in the way of spiral banding associated with an exposed circulation, meaning increased organization.
Member Since: Posts: Comments:
Quoting tiggeriffic:


hey Sheri...good as to be expected...still think Don is going to go outside the models and get stronger than they think...also think it wont be as far south as they think...the high that was supposed to guide it moved faster than expected (we were supposed to get rain on the SC coast till friday and it lifted out before 5pm yesterday)...



See you were right with your "gut" feeling. We should never ignore them.
Member Since: Posts: Comments:
Quoting nigel20:
AThanks for the info it was very informative
Quoting TomTaylor:
no problem
hey tom, good job on the ins and outs of whats going on in there, no, what do ya say? lets hit the waves!
Member Since: Posts: Comments:
It's starting to rock out there!

http://www.ndbc.noaa.gov/station_page.php?station =42001
Member Since: Posts: Comments:
Austin area not expecting much from Don but may not hit 100 Saturday, forecast is only 98.

TROPICAL STORM DON continues on a NW track. We expect landfall late Friday night or early Saturday AM along the lower coast of Texas. Slight strengthening is possible before landfall, but it will likely stay below hurricane strength. Computer models Thursday afternoon have shifted the forecast track a bit farther south, which is not good news for our rain chances. Once Don arrives, it will not linger. By Sunday it will already be out in West TX with our rain chances quickly coming to an end.


In the short term, a few spotty showers appeared on radar Thursday, but most areas missed out. Mostly clear skies will turn mostly cloudy by Friday morning with lows in the upper 70s. We'll call for isolated showers and storms (20%) on Friday as Gulf moisture continues to pour in to TX ahead of Don. It will still be hot with temps in the upper 90s to near 100, and feeling hotter with the humidity. The slight rain chance continues Friday night,.


Once Don makes landfall Saturday, the heaviest rain will likely be south of our area. Parts of South Texas may see 3-5" or more. Latest projections indicate the potential for a half inch or less near Austin, with heavier totals southward, and less northward. We're calling for a 30% chance in Austin.
Member Since: Julho 5, 2009 Posts: 0 Comments: 1348
As you can see I very rarely post. But what is the changes of Don becoming a cat 1 ? And thanks in advanced.
Member Since: Posts: Comments:
Quoting P451:


I think it will. We may see one more lull and see the current activity pushed southward but if so I think another burst would take over later.

As of now 90% or more of Don's convection is south of the surface center.

I'm interested to compare the 5pm position/satellite (I did so in a post further back) to an 8pm counterpart.

At 5pm the center was at or barely under the nothernmost fringe of the large convective mass.

While there is argument over whether or not the CIMSS shear values are correct or not - what is obvious is strong northerly winds continue to drive Don's convection south of the center.

I want to take a look at continuity between 5pm and 8pm and see if he's improved this situation and by how much.

Too many folks looking at the large blowup of convection and aren't noting where it is in relation to the center - giving a false sense that it's a well organized and intensifying system - when it's clearly not as of 5pm.


===============
This was as of 5pm, et, along with the center fix placed over the visible imagery:

...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.






Recon has confirmed that the surface center is south of there and more in line with the convection.
Member Since: Posts: Comments:
..Don is venting Houston,, Copy?


Member Since: Posts: Comments:
Quoting tiggeriffic:


hey Sheri...good as to be expected...still think Don is going to go outside the models and get stronger than they think...also think it wont be as far south as they think...the high that was supposed to guide it moved faster than expected (we were supposed to get rain on the SC coast till friday and it lifted out before 5pm yesterday)...


Tig thanks for the answer. I've asked different questions to folks on her but since I'm a nobody I guess they don't need answering. Have a good night.

sheri
Member Since: Posts: Comments:
Quoting MiamiHurricanes09:
Notice the closed isobar north of Honduras. It moves over the Yucatan and develops into a tropical cyclone in the BOC.
I'm glad someone else noticed besides me.....
Member Since: Posts: Comments:
Quoting VAbeachhurricanes:


So is the response


AMEN!
Member Since: Setembro 16, 2007 Posts: 0 Comments: 3650
Gosh, I love rapid scan. Anyway, Don appears to be producing enough heat now to fight off the shear effects. In other words, he is starting to produce his own anticyclone in the upper levels. That is why we are seeing such an improvement in the outflow:

Member Since: Posts: Comments:
Quoting catastropheadjuster:


Washingtonian, Hey do you know what the MJO chart looks like I don't know how to find it. Computer crashed and everything I have saved all these yrs is gone.

sheri
Honey I wish I could help.I go to this site called crownweather to get most of the information.If that helps....
Member Since: Posts: Comments:
Quoting MississippiWx:


1007mb low pressure associated with it...Looks like the GFS wants a tropical cyclone now too.
Notice the closed isobar north of Honduras. It moves over the Yucatan and develops into a tropical cyclone in the BOC.
Member Since: Posts: Comments:
Quoting twincomanche:
It's pretty tough in here when the only person offering anything remotely like some real information is our resident high school kid. Thanks Tom. The rest of you sheesh!


Lighten up, Frances! LOL
Member Since: Posts: Comments:
Don Tejas' say's to Michael..



There just wasnt enuf time,,Michael.....
Member Since: Posts: Comments:
Checking in for break. Can't wait to dive into data from multiple planes when I get home.
Member Since: Posts: Comments:
Quoting catastropheadjuster:


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


hey Sheri...good as to be expected...still think Don is going to go outside the models and get stronger than they think...also think it wont be as far south as they think...the high that was supposed to guide it moved faster than expected (we were supposed to get rain on the SC coast till friday and it lifted out before 5pm yesterday)...
Member Since: Setembro 16, 2007 Posts: 0 Comments: 3650
Okay since I can't get a damn question answered around here I'll look into myself.Looks like the model has a system or area of low pressure off of the Yucatan as well.
Member Since: Posts: Comments:
Quoting trollkiller2011:
CybrTeddy...you know better than to trust the long range GFS.


96 hours out is hardly long range as 300+ hours out are.
Member Since: Posts: Comments:
Quoting DFWjc:


I'm still going with Aransas Pass...
i say San Diego California,Don gonna live across 1500 miles of desert and mountains, and emerge into the pacific ocean, become a Cat 1 Hurricane in 70 degree water and slam the Hotel Cel on Coronado Island CA.
Member Since: Posts: Comments:
Quoting VAbeachhurricanes:
Time: 22:21:30Z
Coordinates: 30.1333N 89.1167W
Acft. Static Air Press: 725.3 mb (~ 21.42 inHg)
Acft. Geopotential Hgt: 2,905 meters (~ 9,531 feet)
Extrap. Sfc. Press: 1016.2 mb (~ 30.01 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 184° at 11 knots (From the S at ~ 12.6 mph)
Air Temp: 10.5°C (~ 50.9°F)
Dew Pt: 7.8°C (~ 46.0°F)
Peak (10s) Flt. Lvl. Wind: 11 knots (~ 12.6 mph)
SFMR Peak (10s) Sfc. Wind: 27 knots (~ 31.0 mph)
SFMR Rain Rate: 1 mm/hr (~ 0.04 in/hr)
(*) Denotes suspect data
---

HH wheels up.


Thanks...Didn't realize we would have multiple flights.
Member Since: Posts: Comments:
Don is strengthening? That would mean a more southerly landfall right?
Member Since: Posts: Comments:
will they pull the yellow after seeing that gfs?
Member Since: Setembro 11, 2010 Posts: 1 Comments: 4891
Is it official that some of the readings were contaminated? or did it get really strong?
Member Since: Posts: Comments:
Just when I got into the conversation about the wave seems like others re bringing it up.I'm not to faithful in the models right now.Seeing that they've forecasted several storms to from off of Afica.And none have occured.Maybe because they were early in the season.
Member Since: Posts: Comments:
Quoting CybrTeddy:
18z GFS 96 hours out.. system in the Caribbean.


1007mb low pressure associated with it...Looks like the GFS wants a tropical cyclone now too.
Member Since: Posts: Comments:
Time: 22:21:30Z
Coordinates: 30.1333N 89.1167W
Acft. Static Air Press: 725.3 mb (~ 21.42 inHg)
Acft. Geopotential Hgt: 2,905 meters (~ 9,531 feet)
Extrap. Sfc. Press: 1016.2 mb (~ 30.01 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 184° at 11 knots (From the S at ~ 12.6 mph)
Air Temp: 10.5°C (~ 50.9°F)
Dew Pt: 7.8°C (~ 46.0°F)
Peak (10s) Flt. Lvl. Wind: 11 knots (~ 12.6 mph)
SFMR Peak (10s) Sfc. Wind: 27 knots (~ 31.0 mph)
SFMR Rain Rate: 1 mm/hr (~ 0.04 in/hr)
(*) Denotes suspect data
---

HH wheels up.
Member Since: Posts: Comments:
Quoting JrWeathermanFL:
Is it me or does it look like Don is heading to mexico?



Nope...just you
Member Since: Posts: Comments:
Quoting CybrTeddy:
18z GFS 96 hours out.. system in the Caribbean.
Quoting JRRP:

Things could get ugly...
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:



BEST TROLL POST I HAVE EVER!!

GOOD ONE KEEP :)
Member Since: Posts: Comments:
Quoting washingtonian115:
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.


Washingtonian, Hey do you know what the MJO chart looks like I don't know how to find it. Computer crashed and everything I have saved all these yrs is gone.

sheri
Member Since: Posts: Comments:
Nigel, remember last night when we were the last few bloggers and we called Don a marine that's what he is and he's fightin' and getting stronger. Ooooh Raaah!!
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
mister perfect


Say it ain't so...
Member Since: Posts: Comments:
Quoting JRRP:

Storm in the pacific storm in the Atlantic.What's that by the Yucatan?.
Member Since: Posts: Comments:
Way better visible structure on this as well, I recall many strong TS/low end canes with a similar look. Claudette ('09) and Humberto ('07) come to mind.

Member Since: Posts: Comments:
18z GFS 96 hours out.. system in the Caribbean.
Member Since: Posts: Comments:

Viewing: 521 - 471

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

Mist
36 °F
Neblina