Don battling dry air and wind shear
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
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i say the high is gonna lift up then flatten out before it can make a recurve...
91L could really be the first strong hurricane of the season...
Which would send it here! Thanks!
lol.
Well, I finished my projection late Wednesday night and came up with landfall between Delray Beach and Boca Raton. That's just my own long range projection though and is for course only.
That's been the general pattern to date. Otherwise would be a pretty big pattern change.
Ok I posted this once but it did not show up....
I think our time is running out and our luck is on a "Very Thin Line "
Not liking this at all and Good Morning to you too :o)
Taco :o)
LOCATION...26.2N 94.9W
ABOUT 190 MI...305 KM SE OF CORPUS CHRISTI TEXAS
ABOUT 165 MI...260 KM E OF BROWNSVILLE TEXAS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES
Not while it's 2600 miles away.
This is gonna be all about timing.......pure and simple!
9/10/89 later named hugo was a TD 13.2n 20.0w
9/11/89 became TS Hugo 12.5n 29.2w
9/13/89 became Hurrican Hugo 12.8n 43.5w
understand that it was 2 months in the season later, however, our higher than normal sst's could be a BIG contributing factor as far as the season goes
I sure hope you're right. We need the rain up here.
agreed levi but if i may ask, if 91L becomes a weak hurricane in the NE carribean does that gurantee a recurvutrue or do we just have to wait and see each day as the pattern progresses?
I am having flashbacks to Earl last year from the model runs for the new Invest..will it or wont it..watching in NC
You and me both.
Drive down to Corpus tomorrow. You'll get a rainy Saturday for sure!
July 28th, 1995~ TS Dean formed, and July 30th hit texas
July 28th, 2011~ TS Don formed, and july 30th will hit TX
Climatology is creepy...
didnt they show don in the bahamas north of the islands? its a long way out but are there only 2 track scenarios levi?
LOL!
+100
SW caribbean could be 92L soon too, just saying
I'm in CC right now-work here, live in Rockport.
Nothing on the horizon so far. And I'm on the bayfront.
No doubt a sight for sore eyes...
then again ........MAYBE NOT>.........LOL
TROPICAL STORM DON DISCUSSION NUMBER 8
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042011
1000 AM CDT FRI JUL 29 2011
SATELLITE IMAGES SHOW THAT DON HAS BECOME A LITTLE BETTER ORGANIZED
THIS MORNING WITH INCREASED CONVECTIVE BANDING AROUND THE CENTRAL
CONVECTION...ESPECIALLY IN THE SOUTHERN SEMICIRCLE. HOWEVER...THE
STORM CONTINUES TO EXPERIENCE 10-15 KT OF NORTHERLY VERTICAL WIND
SHEAR...WITH AN ELONGATED OVERALL CLOUD PATTERN AND A STREAM OF ARC
CLOUDS IN THE EASTERN AND NORTHEASTERN QUADRANTS OF THE CYCLONE.
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS REPORTED 850 MB
FLIGHT-LEVEL WINDS OF 51 KT...AND THE CENTRAL PRESSURE ESTIMATED
FROM THE AIRCRAFT DATA IS NEAR 1002 MB. THE INITIAL INTENSITY
REMAINS 45 KT.
THE INITIAL MOTION IS NOW 300/12. DEEP-LAYER RIDGING OVER THE
SOUTHEASTERN UNITED STATES SHOULD STEER DON GENERALLY
WEST-NORTHWESTWARD UNTIL THE CYCLONE DISSIPATES OVER LAND IN
36-48 HR. THE NEW FORECAST TRACK HAS CHANGED LITTLE FROM THE
PREVIOUS TRACK AND IS NEAR THE CENTER OF THE TRACK GUIDANCE
ENVELOPE.
DON SHOULD CONTINUE TO EXPERIENCE MODERATE SHEAR UNTIL THE CENTER
MAKES LANDFALL IN ABOUT 18 HR. IN ADDITION...WATER VAPOR IMAGERY
AND MICROWAVE PRECIPITABLE WATER DATA SHOW DRY AIR CLOSE TO THE
WESTERN SIDE OF DON. THIS COMBINATION SHOULD CONTINUE TO IMPEDE
SIGNIFICANT STRENGTHENING BEFORE LANDFALL...AND THUS THE INTENSITY
FORECAST SHOWS ONLY SLIGHT STRENGTHENING. DON SHOULD WEAKEN
STEADILY AFTER LANDFALL...AND THE SYSTEM IS EXPECTED TO DISSIPATE
COMPLETELY BY 48 HR IN AGREEMENT WITH THE DYNAMICAL MODEL GUIDANCE.
INTERESTS IN EXTREME NORTHEAST MEXICO SHOULD CONTINUE TO CLOSELY
MONITOR THE PROGRESS OF DON. ANY SMALL DEVIATION TO THE SOUTH OF
THE FORECAST TRACK COULD NECESSITATE THE ISSUANCE OF WARNINGS FOR
THE EXTREME NORTHEASTERN COAST OF MEXICO.
FORECAST POSITIONS AND MAX WINDS
INIT 29/1500Z 26.2N 94.9W 45 KT 50 MPH
12H 30/0000Z 26.8N 96.7W 50 KT 60 MPH
24H 30/1200Z 27.7N 99.1W 35 KT 40 MPH...INLAND
36H 31/0000Z 28.3N 101.6W 25 KT 30 MPH...INLAND
48H 31/1200Z...DISSIPATED
$$
FORECASTER BEVEN
SW caribbean(pre 92L) Franklin...
91L, Emily
or the other way around... possible
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