Tropical Storm DON

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TROPICAL STORM DON DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
400 AM CDT FRI JUL 29 2011
 
DON CONTINUES TO HAVE A SHEARED APPEARANCE ON SATELLITE IMAGES WITH
THE LOW-LEVEL CENTER DISPLACED NEAR THE NORTHERN EDGE OF AN
ELONGATED AREA OF STRONG CONVECTION.  THIS SHEAR CAN ALSO BE SEEN
IN RECONNAISSANCE DATA...WHICH SHOWED THAT THE SURFACE CENTER IS
DISPLACED SOMEWHAT TO THE NORTH OF THE 850 MB FLIGHT-LEVEL CENTER. 
THE INITIAL INTENSITY REMAINS 45 KT...A BLEND OF THE ESTIMATES FROM
SATELLITE AND AIRCRAFT DATA.
 
MODERATE NORTHERLY SHEAR IS FORECAST UNTIL DON MAKES LANDFALL ALONG
WITH SOME DRY AIR ALOFT.  THIS COMBINATION WILL PROBABLY LIMIT
SIGNIFICANT INTENSIFICATION EVEN THOUGH THE STORM IS MOVING OVER
VERY WARM WATERS.  MOST OF THE GUIDANCE SHOWS JUST A LITTLE MORE
STRENGTHENING...AND THE OFFICIAL INTENSITY FORECAST IS BASICALLY AN
UPDATE OF THE PREVIOUS PACKAGE.  AFTER MOVING THROUGH TEXAS...THIS
SMALL SYSTEM WILL NOT LAST VERY LONG AFTER INTERACTING WITH THE
HIGH TERRAIN OF MEXICO...AND DISSIPATION IS LIKELY BETWEEN 36 AND
48 HOURS.
 
AIRCRAFT FIXES SUGGEST DON IS MOVING ABOUT 295/12.  HIGH PRESSURE
RIDGING OVER THE SOUTHERN UNITED STATES WILL PROBABLY STEER THE
CYCLONE ALONG THAT GENERAL COURSE UNTIL LANDFALL...PERHAPS EVEN A
LITTLE MORE TO THE LEFT AS THE RIDGE BUILDS.  THE GUIDANCE IS IN
GOOD AGREEMENT...ALTHOUGH THE USUALLY RELIABLE ECMWF MODEL IS
FARTHER TO THE NORTHEAST.  AN EXAMINATION OF THE ECMWF FIELDS
INDICATES THAT THE MODEL DECOUPLES THE LOW- AND MID-LEVEL
CENTERS...ALLOWING DON TO MOVE MORE TO THE NORTHWEST.  THIS DOES
NOT SEEM LIKELY AS ENVIRONMENTAL CONDITIONS ARE NOT EXPECTED TO
CHANGE SIGNIFICANTLY FROM NOW UNTIL LANDFALL.  THUS THE NHC
FORECAST WILL STAY CLOSE TO THE DYNAMICAL MODEL CONSENSUS AND THE
PREVIOUS FORECAST.
 
INTERESTS IN EXTREME NORTHEAST MEXICO SHOULD CLOSELY MONITOR THE
PROGRESS OF DON. AN UNEXPECTED 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  29/0900Z 25.3N  93.6W   45 KT  50 MPH
 12H  29/1800Z 26.1N  95.5W   50 KT  60 MPH
 24H  30/0600Z 27.0N  97.8W   45 KT  50 MPH...INLAND
 36H  30/1800Z 27.8N 100.4W   30 KT  35 MPH...INLAND
 48H  31/0600Z...DISSIPATED
 
$$
FORECASTER BLAKE/STEWART
 
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