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Tropical Storm ISAAC (Text)

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TROPICAL STORM ISAAC DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
1100 PM AST WED AUG 22 2012
 
AN AIR FORCE HURRICANE HUNTER AIRCRAFT INVESTIGATED ISAAC SEVERAL
HOURS AGO AND FOUND THAT THE CENTER WAS STILL NOT WELL-DEFINED AND
THE INTENSITY ESTIMATE OF 40 KT WAS PROBABLY A LITTLE ON THE HIGH
SIDE.  HOWEVER...DROPSONDE DATA FROM A NOAA AIRCRAFT CURRENTLY
INVESTIGATING THE STORM SUGGEST THAT THE CENTER HAS PROBABLY BECOME
A LITTLE BETTER DEFINED AND THAT THE MINIMUM PRESSURE HAS DROPPED A
BIT.  THERE HAS ALSO BEEN AN INCREASE IN COLD-TOPPED CONVECTION
NEAR AND OVER THE ESTIMATED CENTER SO THE CURRENT INTENSITY IS HELD
AT 40 KT.  ISAAC HAS DEVELOPED AN IMPRESSIVE UPPER-LEVEL OUTFLOW
PATTERN AND DYNAMICAL GUIDANCE SHOWS THAT THE VERTICAL SHEAR SHOULD
REMAIN WEAK DURING THE NEXT SEVERAL DAYS.  THEREFORE THE PRIMARY
IMPEDIMENT TO STRENGTHENING SHOULD BE THE INTERACTION WITH THE
MOUNTAINOUS TERRAIN OF HISPANIOLA AND EASTERN CUBA.  THE MOST
RECENT RUNS OF THE HWRF AND GFDL SHOW SIMILAR AMOUNTS OF LAND
INTERACTION BUT ARE NOT IN GOOD AGREEMENT ON THE INTENSITY FORECAST
AS THE FORMER MODEL SHOWS MUCH LESS STRENGTHENING THAN THE LATTER.
THE OFFICIAL WIND SPEED FORECAST IS IN REASONABLE AGREEMENT WITH
THE LATEST STATISTICAL-DYNAMICAL GUIDANCE.

AFTER A SLIGHT SOUTHWARD RELOCATION OF THE CENTER...THE INITIAL
MOTION CONTINUES BASICALLY WESTWARD OR 270/17.  ISAAC SHOULD
CONTINUE TO MOVE WESTWARD TO WEST-NORTHWESTWARD FOR THE NEXT COUPLE
OF DAYS ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE.  THE
GLOBAL MODELS CONTINUE TO DEPICT A BREAK IN THE RIDGE IN THE
VICINITY OF FLORIDA IN SEVERAL DAYS...WHICH SHOULD INDUCE A MORE
NORTHWARD COMPONENT OF MOTION.  THE ECMWF MODEL SHOWS LESS OF A
BREAK IN THE RIDGE THAN THE GFS SOLUTION.  CONSEQUENTLY...THE ECMWF
TRACK IS SOMEWHAT TO THE SOUTHWEST OF MOST OF THE OTHER TRACK
MODELS WHICH WOULD LESSEN THE THREAT TO FLORIDA.  THE OFFICIAL
TRACK FORECAST FOR THIS ADVISORY IS QUITE CLOSE TO THE PREVIOUS ONE
AND ALSO VERY CLOSE TO THE DYNAMICAL MODEL CONSENSUS.

FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0300Z 15.8N  63.0W   40 KT  45 MPH
 12H  23/1200Z 16.2N  65.4W   45 KT  50 MPH
 24H  24/0000Z 16.9N  68.1W   55 KT  65 MPH
 36H  24/1200Z 17.5N  70.5W   65 KT  75 MPH
 48H  25/0000Z 18.6N  72.7W   55 KT  65 MPH
 72H  26/0000Z 21.5N  77.0W   60 KT  70 MPH...ON NORTH COAST OF CUBA
 96H  27/0000Z 24.0N  80.5W   65 KT  75 MPH
120H  28/0000Z 27.0N  83.5W   70 KT  80 MPH
 
$$
FORECASTER PASCH
 
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