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#536230 (Received by flhurricane at: 10:59 PM 22.Aug.2012) TCDAT4 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 |