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#8484 (Received by flhurricane at: 10:47 AM 15.Sep.2004) TCDAT1 TROPICAL STORM JEANNE DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT WED SEP 15 2004 SATELLITE IMAGERY AND WSR-88D RADAR DATA FROM SAN JUAN SUGGEST THAT JEANNE MAY BE SUFFERING FROM SHEAR AND DRY AIR INTRUSION THIS MORNING. THE LOW LEVEL CENTER IS AT THE SOUTHERN EDGE OF THE PRIMARY CONVECTION...AND THE OUTER BANDING HAS BECOME SOMEWHAT RAGGED COMPARED TO YESTERDAY. SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM TAFB AND SAB...AND 45 KT FROM AFWA. DOPPLER RADAR WINDS SUGGESTS SURFACE WINDS OF ABOUT 55-60 KT. BASED ON ALL THE ABOVE... THE INITIAL INTENSITY WILL BE 60 KT. THE INITIAL MOTION REMAINS 295/7. THERE IS LITTLE CHANGE IN THE TRACK FORECAST PHILOSOPHY. JEANNE IS CURRENTLY ON THE SOUTHERN PERIPHERY OF A DEEP LAYER RIDGE...AND MODEL GUIDANCE AGREES THAT THIS RIDGE SHOULD PERSIST AND MOVE JEANNE ON A CONTINUED WEST-NORTHWEST MOTION THROUGH ABOUT 48 HOURS. BEYOND THAT TIME...THE SOLUTIONS SOMEWHAT DIVERGE...OWING TO DIFFERENCES IN HOW EACH MODEL HANDLES A WEAKENING IVAN OVER THE SOUTHEASTERN UNITED STATES AND HOW MUCH RIDGING WILL REMAIN OVER THE EXTREME WESTERN ATLANTIC. MOST OF THE DYNAMICAL GUIDANCE CALLS FOR JEANNE TO TURN NORTHWESTWARD AND EVEN NORTHWARD AFTER 48 HR. ON THE OTHER HAND...THE GFDL IS A LEFT OUTLIER...CALLING FOR JEANNE TO TRACK ACROSS THE DOMINICAN REPUBLIC AND THE BAHAMAS TO SOUTH FLORIDA BY DAY 5. THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS PACKAGE WITH A LITTLE MORE NORTHWARD MOTION AFTER 96 HR. THE FORECAST TRACK IS TO THE LEFT OF ALL THE DYNAMICAL GUIDANCE SAVE THE GFDL AND FSU SUPERENSEMBLE. THE INTENSITY FORECAST REMAINS A CHALLENGE. AN UPPER-LEVEL TROUGH OR CYCLONIC SHEAR AXIS IS CURRENTLY JUST WEST OF JEANNE AND CAUSING SHEAR. LARGE-SCALE MODELS HAVE A VARIETY OF IDEAS FOR THE EVOLUTION OF THIS FEATURE...FROM PERSISTING FOR THREE OR MORE DAYS TO ALMOST INSTANT DISSIPATION. MOST LIKELY ENOUGH THIS FEATURE WILL CREATE ENOUGH SHEAR TO AT LEAST SLOW INTENSIFICATION FOR 48-72 HR...AND THIS IS REFLECTED IN THE INTENSITY FORECAST. AFTER THAT...JEANNE SHOULD MOVE INTO A MORE FAVORABLE ENVIRONMENT AND GRADUALLY STRENGTHEN. ANOTHER COMPLICATION IS LAND INTERACTION. PASSAGE OVER PUERTO RICO MAY AT LEAST SLOW DEVELOPMENT...AND IF JEANNE MOVES OVER OR NEAR THE DOMINICAN REPUBLIC ALL BETS ARE OFF ON THE INTENSITY FORECAST. IT SHOULD BE NOTED THAT JEANNE COULD STILL BECOME A HURRICANE BEFORE REACHING PUERTO RICO. EVEN IF IT DOES NOT...HURRICANE FORCE WINDS ALOFT SEEN ON THE SAN JUAN RADAR WILL AFFECT HIGHER ELEVATIONS. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 15/1500Z 17.8N 65.8W 60 KT 12HR VT 16/0000Z 18.3N 66.9W 65 KT 24HR VT 16/1200Z 19.2N 68.6W 65 KT 36HR VT 17/0000Z 20.2N 70.4W 65 KT 48HR VT 17/1200Z 21.1N 71.9W 65 KT 72HR VT 18/1200Z 23.0N 74.5W 70 KT 96HR VT 19/1200Z 25.5N 76.5W 75 KT 120HR VT 20/1200Z 28.0N 77.5W 80 KT |