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| #536779 (Received by flhurricane at: 5:02 AM 25.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 500 AM EDT SAT AUG 25 2012 THE CIRCULATION OF ISAAC HAS REMAINED RELATIVELY INTACT AFTER MOVING ACROSS THE SOUTHWESTERN PENINSULA OF HAITI OVERNIGHT. BEFORE THE CENTER MOVED INLAND...HURRICANE HUNTER AIRCRAFT DATA SUGGESTED THAT THE CYCLONE HAD PEAK WINDS OF ABOUT 55 KT. ASSUMING THE CYCLONE WEAKENED A LITTLE AFTER ENCOUNTERING THE HIGH TERRAIN...THE INITIAL INTENSITY IS LOWERED TO 50 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 320/12. AS A MID-LEVEL TROUGH LIFTS OUT OF THE SOUTHEASTERN UNITED STATES...ISAAC WILL MOVE GENERALLY WEST-NORTHWESTWARD AROUND THE WEST SIDE OF THE SUBTROPICAL RIDGE FOR THE NEXT THREE DAYS OR SO...AND THEN TURN NORTHWARD LATE IN THE PERIOD AS A SHORTWAVE TROUGH AMPLIFIES OVER THE EASTERN UNITED STATES. THERE HAS BEEN LITTLE CHANGE TO THE NHC FORECAST THIS CYCLE...AND THE NEW TRACK FORECAST IS CLOSE TO THE MIDDLE OF THE GUIDANCE ENVELOPE AND LIES CLOSE TO THE GFS AND THE TVCA MULTI-MODEL CONSENSUS THROUGH 96 HOURS. BY DAY 5 THERE IS SOME DISAGREEMENT AS TO WHETHER ISAAC WILL TURN NORTHEASTWARD AHEAD OF THE SHORTWAVE TROUGH AS SHOWN BY THE GFS...UKMET...AND THE GFDL OR BE LEFT BEHIND AS SHOWN BY THE ECMWF AND HWRF. THE NHC DAY 5 POINT IS BETWEEN THE TWO CAMPS SHOWING A SLOW NORTHWARD MOTION. GIVEN THAT THE CYCLONE HAS FARED RATHER WELL AFTER MOVING ACROSS HAITI...AND THAT THE TRACK FORECAST HAS ONLY MINIMAL INTERACTION WITH CUBA...THE INTENSITY FORECAST AFTER 12 HOURS HAS BEEN ADJUSTED UPWARD FOLLOWING THE TREND OF THE LATEST INTENSITY GUIDANCE. ISAAC IS EXPECTED TO BECOME A HURRICANE IN ABOUT 36 HOURS...WITH ADDITIONAL INTENSIFICATION EXPECTED AS THE CYCLONE MOVES INTO THE EASTERN GULF OF MEXICO IN A FAVORABLE ENVIRONMENT. THE NEW NHC INTENSITY FORECAST IS CLOSE TO THE INTENSITY CONSENSUS AIDS THROUGH 72 HOURS AND FOLLOWS A BLEND OF THE DECAY SHIPS AND LGEM AFTERWARD. THE NEW NHC FORECAST NECESSITATES THE ISSUANCE OF A HURRICANE WARNING FOR THE FLORIDA KEYS AND A PORTION OF THE SOUTHWEST COAST OF FLORIDA AT THIS TIME. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF ISAAC DUE TO THE UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 19.0N 73.3W 50 KT 60 MPH 12H 25/1800Z 20.4N 75.0W 50 KT 60 MPH...INLAND 24H 26/0600Z 22.2N 77.6W 55 KT 65 MPH...OVER WATER 36H 26/1800Z 23.8N 80.0W 65 KT 75 MPH 48H 27/0600Z 25.0N 81.8W 70 KT 80 MPH 72H 28/0600Z 27.7N 84.9W 80 KT 90 MPH 96H 29/0600Z 30.5N 86.0W 70 KT 80 MPH...INLAND 120H 30/0600Z 32.5N 86.0W 35 KT 40 MPH...INLAND $$ FORECASTER BRENNAN |
