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| #536594 (Received by flhurricane at: 10:56 AM 24.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1100 AM EDT FRI AUG 24 2012 RECONNAISSANCE AIRCRAFT DATA AND SATELLITE IMAGERY INDICATE THAT ISAAC HAS BECOME BETTER ORGANIZED DURING THE PAST SEVERAL HOURS. WHILE THE CIRCULATION CENTER REMAINS ELONGATED EAST-TO-WEST WITH MULTIPLE EMBEDDED VORTICITY MAXIMA...THE LARGE CENTRAL AREA OF LIGHT WINDS HAS SHRUNK AS THE STRONGEST WINDS MOVE CLOSER TO THE CENTER. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT REPORTED 66 KT FLIGHT-LEVEL WINDS AT 850 MB NORTHEAST OF THE CENTER...ALONG WITH SFMR BIAS-CORRECTED WIND ESTIMATES NEAR 50 KT. BASED ON THESE DATA...THE INITIAL INTENSITY IS INCREASED TO 50 KT. THE 12Z POSITION USED A MEAN CENTER...WHICH RESULTED IN A SOUTHWARD ADJUSTMENT. SINCE THEN...ISAAC APPEARS TO HAVE ACQUIRED A STRONGER NORTHWARD COMPONENT OF MOTION...AND THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/12. THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT THAT ISAAC SHOULD MOVED NORTHWESTWARD FOR THE NEXT 72 HR...STEERED BY THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC TOWARD A WEAKNESS IN THE RIDGE OVER THE SOUTHEASTERN UNITED STATES. THIS PART OF THE NEW FORECAST TRACK IS SHIFTED A LITTLE TO THE LEFT OF THE PREVIOUS TRACK BASED ON THE INITIAL POSITION...AND LIES NEAR THE CONSENSUS MODELS. AFTER 72 HR...THE SPREAD OF THE TRACK GUIDANCE INCREASES DUE TO MODEL DISAGREEMENT ON THE EVOLUTION OF A TROUGH OVER THE EASTERN UNITED STATES. THE ECMWF KEEPS MORE RIDGE BETWEEN ISAAC AND THE TROUGH...WHICH RESULTS IN A NORTHWESTWARD MOTION THROUGH DAY 5. THE GFS HAS A STRONGER TROUGH...WHICH RESULTS IN A MORE NORTHWARD MOTION. THE GUIDANCE ENVELOPE HAS SHIFTED A LITTLE EASTWARD AFTER 72 HR...AND THUS THE LATTER PORTION OF THE NEW FORECAST TRACK IS ALSO ADJUSTED EASTWARD. WHILE THE ORGANIZATION HAS IMPROVED...THE STRUCTURE OF ISAAC STILL DOES NOT FAVOR RAPID INTENSIFICATION DESPITE A VERY FAVORABLE UPPER-LEVEL WIND PATTERN. THE EARLY PART OF THE INTENSITY FORECAST SHOWS A LITTLE MORE STRENGTHENING THAN EARLIER...AND IT IS POSSIBLE THAT ISAAC COULD BE NEAR HURRICANE STRENGTH WHEN IT REACHES HISPANIOLA. LAND INTERACTION WILL LIMIT THE INTENSITY FROM 24-48 HR...AND THIS PART OF THE FORECAST MAY NEED SOME ADJUSTMENT AFTER IT IS SEEN WHAT STRUCTURE ISAAC HAS AFTER CROSSING HISPANIOLA. ISAAC SHOULD STRENGTHEN OVER THE GULF OF MEXICO...WITH THE FORECAST SHOWING THE CYCLONE BECOMING A HURRICANE BEFORE REACHING THE NORTHERN GULF COAST. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK 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 24/1500Z 16.3N 70.8W 50 KT 60 MPH 12H 25/0000Z 17.4N 72.6W 55 KT 65 MPH 24H 25/1200Z 19.2N 75.1W 55 KT 65 MPH 36H 26/0000Z 20.9N 77.6W 50 KT 60 MPH...INLAND 48H 26/1200Z 22.3N 79.5W 45 KT 50 MPH...INLAND 72H 27/1200Z 25.0N 83.0W 55 KT 65 MPH...OVER WATER 96H 28/1200Z 28.0N 85.5W 65 KT 75 MPH 120H 29/1200Z 31.0N 86.5W 70 KT 80 MPH...INLAND $$ FORECASTER BEVEN |
