000 WTNT44 KNHC 240250 TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1100 PM AST THU AUG 23 2012 OBSERVATIONS FROM A NOAA HURRICANE HUNTER AIRCRAFT SUGGEST THAT ISAAC HAS STRENGTHENED ONLY SLIGHTLY THIS EVENING. FLIGHT-LEVEL AND SFMR-OBSERVED SURFACE WINDS FROM THE AIRCRAFT SUGGEST THAT THE CURRENT INTENSITY IS NEAR 40 KT. THE STORM CONTINUES TO HAVE FAIRLY STRONG UPPER-LEVEL OUTFLOW AND...IF THE INNER CORE BECOMES BETTER DEFINED...HAS AN OPPORTUNITY TO STRENGTHEN AS LONG AS IT REMAINS OVER WATER. HOWEVER...THE CENTER OF THE STORM IS FORECAST TO MOVE OVER SOUTHWESTERN HISPANIOLA IN 12 HOURS OR SO...AND THIS WOULD HALT ANY INTENSIFICATION. A LITTLE LATER ON...LAND INTERACTIONS WITH EASTERN CUBA WOULD ALSO INHIBIT INTENSIFICATION OR CAUSE WEAKENING. ISAAC WILL LIKELY RESTRENGTHEN WHEN IT MOVES OVER THE STRAITS OF FLORIDA AND THE EASTERN GULF OF MEXICO IN THE LATTER PART OF THE FORECAST PERIOD. HOWEVER IT SHOULD BE NOTED THAT THERE IS SIGNIFICANT UNCERTAINTY IN TROPICAL CYCLONE INTENSITY PREDICTIONS AT 3-5 DAYS. THE INITIAL MOTION ESTIMATE IS 290/16. A MID-TROPOSPHERIC TROUGH OVER THE SOUTHEASTERN U.S. IS CAUSING A BREAK IN THE SUBTROPICAL RIDGE. IN RESPONSE TO THIS...ISAAC SHOULD TURN TOWARD A MORE NORTHWESTWARD HEADING OVER THE NEXT FEW DAYS. THE MODEL CONSENSUS HAS SHIFTED A BIT TO THE RIGHT DURING THE FIRST HALF OF THE FORECAST PERIOD...PRIMARILY DUE TO AN EASTWARD SHIFT OF THE LATEST GFS TRACK. THE OFFICIAL FORECAST IS NUDGED A BIT TO THE RIGHT OF THE PREVIOUS ONE AND IS SOMEWHAT FASTER BASED ON THE LATEST MODEL GUIDANCE. THE INITIAL AND FORECAST WIND RADII HAVE BEEN EXPANDED BASED ON BUOY AND SHIP DATA. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK BECAUSE OF FORECAST UNCERTAINTIES AND THE FACT THAT ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. A SYNOPTIC SURVEILLANCE MISSION BY THE NOAA G-IV JET AIRCRAFT HAS BEEN CONDUCTED TO COLLECT ATMOSPHERIC OBSERVATIONS IN THE LARGE-SCALE ENVIRONMENT OF ISAAC. THESE DATA WILL BE ASSIMILATED INTO THE 0000 UTC RUNS OF THE GLOBAL MODELS...AND SHOULD IMPROVE THE ACCURACY OF THEIR FORECASTS FOR THE NEXT ADVISORY CYCLE. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 16.7N 68.7W 40 KT 45 MPH 12H 24/1200Z 17.5N 70.7W 55 KT 65 MPH 24H 25/0000Z 18.8N 73.1W 45 KT 50 MPH 36H 25/1200Z 20.2N 75.4W 45 KT 50 MPH...INLAND 48H 26/0000Z 21.8N 77.7W 45 KT 50 MPH...INLAND 72H 27/0000Z 24.8N 82.0W 55 KT 65 MPH...OVER WATER 96H 28/0000Z 27.5N 85.5W 70 KT 80 MPH 120H 29/0000Z 30.0N 88.0W 80 KT 90 MPH $$ FORECASTER PASCH