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| #536999 (Received by flhurricane at: 10:47 PM 25.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 1100 PM EDT SAT AUG 25 2012 SATELLITE AND RADAR DATA FROM CUBA SHOW THAT ISAAC IS MOVING PARALLEL TO...BUT OFFSHORE OF...THE NORTHERN COAST OF CUBA. THE HURRICANE HUNTER AIRCRAFT DID NOT FIND ANY STRONGER WINDS DURING THE LATTER PORTION OF THE FLIGHT AND THE INITIAL WIND SPEED REMAINS 50 KT. HOWEVER...THUNDERSTORM ACTIVITY HAS INCREASED IN A BAND TO THE NORTH AND EAST OF THE CENTER DURING THE PAST FEW HOURS AND ISAAC MAY BE ON THE VERGE OF STRENGTHENING. THE NEXT RECONNAISSANCE FLIGHT IS EXPECTED TO BE IN THE CYCLONE AROUND 0600 UTC. THE INITIAL MOTION ESTIMATE IS 305/15 KT. ISAAC SHOULD CONTINUE ON A WEST-NORTHWESTWARD TO NORTHWESTWARD MOTION DURING THE NEXT 24 HOURS OR SO BETWEEN A LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM OVER THE NORTHWESTERN CARIBBEAN SEA AND A MID-LEVEL RIDGE OVER THE WESTERN ATLANTIC. THE MODEL GUIDANCE IS TIGHTLY CLUSTERED DURING THIS TIME AND SHOWS A TRACK OVER THE STRAITS OF FLORIDA AND NEAR OR OVER THE FLORIDA KEYS. IN ABOUT 48 HOURS...ISAAC WILL BE NEARING THE WESTERN PORTION OF THE RIDGE AND SHOULD MOVE IN A GENERAL NORTHWESTWARD HEADING OVER THE EASTERN GULF OF MEXICO...BUT LARGE DIFFERENCES EXIST BETWEEN THE LATEST ECMWF AND GFS MODELS AFTER THAT TIME. THE ECMWF RECURVES ISAAC AHEAD OF A MID-LATITUDE TROUGH OVER THE EASTERN UNITED STATES...WHILE THE GFS SLOWS ISAAC DOWN AS THE TROUGH BYPASSES THE SYSTEM AND THE MODEL THEN TURNS THE CYCLONE WESTWARD TO THE SOUTH OF A DEVELOPING MID- TO UPPER-LEVEL RIDGE. THIS BIFURCATION IS ALSO SEEN IN THE MOST RECENT ECMWF AND GFS ENSEMBLES WITH ABOUT AN EQUAL NUMBER OF MEMBERS SHOWING RECURVATURE VERSUS A CONTINUE NORTHWESTERLY TRACK TOWARD THE NORTHERN GULF COAST. SINCE THE UNCERTAINTY IS LARGE AND EITHER OF THESE SCENARIOS ARE POSSIBLE AT THIS TIME...THE NHC FORECAST IS LIES BETWEEN THEM. THE UPDATED TRACK IS VERY CLOSE TO THE PREVIOUS ADVISORY THROUGH 36 HOURS. AFTER THAT TIME...THE TRACK HAS BEEN ADJUSTED WESTWARD...BUT IT REMAINS EAST OF THE DYNAMICAL MODEL CONSENSUS TO RETAIN SOME CONTINUITY WITH THE PREVIOUS FORECAST. THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO BECOME MORE CONDUCIVE FOR STRENGTHENING DURING THE NEXT COUPLE OF DAYS AS ISAAC MOVES OVER THE WARM WATERS OF THE FLORIDA STRAITS AND EASTERN GULF. STEADY STRENGTHENING IS EXPECTED AND ISAAC IS EXPECTED TO BE AT OR NEAR HURRICANE STRENGTH WHEN THE CENTER REACHES THE FLORIDA KEYS. ADDITIONAL STRENGTHENING IS LIKELY WHILE THE CYCLONE MOVES OVER THE EASTERN GULF OF MEXICO. THE NEW INTENSITY FORECAST IS A LITTLE HIGHER THAN THE PREVIOUS ADVISORY AND IS BETWEEN THE SHIPS/LGEM GUIDANCE AND THE MORE AGGRESSIVE HWRF MODEL. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK SINCE SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER. SINCE LARGE UNCERTAINTIES REMAIN IN THE EXTENDED PORTION OF THE FORECAST...IT IS TOO EARLY TO DETERMINE EXACTLY WHERE AND WHEN ISAAC WILL MAKE LANDFALL ALONG THE GULF COAST. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 22.1N 77.2W 50 KT 60 MPH 12H 26/1200Z 23.4N 79.4W 55 KT 65 MPH 24H 27/0000Z 24.6N 81.8W 65 KT 75 MPH...NEAR FLORIDA KEYS 36H 27/1200Z 25.8N 83.7W 75 KT 85 MPH 48H 28/0000Z 27.2N 85.2W 85 KT 100 MPH 72H 29/0000Z 29.5N 86.5W 90 KT 105 MPH 96H 30/0000Z 31.5N 86.5W 50 KT 60 MPH...INLAND 120H 31/0000Z 34.0N 86.0W 25 KT 30 MPH...INLAND $$ FORECASTER BROWN |
