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| #536286 (Received by flhurricane at: 5:02 AM 23.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 500 AM AST THU AUG 23 2012 AN AIR FORCE RECONNAISSANCE AIRCRAFT INVESTIGATING ISAAC THIS MORNING HAS FOUND A POORLY DEFINED INNER CORE WITH A LARGE AREA OF LIGHT WINDS AROUND A CENTER...WHICH IS SIMILAR TO WHAT AN EARLIER NOAA RESEARCH MISSION INDICATED. RADAR DATA FROM GUADELOUPE AND SAN JUAN ALSO INDICATE A POORLY DEFINED INNER CORE CONVECTIVE PATTERN. RATHER THAN INITIALIZE THE CENTER OF ISAAC WELL TO THE SOUTH OF THE PREVIOUS TRACK...I HAVE OPTED TO USE A BLEND OF THE RECON FIXES... SATELLITE IMAGERY...DATA FROM NEARBY NOAA BUOY 42060...AND A 06Z CONSENSUS FORECAST POSITION FROM THE GFS...ECMWF...AND UKMET MODELS. THE INITIAL INTENSITY WAS ALSO DECREASED TO 35 KT BASED ON DATA FROM THE RECON AIRCRAFT AND NOAA BUOY 42060. THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 270/12 KT. THE 00Z GFS...ECMWF...AND UKMET MODELS DID AN OUTSTANDING JOB PREDICTING THE RECENT SOUTHWESTWARD JOG OR REFORMATION OF THE CENTER OF ISAAC. THOSE SAME MODELS ARE ALSO FORECASTING ISAAC TO MAKE A SHARP JOG TO THE NORTHWEST OVER THE NEXT 12-24 HOURS...AND THEN STEADY OFF ON A GENERAL WEST-NORTHWESTWARD MOTION THROUGH 48 HOURS. AFTER THAT... THE GLOBAL AND REGIONAL MODELS HAVE COME INTO BETTER AGREEMENT ON ISAAC MOVING NORTHWESTWARD TOWARD A BREAK IN THE SUBTROPICAL RIDGE THAT IS FORECAST TO DEVELOP AFTER 72 HOURS ACROSS FLORIDA AND THE EASTERN GULF OF MEXICO. THE ECMWF MODEL HAS CONTINUED ITS EASTWARD SHIFT OVER THE PAST 36 HOURS...AND EVEN THE LATEST NOGAPS AND CANADIAN MODEL RUNS HAVE SHIFTED WELL TO THE WEST ACROSS THE FLORIDA PENINSULA ARE NOW NO LONGER CONSIDERED TO BE OUTLIERS. DUE TO LESS SPREAD IN THE LATEST NHC MODEL GUIDANCE...AND THE FACT THAT ECMWF HAS SHIFTED CLOSER TO THE PREVIOUS FORECAST AT DAYS 4 AND 5...THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS ADVISORY TRACK...AND IS CLOSE TO THE DYNAMICAL CONSENSUS MODELS TVCA AND TV15. UPPER-AIR DATA FROM ST. MAARTEN AT 00Z CONFIRMS THE DRY AIR IN THE MID-LEVELS OF THE ATMOSPHERE BETWEEN 600 AND 300 MB AS ALLUDED TO IN PREVIOUS DISCUSSIONS. THIS LAYER OF VERY DRY AIR HAS BEEN HINDERING CONVECTIVE DEVELOPMENT IN THE NORTHEASTERN QUADRANT FOR THE PAST 3-4 DAYS. HOWEVER...THE GLOBAL MODELS ARE IN GOOD AGREEMENT ON THE DRY AIR MIXING OUT OVER THE NEXT 36 HOURS AND THE INNER CORE BECOMING QUITE MOIST...WHICH SHOULD ALLOW FOR SOME STEADY INTENSIFICATION TO OCCUR BEFORE ISAAC INTERACTS WITH THE MOUNTAINOUS TERRAIN OF HISPANIOLA. GIVEN THE IMPRESSIVE UPPER-LEVEL OUTFLOW PATTERN THAT THE CYCLONE HAS DEVELOPED...ISAAC IS STILL EXPECTED TO BECOME A HURRICANE BY 36 HOURS. AFTER THAT...HOWEVER... THE THE PRIMARY IMPEDIMENT TO STRENGTHENING WILL BE THE INTERACTION WITH THE LAND MASSES OF HISPANIOLA AND EASTERN CUBA. HOW MUCH THE INNER CORE OF ISAAC IS DISRUPTED WHILE OVER LAND WILL DETERMINE JUST HOW MUCH RE-STRENGTHENING WILL OCCUR ONCE THE CENTER MOVES BACK OVER WATER AFTER 72 HOURS. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND IS IN REASONABLE AGREEMENT WITH THE DECAY-SHIPS AND LGEM INTENSITY MODELS. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 15.3N 64.0W 35 KT 40 MPH 12H 23/1800Z 16.2N 65.9W 40 KT 45 MPH 24H 24/0600Z 16.9N 68.4W 50 KT 60 MPH 36H 24/1800Z 17.8N 71.1W 65 KT 75 MPH 48H 25/0600Z 19.1N 73.4W 55 KT 65 MPH 72H 26/0600Z 21.8N 77.4W 60 KT 70 MPH...INLAND 96H 27/0600Z 24.4N 80.9W 65 KT 75 MPH...OVER WATER 120H 28/0600Z 27.4N 83.7W 70 KT 80 MPH $$ FORECASTER STEWART |
