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| #462433 (Received by flhurricane at: 10:53 PM 27.Sep.2011) TCDAT1 TROPICAL DEPRESSION OPHELIA DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 1100 PM AST TUE SEP 27 2011 FROM THE BIG PICTURE...OPHELIA APPEARS TO BE REASONABLY WELL ORGANIZED WITH AN EXPANDING OUTFLOW PATTERN AND A ROUND BALL OF DEEP CONVECTION NEAR THE APPARENT CENTER. HOWEVER...THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT DATA SHOW A MUCH DIFFERENT PERSPECTIVE WITH THE LOW-LEVEL CIRCULATION ELONGATED FROM EAST-NORTHEAST TO WEST-SOUTHWEST...AND PEAK SFMR VALUES OF ONLY ABOUT 29 KT. THE INITIAL WINDS ARE SET TO 30 KT IN ACCORDANCE WITH THE SFMR ESTIMATES. THE INTENSITY FORECAST IS A CHALLENGING ONE THIS EVENING. WHILE THE CURRENT OUTFLOW PATTERN WOULD SEEM TO FAVOR SIGNIFICANT INTENSIFICATION...WATER VAPOR IMAGES SHOW AN UPPER-LEVEL TROUGH OVER THE WESTERN ATLANTIC MOVING EASTWARD TOWARD THE TROPICAL CYCLONE. THIS TROUGH SHOULD SOON RAISE THE SHEAR NEAR OPHELIA... AND SINCE THE CYCLONE HAS A RATHER POOR INITIAL LOW-LEVEL STRUCTURE...ONLY A SLOW INCREASE IN WINDS IS FORECAST FOR THE FIRST DAY OR SO. THEREAFTER...THE TROUGH SHOULD WEAKEN AS AN UPPER HIGH BUILDS CLOSER TO THE TROPICAL CYCLONE...WHICH COULD SUPPORT A FASTER INTENSIFICATION. IT IS INTERESTING TO NOTE THAT THE STATISTICAL GUIDANCE IS CONSIDERABLY LOWER THAN THE LAST RUN...SHOWING OPHELIA ONLY BECOMING A MODERATE TROPICAL STORM BECAUSE OF MUCH HIGHER FORECAST SHEAR. SOME OF THIS CHANGE MIGHT BE DUE TO THE INTERPOLATED OLD OFFICIAL FORECAST WHICH IS A GOOD DEAL FASTER THAN THE GFS...AND IN THIS CASE INTRODUCES SOME ARTIFICIAL SHEAR AS IT IS CLOSER TO THE STRONG UPPER-LEVEL WINDS. I HAVE ELECTED NOT TO CHANGE THE PREVIOUS FORECAST PEAK INTENSITY GIVEN THE GFDL/HWRF STILL SHOWING CATEGORY 2 HURRICANE STATUS...BUT THE TREND IN THESE STATISTICAL MODELS SHOULD BE WATCHED. MICROWAVE AND AIRCRAFT DATA SUGGEST THE CENTER...SUCH AS IT IS...HAS REFORMED TO THE NORTHEAST...A BIT CLOSER TO THE MID-LEVEL CENTER. A LONG-TERM MOTION ESTIMATE IS 305/3...BUT THIS IS HIGHLY UNCERTAIN. OPHELIA IS EXPECTED TO MOVE A BIT FASTER TO THE NORTHWEST BY EARLY THURSDAY AS IT IS STEERED AROUND THE SOUTHWESTERN PORTION OF A STRENGTHENING SUBTROPICAL RIDGE. A TURN TO THE NORTH AND NORTHEAST SHOULD OCCUR BY THE WEEKEND DUE TO A LARGE MID-LATITUDE TROUGH DIVING OFFSHORE OF THE EASTERN UNITED STATES. THE MODEL GUIDANCE IS IN BETTER AGREEMENT THAN SIX HOURS AGO...ALTHOUGH THE SPEED DIFFERENCES ARE SIGNIFICANT. THE NHC FORECAST IS ADJUSTED EAST OF THE PREVIOUS ONE FOR THE FIRST COUPLE OF DAYS TO ACCOUNT FOR THE CENTER REPOSITIONING...AND IS VERY CLOSE TO THE TRACK AFTER THAT TIME...A BIT FASTER THAN THE MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 18.4N 59.5W 30 KT 35 MPH 12H 28/1200Z 18.8N 59.8W 35 KT 40 MPH 24H 29/0000Z 19.5N 60.2W 40 KT 45 MPH 36H 29/1200Z 20.9N 60.9W 45 KT 50 MPH 48H 30/0000Z 22.4N 61.6W 55 KT 65 MPH 72H 01/0000Z 26.3N 62.7W 65 KT 75 MPH 96H 02/0000Z 32.0N 61.5W 75 KT 85 MPH 120H 03/0000Z 40.0N 57.5W 70 KT 80 MPH $$ FORECASTER BLAKE |
