ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM HURRICANE HILARY DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092011 200 PM PDT WED SEP 28 2011 A NOAA HURRICANE HUNTER AIRCRAFT ON A RESEARCH MISSION HAS FOUND THAT THE MAXIMUM WINDS IN HILARY REMAIN AROUND 70 KT...BASED ON A PEAK SFMR WIND OF 68 KT AND A FLIGHT-LEVEL WIND MAXIMUM OF 82 KT. THE CENTRAL PRESSURE OF 980 MB IS BASED ON A DROPSONDE MEASUREMENT OF 982 MB WITH 17 KT OF WIND AT THE SURFACE. HILARY IS CURRENTLY MOVING ACROSS THE 26C ISOTHERM...AND THE COMBINATION OF MUCH COOLER WATERS AND INCREASING VERTICAL SHEAR WILL LEAD TO RAPID WEAKENING AS THE MID-LEVEL CIRCULATION SHEARS OFF AND LEAVES THE LOW-LEVEL CIRCULATION BEHIND OVER THE NEXT DAY OR TWO. BY 48 HOURS THE CYCLONE SHOULD BECOME A REMNANT LOW AS IT MOVES OVER SUB-23C WATERS. GLOBAL MODEL FIELDS SHOW THAT THE REMNANT LOW WILL DISSIPATE BY 96 HOURS...OR POSSIBLY SOONER. THE NHC FORECAST IS IN GOOD AGREEMENT WITH THE LGEM THROUGH DISSIPATION. THE AIRCRAFT FIXED THE CENTER A LITTLE TO THE LEFT OF THE PREVIOUS FORECAST TRACK...AND THE INITIAL MOTION ESTIMATE IS 325/07. HILARY SHOULD TURN TOWARD THE NORTH-NORTHWEST BY TONIGHT AND CONTINUE ON THAT HEADING FOR THE NEXT COUPLE OF DAYS AS IT IS PULLED NORTHWARD BY A MID-LEVEL LOW MOVING SOUTHWARD ALONG 128W. AS THE CYCLONE SHEARS APART...THE LOW-LEVEL CENTER WILL TURN TOWARD THE WEST AND THEN SOUTH OF DUE WEST ON DAYS 3 AND 4 AS IT COMES UNDER THE INFLUENCE OF THE LOW-LEVEL SUBTROPICAL RIDGE. THE TRACK GUIDANCE HAS SHIFTED AGAIN TOWARD THE WEST FOR THIS CYCLE...AND THE OFFICIAL FORECAST HAS BEEN ADJUSTED IN THAT DIRECTION. THE NHC TRACK LIES A LITTLE TO THE RIGHT OF THE MULTI-MODEL CONSENSUS THROUGH 48 HOURS AND IS A LITTLE TO THE RIGHT OF THE FASTER ECMWF MODEL AFTER THAT TIME. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 19.0N 118.9W 70 KT 80 MPH 12H 29/0600Z 19.8N 119.4W 60 KT 70 MPH 24H 29/1800Z 21.0N 120.0W 50 KT 60 MPH 36H 30/0600Z 22.1N 120.5W 40 KT 45 MPH 48H 30/1800Z 23.2N 121.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 01/1800Z 24.5N 123.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 02/1800Z 23.5N 125.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/1800Z...DISSIPATED $$ FORECASTER BRENNAN NNNN
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