ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM HURRICANE HILARY DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092011 200 AM PDT SUN SEP 25 2011 CLOUD TOP TEMPERATURES AROUND THE EYE OF HILARY HAVE WARMED A BIT OVER THE PAST FEW HOURS. DVORAK CI- AND FINAL-T NUMBERS AT 06Z FROM BOTH TAFB AND SAB WERE 5.0 AND 6.0...RESPECTIVELY. LEANING TOWARD THE HIGHER END OF THE CI/FINAL-T NUMBER BLEND...THE INITIAL INTENSITY IS LOWERED TO 110 KT. THERE HAS BEEN LITTLE RECENT MICROWAVE IMAGERY TO SHOW HOW THE INNER CORE OF HILARY HAS EVOLVED...BUT IT IS POSSIBLE THAT INNER-CORE DYNAMICS SUCH AS EYEWALL REPLACEMENT CYCLES WILL RESULT IN FLUCTUATIONS IN INTENSITY OVER THE NEXT DAY OR TWO. OTHER THAN THOSE FLUCTUATIONS...GRADUAL WEAKENING IS INDICATED BY MOST OF THE INTENSITY GUIDANCE THROUGH 48 HOURS...AND THIS IS REFLECTED IN THE OFFICIAL FORECAST. LATE IN THE PERIOD...MORE RAPID WEAKENING SHOULD BEGIN AS HILARY MOVES INTO COOLER WATERS AND VERTICAL SHEAR INCREASES...ESPECIALLY AT DAYS 4 AND 5. THE NEW NHC FORECAST AT THOSE TIMES IS CLOSE TO THE LGEM MODEL. SMOOTHING THROUGH THE TROCHOIDAL WOBBLES OF THE CENTER OVER THE PAST 12 TO 18 HOURS...THE INITIAL MOTION ESTIMATE IS 275/08...AS HILARY CONTINUES TO BE STEERED BY A LARGE SUBTROPICAL RIDGE TO ITS NORTH. DURING THE FORECAST PERIOD...THE RIDGE WILL WEAKEN AS A MID/UPPER- LEVEL LOW NOW LOCATED NEAR 25N 135W MOVES EASTWARD. AS THE RIDGE WEAKENS...HILARY SHOULD SLOW DOWN AND TURN TOWARD THE WEST- NORTHWEST IN ABOUT 3 DAYS. THEN AS THE MID/UPPER-LEVEL LOW AMPLIFIES TO THE NORTHWEST OR WEST OF HILARY AT DAYS 4 AND 5...THE CYCLONE SHOULD BE DRAWN NORTHWARD OR NORTH-NORTHEASTWARD WITH SOME INCREASE IN FORWARD SPEED. THE USUALLY RELIABLE GFS AND ECMWF MODELS ARE NOW IN BETTER AGREEMENT ON THIS SCENARIO. THE NEW NHC TRACK FORECAST IS A LITTLE SOUTH OF THE PREVIOUS ONE THROUGH 48 HOURS DUE TO THE INITIAL POSITION. AT DAYS 4 AND 5 THE NHC FORECAST HAS BEEN NUDGED EASTWARD AND IS CLOSE TO THE TVCE MULTI-MODEL CONSENSUS AND A BLEND OF THE GFS AND ECMWF MODELS. THE INITIAL 34-KT WIND RADII WERE ADJUSTED INWARD BASED ON DATA FROM A 0450 UTC ASCAT PASS. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 17.0N 108.4W 110 KT 125 MPH 12H 25/1800Z 17.1N 109.7W 110 KT 125 MPH 24H 26/0600Z 17.1N 111.4W 105 KT 120 MPH 36H 26/1800Z 17.2N 113.1W 105 KT 120 MPH 48H 27/0600Z 17.3N 114.6W 100 KT 115 MPH 72H 28/0600Z 18.2N 116.4W 85 KT 100 MPH 96H 29/0600Z 20.5N 116.0W 70 KT 80 MPH 120H 30/0600Z 23.5N 115.5W 55 KT 65 MPH $$ FORECASTER BRENNAN NNNN
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