000 WTPZ44 KNHC 262040 TCDEP4 HURRICANE HILARY DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092011 200 PM PDT MON SEP 26 2011 HILARY HAS CONTINUED TO STRENGTHEN OVER THE PAST FEW HOURS...WITH AN EXPANDING AREA OF COLD CLOUD TOPS AROUND A MORE DISTINCT 10 NM WIDE EYE SEEN IN RECENT VISIBLE IMAGERY. THE INITIAL INTENSITY IS INCREASED TO 115 KT BASED ON FINAL-T NUMBERS FROM TAFB AND SAB ALONG WITH THE LATEST UW-CIMSS ADT ESTIMATES. OTHER THAN CONTINUING FLUCTUATIONS DUE TO INNER-CORE DYNAMICS...ALL OF THE GUIDANCE SHOWS SLOW WEAKENING OVER THE NEXT COUPLE OF DAYS AS HILARY MOVES OVER GRADUALLY COOLING WATERS. HILARY SHOULD BE ACROSS THE 26C ISOTHERM BY 72 HOURS...AND RAPID WEAKENING IS EXPECTED AFTER THAT TIME AS VERTICAL WIND SHEAR ASSOCIATED WITH A MID-LEVEL LOW INCREASES OVER THE CYCLONE. THE NHC FORECAST IS CLOSE TO A BLEND OF THE SHIPS AND LGEM MODELS THROUGH THE PERIOD. THE INITIAL MOTION ESTIMATE IS 265/09...AS THE HURRICANE HAS BEEN MOVING JUST SOUTH OF DUE WEST FOR THE PAST SEVERAL HOURS...PERHAPS IN RESPONSE TO AN UPPER-LEVEL ANTICYCLONE SEEN IN WATER VAPOR IMAGERY LOCATED TO THE WEST-SOUTHWEST OF HILARY. A SLOWER WESTWARD MOTION IS EXPECTED DURING THE NEXT 24 HOURS FOLLOWED BY A SHARP TURN TOWARD THE NORTH BY 48 HOURS AS THE MID-LEVEL RIDGE NORTH OF HILARY BREAKS DOWN. THROUGH THIS TIME THE NHC FORECAST HAS BEEN ADJUSTED A BIT TO THE LEFT DUE TO THE INITIAL POSITION AND MOTION AND IS CLOSE TO THE TVCE CONSENSUS. AFTER THAT TIME THE INTERACTION OF HILARY WITH A MID-LEVEL LOW CURRENTLY NEAR 27N 132W WILL BE CRITICAL TO THE TRACK OF THE CYCLONE. ALL OF THE GLOBAL MODELS SHOW THE MID-LEVEL LOW AMPLIFYING AND MOVING SOUTHEASTWARD TO A POSITION WEST OF HILARY BY 72 HOURS. HOWEVER...AND THE USUALLY RELIABLE GFS AND ECMWF MODELS REPRESENT TWO DISTINCT SCENARIOS FROM THAT TIME ONWARD. THE GFS TURNS HILARY QUICKLY NORTHEASTWARD BY 72 HOURS AND INTERACTS LESS WITH THE MID-LEVEL LOW...RESULTING IN A MORE NORTHWARD TRACK TOWARD THE BAJA PENINSULA BY DAY 5. CONVERSELY... THE ECMWF MOVES HILARY CLOSER TO THE UPPER-LEVEL LOW...RESULTING IN MORE INTERACTION AND HILARY TURNING SHARPLY NORTHWESTWARD BY DAY 5. GIVEN THIS INCREASING SPREAD IN THE GUIDANCE AND THE PLAUSIBILITY OF BOTH SCENARIOS...THE NHC FORECAST SPLITS THE DIFFERENCE AT DAYS 3 THROUGH 5 AND SHOWS A SLOW NORTHWARD MOTION. THIS FORECAST IS CLOSE TO BUT SLOWER THAN THE PREVIOUS NHC TRACK AND LIES A LITTLE EAST OF THE TVCE CONSENSUS AND TO THE WEST OF THE GFS ENSEMBLE MEAN. GIVEN THE HIGH DEGREE OF UNCERTAINTY IN THE TRACK FORECAST LATE IN THE PERIOD...IT IS IMPORTANT TO NOTE THAT AT DAYS 4 AND 5 THE AVERAGE ERROR OF THE OFFICIAL TRACK FORECAST IN THE EAST PACIFIC BASIN IS 175 TO 225 MILES. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 16.6N 114.0W 115 KT 135 MPH 12H 27/0600Z 16.7N 115.1W 110 KT 125 MPH 24H 27/1800Z 16.8N 116.1W 105 KT 120 MPH 36H 28/0600Z 17.5N 116.7W 95 KT 110 MPH 48H 28/1800Z 18.4N 116.8W 90 KT 105 MPH 72H 29/1800Z 21.0N 116.5W 70 KT 80 MPH 96H 30/1800Z 23.5N 116.5W 45 KT 50 MPH 120H 01/1800Z 26.0N 117.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER BRENNAN