000 WTPZ44 KNHC 270850 TCDEP4 HURRICANE HILARY DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092011 200 AM PDT TUE SEP 27 2011 HILARY IS GRADUALLY WEAKENING. WHILE THE CENTRAL CONVECTION HAS BEEN PULSING...THE EYE OF THE HURRICANE HAS RECENTLY DISAPPEARED AND THE ORGANIZATION OF THE INNER CORE CONVECTION HAS DECREASED. ALTHOUGH THE EXACT CAUSE IS UNCLEAR...INNER CORE STRUCTURAL CHANGES MAY BE RESPONSIBLE FOR RECENT DEGRADATION OF SATELLITE APPEARANCE. SUBJECTIVE INTENSITY ESTIMATES AND ADT VALUES HAVE DECREASED FURTHER SINCE 0000 UTC...AND A BLEND OF T AND CI NUMBERS IS THE BASIS FOR LOWERING THE INITIAL INTENSITY TO 100 KT. EVEN THOUGH THE VERTICAL SHEAR IS FORECAST TO REMAIN LOW THROUGH ABOUT 48 HOURS...HILARY IS ALREADY DEPARTING THE WARMEST WATERS OF THE BASIN. IN FACT...ACCORDING TO THE SHIPS MODEL...THE OCEANIC HEAT CONTENT WILL BE ABOUT HALF OF ITS CURRENT VALUE A DAY FROM NOW. INNER CORE DYNAMICS NOTWITHSTANDING...A STEADY WEAKENING IS LIKELY DURING THIS TIME. AFTER THAT...HILARY SHOULD ENCOUNTER INCREASING SOUTHWESTERLY SHEAR AND DRAMATICALLY COOLER WATERS... BOTH OF WHICH WILL RESULT IN A RAPID WEAKENING. THE OFFICIAL INTENSITY FORECAST HAS BEEN LOWERED RELATIVE TO THE PREVIOUS ONE...WITH HILARY NOW FORECAST TO BECOME A REMNANT LOW A DAY SOONER. HILARY HAS BEEN WOBBLING...BUT A SMOOTHING OF CENTER FIXES YIELDS A LONGER-TERM MOTION JUST SOUTH OF DUE WEST...265/09. GLOBAL MODELS FORECAST THE MID-LEVEL RIDGE GUIDING HILARY WESTWARD TO BREAK DOWN DURING THE NEXT 12-24 HOURS IN RESPONSE TO A TROUGH OVER THE SOUTHWESTERN UNITED STATES AND BAJA CALIFORNIA. THE MODEL GUIDANCE AGREES THAT THIS SHOULD CAUSE HILARY TO TURN SHARPLY NORTHWARD WITH A DECREASE IN FORWARD SPEED BUT DIFFERS ON HOW SOON THE TURN WILL OCCUR. THE GFS SOLUTION...AS IT HAS IN PREVIOUS CYCLES...LIES ON THE EASTERN EDGE OF THE MODEL SUITE SINCE IT BREAKS DOWN THE RIDGE SOONER. WHILE THIS OUTCOME CANNOT BE COMPLETELY DISCREDITED...IT SEEMS SOMEWHAT UNREALISTIC GIVEN THE CONTINUED STEADY MOTION TOWARD THE WEST. THE OFFICIAL FORECAST PLACES GREATER WEIGHT ON THE REMAINDER OF THE GUIDANCE WHICH DELAYS THE TURN. LATER IN THE PERIOD...LARGE-SCALE MODELS ARE IN GOOD AGREEMENT THAT HILARY WILL ROTATE AROUND AN UPPER-LEVEL LOW CURRENTLY SLIDING EASTWARD FROM 28N129W. THE DEGREE OF INTERACTION WITH THIS FEATURE WILL AT LEAST BE PARTLY DEPENDENT ON WHERE HILARY ULTIMATELY TURNS NORTHWARD. THE OFFICIAL NHC TRACK FORECAST HAS BEEN NUDGED SLIGHTLY TO THE LEFT AND IS NEAR BUT TO THE RIGHT OF THE MULTI-MODEL AND HFIP CONSENSUS AIDS. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 16.6N 115.7W 100 KT 115 MPH 12H 27/1800Z 16.8N 116.5W 100 KT 115 MPH 24H 28/0600Z 17.4N 117.1W 90 KT 105 MPH 36H 28/1800Z 18.4N 117.4W 80 KT 90 MPH 48H 29/0600Z 19.6N 117.4W 70 KT 80 MPH 72H 30/0600Z 22.1N 117.4W 50 KT 60 MPH 96H 01/0600Z 24.5N 117.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 02/0600Z 27.0N 118.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ FORECASTER KIMBERLAIN