WTPA42 PHFO 090908 TCDCP2 HURRICANE FELICIA DISCUSSION NUMBER 23 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP082009 1100 PM HST SAT AUG 08 2009 HURRICANE FELICIA APPEARS TO BE WEAKENING BASED ON THE LATEST SATELLITE IMAGERY...MICROWAVE DATA AND HURRICANE RECONNAISSANCE AIRCRAFT DATA. THE LATEST AIRCRAFT FIX AT 0729 UTC INDICATED THE CENTRAL PRESSURE HAD FILLED TO 990 MB. THE HIGHEST FLIGHT-LEVEL WINDS WERE 80 KT IN THE NORTHEAST QUADRANT AT 700 MB AROUND 0600 UTC. THERE WERE ALSO SFMR WINDS FOR THE SURFACE OF UP TO 69 KT AROUND THE SAME TIME. A DROPSONDE IN THE NORTHEAST EYEWALL ALSO INDICATED THE AVERAGE LOW-LEVEL WINDS ADJUSTED TO THE SURFACE ARE NEAR 63-68 KT. THESE AIRCRAFT DATA...ALONG WITH DVORAK CI NUMBERS OF 4.0...INDICATE THAT FELICIA HAS WEAKENED TO 70 KT FOR THIS ADVISORY. CONSIDERABLE WARMING OF THE CLOUD TOPS HAS OCCURRED IN THE PAST FEW HOURS ACCORDING TO THE INFRARED SATELLITE IMAGERY. DATA FROM SEVERAL SATELLITES WITH MICROWAVE DATA FROM AROUND 0300 UTC INDICATED THE DEEPEST CONVECTION WAS STARTING TO BE DISPLACED TO THE NORTHEAST OF THE APPARENT CENTER...WHICH MAY SUGGEST INCREASING VERTICAL WIND SHEAR IS STARTING TO AFFECT THE HURRICANE. THE CURRENT MOTION OF FELICIA IS 280/13...WHICH IS CLOSE TO THE PREVIOUS 12 HOUR MOTION. SOME OF THE MODELS FORECAST FELICIA TO GAIN A LITTLE MORE LATITUDE BEFORE TURNING DUE WEST...WHILE MOST OF THE OTHERS CALL FOR THE HURRICANE TO MOVE AT 270 DEGREES WITHIN 12 TO 24. BEYOND 24 HOURS OR SO...ALL OF THE MODEL GUIDANCE AGREES ON A DUE WESTWARD HEADING ALONG THE SOUTHERN PERIPHERY OF A LOW- TO MID-LEVEL RIDGE...WITH TRACKS CROSSING THE MAIN HAWAII ISLANDS AT VARYING LATITUDES. THE LATEST OFFICIAL TRACK FORECAST CONTINUES DOWN THE CENTER OF THE GUIDANCE ENVELOPE. THERE WAS A SLIGHT NORTHWARD ADJUSTMENT THROUGH THE FIRST 36 HOURS FROM THE PREVIOUS ADVISORY. THE FORWARD MOTION OF THE SYSTEM WAS ALSO SLOWED SLIGHTLY BEYOND 36 HOURS...SINCE THE GUIDANCE WAS QUITE A BIT SLOWER AT THAT TIME. NOTE THAT THERE ARE A NUMBER OF VERY RELIABLE MODELS ON EITHER SIDE OF THE OFFICIAL FORECAST. THEREFORE...THE CENTER OF FELICIA COULD PASS OVER ANY PORTION OF THE MAIN HAWAIIAN ISLANDS DURING THE NEXT 2-3 DAYS. FELICIA APPEARS TO HAVE BEGUN THE EXPECTED WEAKENING TREND. THE UNDERLYING SEA-SURFACE TEMPERATURES REMAIN NEAR ABOUT 25 CELSIUS...BUT THESE VALUES WILL GRADUALLY WARM ALONG THE FORECAST TRACK THROUGHOUT THE FIVE-DAY FORECAST PERIOD. HOWEVER...WESTERLY VERTICAL WIND SHEAR HAS INCREASED TO NEAR 10 KT...AND IS FORECAST TO INCREASE TO GREATER THAN 20 KT WITHIN 12 TO 24 HOURS. THIS IS ABOUT THE TIME FELICIA IS ON THE DOORSTEP OF THE HAWAIIAN ISLANDS. THE INTENSITY GUIDANCE MODELS RESPOND TO THESE FACTORS BY FORECASTING GRADUAL WEAKENING...BUT ALL OF THEM HOLD ON TO A TROPICAL STORM THROUGH 36 HOURS...AND SOME EVEN TO 72 HOURS. THE NEW OFFICIAL FORECAST INTENSITY IS ADJUSTED SLIGHTLY DOWN FROM THE PREVIOUS ONE TO BE CONSISTENT WITH THE INTENSITY CONSENSUS...ICON. GIVEN THE UNCERTAINTIES WITH INTENSITY FORECASTING...IT IS IMPORTANT TO POINT OUT THE INTENSITY PROBABILITIES ACCOMPANYING THIS ADVISORY PACKAGE. THAT PRODUCT INDICATES THAT THERE IS ABOUT A 20 PERCENT CHANCE OF FELICIA BEING A TROPICAL STORM IN 48 HOURS WHEN IT IS VERY NEAR THE HAWAIIAN ISLANDS AND ABOUT A 45 PERCENT CHANCE OF IT BEING A TROPICAL DEPRESSION. THERE IS A CHANCE THAT A TROPICAL STORM WARNING MAY BE NEEDED FOR PARTS OF THE WATCH AREA SUNDAY MORNING...SINCE THE LEAD TIME FOR WARNINGS IN THE CENTRAL PACIFIC BASIN IS 36 HOURS. FORECAST POSITIONS AND MAX WINDS INITIAL 09/0900Z 20.3N 144.7W 70 KT 12HR VT 09/1800Z 20.7N 146.8W 60 KT 24HR VT 10/0600Z 20.8N 149.4W 55 KT 36HR VT 10/1800Z 20.8N 152.0W 50 KT 48HR VT 11/0600Z 20.6N 154.6W 40 KT 72HR VT 12/0600Z 20.7N 159.4W 30 KT 96HR VT 13/0600Z 21.1N 164.3W 25 KT 120HR VT 14/0600Z 21.9N 168.9W 25 KT...DISSIPATING $$ FORECASTER HOUSTON/WROE