WTPA45 PHFO 252051 TCDCP5 TROPICAL STORM HILDA DISCUSSION NUMBER 14 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP112009 1100 AM HST TUE AUG 25 2009 HILDA HAS BEEN STRUGGLING THIS MORNING AND THE MOST RECENT INFRARED IMAGES SHOW WARMING CLOUD TOPS OVER THE CENTER AND THE DEEPEST CONVECTION CONFINED TO THE SYSTEM/S SOUTHERN QUADRANT. HILDA/S PROBLEMS MAY BE DUE TO THE INGESTION OF DRIER AIR FROM THE SURROUNDING AIRMASS. THIS IS SUGGESTED BY WATER VAPOR IMAGES...SATELLITE SOUNDER PRECIPITABLE WATER DATA AND THE PRESENCE OF OUTFLOW BOUNDARIES IN THE EARLY MORNING VISIBLE IMAGES PUSHING OUT FROM BENEATH THE HIGH LEVEL CLOUDS. SSMI 37 GHZ DATA FROM 1632 UTC SHOWED THE CENTER TO BE DISPLACED FARTHER SOUTH THAN PREVIOUS POSITIONS. THIS IS SUPPORTED BY LOW CLOUDS LINES IN THE VISIBLE IMAGES. AS A RESULT...THE INITIAL POSITION HAS BEEN ADJUSTED SOUTH. DVORAK INTENSITY ESTIMATES RANGED FROM 65 KT TO 45 KT. CIMSS 1600 UTC SATCON CAME IN AT 35 KT. A QUIKSCAT PASS FROM AROUND 1600 UTC SHOWED 40 KT WINDS IN THE NORTHWEST QUADRANT. BASED ON A BLEND OF THE SUBJECTIVE AND OBJECTIVE ESTIMATES...WILL GO WITH AN INITIAL INTENSITY OF 45 KT THOUGH THIS MAY BE A BIT HIGH. HILDA HAS BEEN MOVING SOUTH OF THE SUBTROPICAL RIDGE. THE ORIENTATION OF THE MID-LEVEL RIDGE HAS RESULTED IN A MORE NORTHERLY COMPONENT IN THE STEERING FLOW THUS THE MOTION HAS BEEN TOWARD THE WEST-SOUTHWEST. GLOBAL MODELS INDICATE THIS PATTERN SHOULD CONTINUE OVER THE NEXT 48 HOURS. BEYOND 48 HOURS...A MID- AND UPPER LEVEL TROUGH IS EXPECTED TO DEVELOP NORTHWEST OF HILDA WHICH SHOULD RESULT IN A TURN TOWARD THE WEST-NORTHWEST. OBJECTIVE AIDS ARE IN BETTER AGREEMENT THAN YESTERDAY WITH MOST OF THE KEY DYNAMICAL MODELS CLUSTERED RELATIVELY TIGHT. NOGAPS IS THE NORTHERN OUTLIER BUT HAS A LESS DRASTIC NORTHWEST TURN THAN BEFORE AND KEEPS HILDA SOUTHWEST OF THE HAWAIIAN ISLANDS. THE OFFICIAL FORECAST STAYS CLOSE TO THE DYNAMICAL CONSENSUS AND HAS BEEN SHIFTED SOUTH FROM THE PREVIOUS FORECAST...MAINLY DUE TO THE SHIFT IN INITIAL POSITION. THE INTENSITY FORECAST IS PROBLEMATIC. ASIDE FROM POSSIBLE DRY AIR IMPACTS...HILDA IS IN A MILD SHEAR ENVIRONMENT WITH MORE THAN ADEQUATE SST/S. IF THE DRY AIR INFLUENCE EASES...STRENGTHENING SHOULD OCCUR AT LEAST THROUGH 72 HOURS. BEYOND 72 HOURS...GLOBAL MODELS INDICATE AN INCREASE IN VERTICAL SHEAR WHICH SHOULD WEAKEN HILDA. SHIPS...HWRF AND GHMI ALL INDICATE ADDITIONAL STRENGTHENING. THUS...THE KEY UNCERTAINTIES INCLUDE THE CONTINUED INFLUENCE OF DRY AIR AND THE STRENGTH OF VERTICAL SHEAR BEYOND DAY 3. FOR NOW...THE OFFICIAL FORECAST CALLS FOR SLIGHT WEAKENING OVER THE NEXT 24 HOURS FOLLOWED BY STRENGTHENING TO 72 HOURS. WEAKENING IS FORECAST BEYOND 72 HOURS DUE TO SHEAR EFFECTS. NEEDLESS TO SAY...THERE IS NOT A LOT OF CONFIDENCE IN THIS INTENSITY FORECAST. FORECAST POSITIONS AND MAX WINDS INITIAL 25/2100Z 14.1N 149.1W 45 KT 12HR VT 26/0600Z 13.8N 150.3W 40 KT 24HR VT 26/1800Z 13.3N 151.9W 40 KT 36HR VT 27/0600Z 13.0N 153.5W 45 KT 48HR VT 27/1800Z 13.0N 155.1W 50 KT 72HR VT 28/1800Z 13.6N 158.8W 60 KT 96HR VT 29/1800Z 14.5N 163.0W 60 KT 120HR VT 30/1800Z 16.1N 167.3W 55 KT $$ FORECASTER KODAMA