WTPA45 PHFO 240247 TCDCP5 TROPICAL STORM HILDA DISCUSSION NUMBER 7 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP112009 500 PM HST SUN AUG 23 2009 HILDA CONTINUES TO GRADUALLY INTENSIFY...DESPITE THE PRESENCE OF MODERATE...EASTERLY VERTICAL WIND SHEAR. AN ORGANIZED BAND OF DEEP CONVECTION ALONG THE SOUTHERN AND EASTERN SIDE OF HILDA HAS PERSISTED THROUGH THE DAY AND HAS RESULTED IN THE DVORAK CI NUMBERS FROM ALL THE FIX AGENCIES AND ADT TO INCREASE BY AT LEAST 0.5 IN THE PAST SIX HOURS. IN ADDITION...UW-CIMSS AMSU INTENSITY ALGORITHM HAS DETECTED A STRENGTHENING WARM CORE ALOFT. THUS...THE INITIAL INTENSITY HAS BEEN RAISED TO 50 KT. THE INITIAL MOTION IS 280/10...ESSENTIALLY UNCHANGED FROM SIX HOURS AGO. HILDA IS BEING STEERED IN A GENERAL WESTERLY DIRECTION WITHIN A DEEP EASTERLY FLOW CREATED BY AN UPPER LEVEL ANTICYCLONE TO THE NORTH ALONG 20N AND A STRONG SURFACE HIGH FARTHER NORTH. THE EASTERLY FLOW ALOFT IS CREATING MODERATE...EASTERLY VERTICAL WIND SHEAR AROUND 15 KT AND IS INHIBITING OUTFLOW ALONG THE NORTHEAST QUADRANT OF HILDA. IN SPITE OF THESE MARGINAL CONDITIONS...HILDA HAS MANAGED TO INTENSIFY TODAY. HILDA IS FORECAST TO INTENSIFY SLIGHTLY AND CONTINUE ON A TRACK THAT IS JUST NORTH OF DUE WEST THROUGH THE NEXT 48 HOURS AS RIDGING AT THE SURFACE AND ALOFT REMAINS TO THE NORTH. THE FORECAST TRACK IS ESSENTIALLY DOWN THE MIDDLE OF A TIGHTLY CLUSTERED GUIDANCE ENVELOPE DURING THE FIRST 36 HOURS AND IS ALONG THE NORTHERN PORTION OF THE ENVELOPE BY 48 HOURS. WITH SST VALUES HOVERING AROUND 27C AND WINDS ALOFT CHANGING LITTLE...A GRADUAL INTENSIFICATION TREND IS FORECAST TO PERSIST THROUGH 48 HOURS. THE FORECAST INTENSIFIES HILDA SLIGHTLY FASTER THAN THE PREVIOUS PACKAGE AND FOLLOWS ICON RELATIVELY CLOSELY. BY 72 HOURS...THE TRACK OF HILDA SHIFTS TO THE DUE WEST AS RIDGING ALOFT STRENGTHENS OVER AND TO THE WEST OF THE HAWAIIAN ISLANDS AS A DEEP UPPER TROUGH DIGS FAR EAST OF THE ISLANDS BETWEEN 150W AND 140W. THE DYNAMIC MODELS AND SHIPS FORECAST THE WIND SHEAR TO SHIFT MORE NORTHERLY BUT RELAX SLIGHTLY AT THIS TIME. DUE TO THE UNCERTAINTY OF THESE EFFECTS...THE FORECAST INTENSIFICATION HAS BEEN HALTED AFTER 48 HOURS...WITH HILDA REMAINING AT A HIGH END TROPICAL STORM. HOWEVER...IT WOULD NOT BE SURPRISING IF HILDA INTENSIFIES FURTHER AFTER 48 HOURS AND BECOMES A HURRICANE AS A GOOD NUMBER OF THE INTENSITY MODELS PREDICT. THE TRACK FORECAST AT 72 HOURS AND BEYOND IS SLIGHTLY TO THE RIGHT OF AN INCREASINGLY DIVERGENT GUIDANCE ENVELOPE. FORECAST POSITIONS AND MAX WINDS INITIAL 24/0300Z 14.2N 143.2W 50 KT 12HR VT 24/1200Z 14.6N 144.6W 50 KT 24HR VT 25/0000Z 15.0N 146.7W 55 KT 36HR VT 25/1200Z 15.3N 148.7W 55 KT 48HR VT 26/0000Z 15.4N 150.7W 60 KT 72HR VT 27/0000Z 15.3N 154.2W 60 KT 96HR VT 28/0000Z 15.2N 156.9W 60 KT 120HR VT 29/0000Z 15.0N 160.0W 60 KT $$ FORECASTER WROE