WDPN31 PGTW 081500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (BOPHA) WARNING NR 52// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 26W (BOPHA), LOCATED APPROXIMATELY 215 NM NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED EAST-NORTHEASTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY INDICATES THAT TY 26W HAS WEAKENED RAPIDLY OVER THE PAST SIX HOURS WITH THE MAJORITY OF THE DEEP CONVECTION SHEARED EAST OF A PARTIALLY- EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). A 081134Z SSMIS IMAGE DEPICTS CURVED, SHALLOW BANDING WRAPPING INTO THE LLCC, WHICH IS POSITIONED JUST WEST OF AN ISOLATED BAND OF DEEP CONVECTION. THERE IS FAIR CONFIDENCE IN THE INITIAL POSITION BASED ON THE SSMIS IMAGE. DESPITE THE RAPID WEAKENING TREND, DVORAK CURRENT INTENSITY ESTIMATES REMAIN AT TYPHOON STRENGTH, RANGING FROM 90 TO 102 KNOTS. THE INITIAL INTENSITY IS ASSESSED AT 85 KNOTS, SLIGHTLY LOWER THAN THE DVORAK CURRENT INTENSITY ESTIMATES, BASED ON THE WEAK DEEP CONVECTIVE BANDING. TY 26W HAS MAINTAINED GOOD POLEWARD OUTFLOW; HOWEVER, THE SYSTEM REMAINS EMBEDDED IN STRONG (30 TO 40 KNOTS) WESTERLY VERTICAL WIND SHEAR (VWS). TY 26W HAS CONTINUED TO TURN EASTWARD AS IT TRACKS ALONG THE NORTHWEST PERIPHERY OF THE DEEP SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE; HOWEVER, FORECAST INTENSITY HAS BEEN DECREASED THROUGHOUT THE FORECAST PERIOD WITH DISSIPATION EXPECTED BY TAU 96. B. TY 26W WILL CONTINUE TO TRACK EASTWARD OVER THE NEXT 24 HOURS UNDER THE STEERING INFLUENCE OF THE STR BUT IS EXPECTED TO WEAKEN RAPIDLY DUE TO STRONG VWS AND SOME INTERACTION WITH LUZON. THEREAFTER, AS THE CYCLONE CONTINUES TO WEAKEN, IT IS EXPECTED TO MOVE EQUATORWARD AND WESTWARD FOLLOWING THE LOW LEVEL FLOW. THE DYNAMIC AIDS, WITH THE EXCEPTION OF WBAR AND GFS, ARE IN GOOD AGREEMENT WITH THE TRACK FORECAST THROUGH TAU 72. WBAR AND GFS ARE CONSIDERED HIGHLY UNREALISTIC SINCE THEY BOTH TRACK THE SYSTEM INTO A ZONE OF HIGH VWS ASSOCIATED WITH STRONG UPPER-LEVEL WESTERLIES AND A STRONG NORTHEAST SURGE. ANALYSIS OF GFS 850MB VORTICITY FIELDS SHOWS RAPID WEAKENING OF THE SYSTEM WEST OF LUZON AND A QUICK TURN SOUTHWARD; THE GFS VORTEX TRACKER APPEARS TO BE ERRONEOUSLY JUMPING THE CENTER EASTWARD TO ANOTHER VORTICITY MAXIMUM ASSOCIATED WITH A SHEAR LINE POSITIONED EAST OF LUZON. GIVEN THE SPREAD IN THE MODEL TRACK GUIDANCE AND HIGH TRACK DEPENDENCE ON THE INTENSITY, FORECAST CONFIDENCE THROUGH TAU 72 REMAINS LOW. C. AFTER TAU 72, TY 26W IS EXPECTED TO CONTINUE TRACKING SOUTHWESTWARD UNDER THE INFLUENCE OF LOW-LEVEL NORTHEASTERLY FLOW AND WEAKEN DUE TO ONGOING VWS AND DRY AIR ENTRAINMENT. THERE IS CONSIDERABLE UNCERTAINTY IN THE EXTENDED TRACK FORECAST GIVEN THE EXPECTED LOOPING MOTION AND A SPREAD IN ALONG-TRACK FORECAST SPEEDS AMONG CONSENSUS MODEL MEMBERS. EXTENDED FORECAST TRACK CONFIDENCE REMAINS LOW.// NNNN