MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (IN-FA) WARNING NR 20// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 27W (IN-FA), LOCATED APPROXIMATELY 198 NM NORTH OF YAP, HAS TRACKED WEST-NORTHWESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE SHOWS AN EXPANSION OF CONVECTIVE BANDING ALONG THE NORTHERN HALF OF THE SYSTEM. A NOTICEABLE WEAKENING OF THE POLEWARD OUTFLOW CHANNEL CAN BE OBSERVED IN THE EIR IMAGERY. OVER THE PAST 12 HOURS DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD HAVE SHOWN A SLOW WEAKENING TREND, WHICH MATCHES THE RECENT LOSS OF THE EYE, AS IT HAS BECOME CLOUD-FILLED. GIVEN THE OBSERVED WEAKENING TREND AND LOSS OF ORGANIZATION IN THE UPPER LEVEL OUTFLOW PATTERN, THE INITIAL INTENSITY HAS BEEN DECREASED TO 110 KNOTS. A MINOR INCREASE IN VERTICAL WIND SHEAR AS TY 27W TRACKS CLOSER TO THE DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH HAS STIFLED STRONGER INTENSIFICATION IN THE LAST SIX HOURS. THE STR ANCHORED TO THE NORTH REMAINS THE PRIMARY STEERING INFLUENCE, MAINTAINING THE SYSTEM ON A WEST-NORTHWESTWARD TRACK. A. THE INTENSITY TREND HAS SHIFTED FROM A MARGINAL INCREASE IN THE 12 TO 24 HOUR RANGE, TO A STEADY-STATE TREND OVER THE NEXT 12 HOURS WITH THE BEGINNING OF A WEAKENING TREND BEYOND TAU 12. THE TRACK FORECAST PHILOSOPHY REMAINS UNCHANGED. B. TY 27W IS FORECAST TO MAINTAIN A WEST-NORTHWESTWARD TRACK THROUGH TAU 36 UNDER THE STEERING INFLUENCE OF THE DEEP LAYERED STR TO THE NORTH. BEYOND THAT, THE SYSTEM WILL TRACK MORE POLEWARD AS IT ROUNDS THE SOUTHWESTERN PERIPHERY OF THE STR, AS AN APPROACHING MID- LATITUDE TROUGH CREATES A WEAKNESS ALONG THE WESTERN EXTENT OF THE STR. A STEADY INCREASE IN VWS WITH A SLOW DECREASE IN SEA SURFACE TEMPERATURES WILL START THE WEAKENING TREND OVER THE NEXT 12 TO 24 HOURS AS TY IN-FA TRACKS TO THE NORTHWEST THROUGH TAU 36. BEYOND TAU 36, AS THE TRACK TAKES A NORTHEASTERN TURN AROUND THE AXIS OF THE STR, THE ENVIRONMENTAL CONDITIONS WILL QUICKLY BECOME UNFAVORABLE, LEADING TO AN INCREASED WEAKENING TREND THROUGH TAU 72. C. IN THE EXTENDED FORECAST, TY IN-FA WILL ACCELERATE AS IT TRACKS TO THE NORTHEAST, BEGINNING TO INTERACT WITH THE MID-LATITUDE WESTERLIES. EXTRA-TROPICAL TRANSITION IS EXPECTED TO COMMENCE NEAR TAU 96. HIGH VWS IS EXPECTED TO CONTINUE TO ERODE THE SYSTEM THROUGH THE END OF THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT THROUGH TAU 120, LENDING TO HIGH CONFIDENCE TO THE JTWC TRACK FORECAST WHICH IS POSITIONED CLOSE TO THE MULTI- MODEL CONSENSUS.// NNNN NNNN