MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 31W (YUTU) WARNING NR 12// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON (STY) 31W (YUTU), LOCATED APPROXIMATELY 109 NM SOUTHEAST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A 20 NM WIDE ROUND EYE, SURROUNDED BY SYMMETRIC DEEP CONVECTION WITH BANDS OF EXTREMELY DEEP CONVECTION TO THE NORTH AND SOUTH. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN THE EIR IMAGERY. COMPARING THE 36 AND 89 GHZ CHANNELS IN A 240354Z AMSR2 MICROWAVE PASS REVEALS THE EYE IS TILTED SLIGHTLY TO THE NORTHEAST WITH HEIGHT. THIS IS ACCOUNTED FOR IN THE INITIAL POSITION. THE INITIAL INTENSITY OF 145 KNOTS IS BETWEEN DVORAK CURRENT INTENSITY ESTIMATES FROM KNES AND RJTD OF T7.0 (140 KTS) AND PGTW OF T7.5 (155 KTS). THE ENVIRONMENT REMAINS FAVORABLE WITH MODERATE (15-20 KNOT) VERTICAL WIND SHEAR (VWS), EXCELLENT RADIAL OUTFLOW, AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURE. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THE STR TO THE NORTHEAST IS EXPECTED TO CONTINUE STEERING STY 31W NORTHWESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 72. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE FOR CONTINUED GRADUAL INTENSIFICATION THROUGH TAU 24, STEADY INTENSITY THROUGH TAU 48, AND GRADUAL WEAKENING DUE TO HIGH VWS BY TAU 72. THE NUMERICAL MODEL TRACKERS REMAIN IN GOOD AGREEMENT THROUGH TAU 24 BEFORE OUTLIERS START TO DEVELOP TO THE NORTH (COAMPS-GFS AND NAVGEM) AND SOUTH (UKMET, GALWEM, AND JGSM). THE SPREAD IS 275 NM BY TAU 72, THEREFORE UNCERTAINTY IS HIGH FOR THIS PORTION OF THE FORECAST. C. BEYOND TAU 72, STY 31W IS FORECASTED TO BEGIN TURNING SLOWLY AROUND THE STR AXIS WHILE CONTINUING TO WEAKEN. IN THE EXTENDED PERIOD, THE GUIDANCE ENVELOPE IS HUGE WITH OVER 1000 NM OF SPREAD BETWEEN THE NORTHERN AND SOUTHERN OUTLIERS. THERE ARE THREE CLUSTERS IN THE GUIDANCE. THE SOUTHERN CLUSTER CONSISTS OF THE UKMET, GALWEM, AND JGSM AND PREDICTS A WESTWARD TO WEST-SOUTHWESTWARD TRACK, PRIMARILY DUE TO A STR TO THE NORTHWEST. THE NORTHERN CLUSTER CONSISTS OF NAVGEM AND COAMPS-GFS AND PREDICTS RECURVATURE DUE TO AN APPROACHING MID-LATITUDE TROUGH PRIOR TO TAU 72. THE MIDDLE CLUSTER CONSISTS OF ECMWF, GFS, HWRF, AND THE ECMWF AND GFS ENSEMBLE MEANS. FOR THE MOST PART, THIS CLUSTER PREDICTS A SLIGHT NORTHWARD TURN BY TAU 120 AS A SECOND MID-LATITUDE TROUGH CREATES A WEAKNESS IN THE STR. MOST MEMBERS OF THE ECMWF ENSEMBLE SUGGEST THE MIDDLE CLUSTER IS THE MOST PLAUSIBLE SCENARIO. THE JTWC FORECAST TRACK FOLLOWS THE MIDDLE CLUSTER. UNCERTAINTY IS VERY HIGH FOR THE EXTENDED PORTION OF THE JTWC FORECAST.// NNNN NNNN