MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 31W (YUTU) WARNING NR 24// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON (STY) 31W (YUTU), LOCATED APPROXIMATELY 571 NM NORTH-NORTHWEST OF YAP, HAS TRACKED WESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) WHICH SHOWS A ROUND 28-NM EYE, SURROUNDED BY SYMMETRIC DEEP CONVECTION. THE MICROWAVE EYE FEATURE IN A 270537Z SSMI 37 GHZ CHANNEL IS SLIGHTLY SOUTH OF THE EYE FEATURE IN THE 85 GHZ CHANNEL, SUGGESTING THE CYCLONE IS TILTED SLIGHTLY TO THE NORTH WITH HEIGHT. THE INITIAL INTENSITY OF 135 KNOTS IS AVERAGED BETWEEN MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T6.5-T7.0 (127-140 KNOTS). THE ENVIRONMENT IS MARGINALLY FAVORABLE WITH GOOD EQUATORWARD OUTFLOW, EXCELLENT POLEWARD OUTFLOW, AND WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURE BEING OFFSET BY HIGH (25 KNOTS) VERTICAL WIND SHEAR (VWS). THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR) TO THE NORTH WITH AN EASTWARD MOVING MID-LATITUDE TROUGH CREATING A WEAKNESS IN THE STR TO THE NORTH OF STY 31W. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THROUGH TAU 72, STY 31W IS FORECAST TO CONTINUE TRACKING WESTWARD TO WEST-SOUTHWESTWARD AND GRADUALLY WEAKEN THANKS TO DIMINISHING OUTFLOW AS THE TROPICAL CYCLONE AND MID-LATITUDE TROUGH TO THE NORTH MOVE FURTHER APART. BY TAU 72, STY 31W IS EXPECTED TO MAKE LANDFALL ON LUZON. MOST OF THE NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT (177 NM SPREAD) WITH THE JTWC TRACK FORECAST, HOWEVER, THE SPREAD INCREASES TO ABOUT 300 NM WHEN CONSIDERING THE NORTHERN (COAMPS-GFS) AND SOUTHERN (JGSM) OUTLIERS. BASED ON THE SPREAD, THERE IS MODERATE UNCERTAINTY IN THE JTWC TRACK FORECAST. C. BEYOND TAU 72, AN APPROACHING MID-LATITUDE TROUGH WILL CREATE A WEAKNESS IN THE STR AND ALLOW STY 31W TO BEGIN RECURVING NORTHWARD. ENVIRONMENTAL CONDITIONS WILL BE GENERALLY UNFAVORABLE FOR THIS PORTION OF THE FORECAST AND THAT, COUPLED WITH LAND INTERACTION, IS EXPECTED TO WEAKEN STY 31W. THERE IS A CHANCE THAT ENHANCED POLEWARD OUTFLOW AS IT ROUNDS THE STR MAY ALLOW FOR SLIGHT INTENSIFICATION BEFORE HIGH VWS CAUSES STY 31W TO WEAKEN. SPREAD IN THE NUMERICAL MODELS IS ALMOST 1000 NM BY TAU 120, ALTHOUGH THE SPREAD IS REDUCED TO 230 NM WHEN COAMPS-GFS AND JGSM ARE REMOVED. BASED ON THE RELATIVELY SMALL SPREAD IN THE BULK OF THE GUIDANCE, THERE IS MODERATE UNCERTAINTY IN THE EXTENDED PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN