MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (NAMTHEUN) WARNING NR 06// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 15W (NAMTHEUN), LOCATED APPROXIMATELY 157 NM EAST- SOUTHEAST OF KADENA AB, HAS TRACKED NORTH-NORTHEASTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY AND A 011002Z 91 GHZ SSMIS IMAGE DEPICTS DEEP FLARING CENTRAL CONVECTION EMANATING FROM A VERY COMPACT LOW LEVEL CIRCULATION CENTER. THE INITIAL POSITION IS BASED ON RECENT RADAR DATA FROM JMA WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 65 KNOTS AND IS BASED ON PERSISTENCE IN THE CONVECTIVE STRUCTURE AND RECENT DVORAK ESTIMATES FROM ALL AGENCIES REPORTING T4.0 (65 KNOTS). UPPER-LEVEL ANALYSIS SHOWS THE PRESENCE OF A STRONG POLEWARD OUTFLOW CHANNEL INTO A TROUGH JUST OFF TO THE NORTHWEST AND COMPETING SOUTHWESTERLY FLOW WHICH IS HINDERING ANY SUBSTANTIAL EQUATORWARD OUTFLOW. SEA SURFACE TEMPERATURES ARE FAVORABLE, NEAR 30 CELSIUS, WITH HIGH OCEAN HEAT CONTENT. CURRENTLY TY 15W IS TRACKING NORTHEAST AND DEACCELERATING INTO A WEAK STEERING ENVIRONMENT AS THE NEAR-EQUATORIAL RIDGE MOVES OFF TO THE SOUTHWEST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. IN THE SHORT-TERM FORECAST TY 15W WILL REMAIN IN A WEAK STEERING ENVIRONMENT OVER THE NEXT 48 HOURS AS A DEEP-LAYERED SUBTROPICAL RIDGE TO THE NORTHEAST SLOWLY BUILDS AND GENTLY GUIDES TY 15W TO THE NORTH-NORTHWEST. INTENSIFICATION IS EXPECTED OVER THE NEXT 48 HOURS REACHING A PEAK INTENSITY OF 100 KNOTS. INTENSIFICATION IS PARTICULARLY DIFFICULT GAUGE AS WESTERLY WINDS ALOFT WILL CONTINUE TO COMPETE WITH THE STRONG POLEWARD CHANNEL INTO THE TROUGH, AND FAVORABLE WATERS WILL PERSIST. BEYOND TAU 48 THE STEERING RIDGE WILL BUILD SUFFICIENTLY TO STEER TY 15W INTO THE HIGH WIND SHEAR OF THE UPPER-LEVEL TROUGH AND BEGIN TO WEAKEN CONSIDERABLY. C. IN THE EXTENDED TAUS TY 15W WILL SHIFT BACK TO A NORTHEASTWARD TRACK AS IT ROUNDS THE RIDGE AXIS RIDING INTO THE TROUGH. LANDFALL IS EXPECTED NEAR SASEBO, JAPAN AROUND TAU 72 AS A STRONG TROPICAL STORM. THE LAND INTERACTION WILL LEAD TO FURTHER WEAKENING AND BY TAU 120 TY 15W WILL START TRANSITIONING INTO AN EXTRATROPICAL SYSTEM. DYNAMIC MODEL GUIDANCE HAS BEEN STRUGGLING DUE TO THE SMALL STRUCTURE OF THE STORM, BUT IS STARTING TO COME INTO BETTER AGREEMENT AND OVERALL SUPPORTING THE FORECAST PHILOSOPHY. NAVGEM, COAMPS-TC, AND GFDN ARE STILL SHOWING AN EARLIER TURN TO THE NORTHEAST UNREALISTICALLY ERODING THE STEERING RIDGE. DUE TO THE UNCERTAINTY AND WEAK STEERING ENVIRONMENT THERE IS LOW CONFIDENCE IN THE FORECAST TRACK.// NNNN NNNN