MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (NAMTHEUN) WARNING NR 07// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 15W (NAMTHEUN), LOCATED APPROXIMATELY 161 NM EAST OF KADENA AB, HAS TRACKED NORTH-NORTHEASTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS BANDING CONVECTION WRAPPING INTO A SMALL AND COMPACT SYSTEM WITH AN EYE FEATURE STARTING TO EMERGE. RECENT RADAR DATA FROM JMA SHOWS THE HIGH RESOLUTION CIRCULATION CENTER LENDING HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 70 KNOTS AND IS BASED ON IMPROVEMENT IN THE CONVECTIVE STRUCTURE AND RECENT DVORAK ESTIMATES FROM ALL AGENCIES REPORTING THE CURRENT INTENSITY RANGING BETWEEN T4.0 TO T4.5 (65 TO 77 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, HOWEVER THE FORECAST TRACK REFLECTS A FASTER TRACK SPEED WITH A SLIGHTLY SHARPER TURN TO THE NORTHEAST. B. IN THE SHORT-TERM FORECAST TY 15W WILL REMAIN IN A SOMEWHAT WEAK STEERING ENVIRONMENT OVER THE NEXT 36 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 36 HOURS REACHING A PEAK INTENSITY OF 90 KNOTS. INTENSIFICATION IS PARTICULARLY DIFFICULT TO GAUGE AS WESTERLY WINDS ALOFT WILL CONTINUE TO COMPETE WITH THE STRONG POLEWARD CHANNEL INTO THE TROUGH, AND FAVORABLE WATERS WILL PERSIST. AROUND TAU 36 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. SHORTLY AFTER TAU 48 LANDFALL IS EXPECTED WITH AN ACCOMPANIED CHANGE OF TRACK TO THE NORTHEAST. C. IN THE EXTENDED TAUS TY 15W WILL CONTINUE NORTHEAST UNDER THE INFLUENCE OF THE TROUGH FURTHER WEAKENING THE SYSTEM. TY 15W IS EXPECTED TO START TRANSITIONING INTO AN EXTRATROPICAL SYSTEM AROUND TAU 96, BECOMING FULLY EXTRATROPICAL BY TAU 120. DYNAMIC MODEL GUIDANCE IS IMPROVING SOMEWHAT, SHOWING TIGHTER GROUPING IN TRACKS THROUGH TAU 72 AS IT MAKES LANDFALL AND TURNS NORTHEAST. THE 12Z ECMFW SOLUTION WAS SHOWING A FASTER TRACK THAN EACH OF THE OTHER 12Z SOLUTIONS. THE BULK OF THE 18Z SOLUTIONS HAVE SPED UP NEARLY MATCHING THE INTERPOLATED ECMWF SOLUTION. THE FORECAST TRACK REFLECTS THE INCREASE IN SPEED AND CONSEQUENTLY A SLIGHTLY TIGHTER TURN TO THE NORTHEAST. WHILE UNCERTAINTY STILL REMAINS, THERE IS GOOD CONFIDENCE IN THE FORECAST TRACK.// NNNN NNNN