MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (TRAMI) WARNING NR 21// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 28W (TRAMI), LOCATED APPROXIMATELY 377 NM SOUTH OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS THE CENTRAL CONVECTION HAS SIGNIFICANTLY WEAKENED AS EVIDENCED BY RAPIDLY WARMING CLOUD TOPS. ADDITIONALLY, FEEDER BANDS HAVE BEGUN TO UNRAVEL. HOWEVER, THE SYSTEM HAS MAINTAINED A WELL-DEFINED 32 NM EYE WHERE THE INITIAL POSITION IS BASED ON WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 115 KNOTS IS BASED ON EQUIVALENT PGTW AND RJTD DVORAK CURRENT INTENSITY ESTIMATES OF T6.0/115 KNOTS. THE UPPER LEVEL ENVIRONMENT REMAINS GENERALLY FAVORABLE WITH LOW VERTICAL WIND SHEAR (VWS) AND GOOD RADIAL OUTFLOW. HOWEVER, DRY AIR ASSOCIATED WITH AN APPROACHING SHORT WAVE TROUGH OVER JAPAN IS NOW IMPACTING THE NORTHWESTERN SIDE OF THE CYCLONE. TY 28W IS DRIFTING SLOWLY NORTHWARD ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) THAT RECEDED TO THE EAST AND WEAKENED BY THE SHORTWAVE TROUGH. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 28W IS FORECAST TO CONTINUE ITS SLOW NORTHWARD DRIFT OR MAY BECOME QUASI-STATIONARY DUE TO THE WEAK STEERING ENVIRONMENT. AFTER TAU 24, THE STR WILL RE-BUILD AND DRIVE THE CYCLONE NORTHWESTWARD THROUGH TAU 72. THE WEAKENING TREND - DUE TO THE SUBSIDING EFFECT OF THE SHORT WAVE TROUGH - WILL CONTINUE IN THE NEAR TERM AND REDUCE THE SYSTEM TO 95 KNOTS. HOWEVER, AFTER TAU 48, AS THE CYCLONE MOVES AWAY FROM ITS COLD WAKE, THE OCEAN HEAT CONTENT IS EXPECTED TO INCREASE; PLUS, POLEWARD OUTFLOW WILL SURGE, FUELING A SECONDARY INTENSIFICATION PHASE. THE NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT WITH JGSM AS THE SOLE OUTLIER TO THE LEFT OF THE ENVELOPE. HOWEVER, THERE REMAINS SIGNIFICANT DIFFERENCES IN THE TRACK SPEED AND TIMING OF THE NORTHWESTWARD TRACK. IN VIEW OF THESE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST. C. AFTER TAU 72, TY TRAMI IS FORECAST TO RECURVE AND ACCELERATE NORTHEASTWARD AS IT ROUNDS THE STR AXIS AND BEGINS INTERACTING WITH THE MID-LATITUDE WESTERLIES. BY TAU 120, TY 28W WILL REACH THE SOUTHERN TIP OF KYUSHU, JAPAN. THE SECONDARY INTENSIFICATION PHASE WILL CONTINUE AND BRING THE SYSTEM TO 110 KNOTS BY TAU 96. AFTERWARD, INCREASING VERTICAL WIND SHEAR AND INTERACTION WITH THE JAPANESE ISLANDS WILL GRADUALLY ERODE THE SYSTEM. BY TAU 120, AT 95 KNOTS, THE CYCLONE WILL ALSO BEGIN EXTRA-TROPICAL TRANSITION. THE NUMERICAL MODEL ENVELOPE IS AT ITS NARROWEST IN THE EXTENDED PORTION OF THE FORECAST; HOWEVER, GIVEN THE INITIAL TRACK UNCERTAINTY, CONFIDENCE IN THE JTWC LATTER TAU TRACK FORECAST REMAINS LOW.// NNNN NNNN