MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (KAMMURI) WARNING NR 06// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 17W (KAMMURI), LOCATED APPROXIMATELY 383 NM SOUTHEAST OF IWO TO, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY CONTINUES TO DEPICT A VERY LARGE CYCLONE, SPANNING OVER 700 NM, WITH MONSOON DEPRESSION CHARACTERISTICS - WEAK CIRCULATION CENTER WITH MINIMAL CONVECTION AND DEEP CONVECTIVE BANDS IN THE OUTER PERIPHERY. THE INITIAL POSITION IS BASED ON THE EIR LOOP AND EXTRAPOLATED FROM A RAGGED WARM SPOT ON A 251546Z HIGH FREQUENCY NPP MICROWAVE PASS. THE INITIAL INTENSITY IS AVERAGED FROM DVORAK ESTIMATES FROM PGTW AND RJTD AND EXTRAPOLATED FROM A RECENT SCATTEROMETRY PASS SHOWING THE RADIUS OF STRONGER WINDS OVER 2 DEGREES AWAY FROM THE CENTER. UPPER-LEVEL ANALYSIS CONTINUES TO INDICATE THE SYSTEM IS LOCATED IN A FAVORABLE ENVIRONMENT WITH LOW (05 TO 10 KNOT) VERTICAL WIND SHEAR (VWS) AND EXCELLENT OUTFLOW CHANNELS AS EVIDENT IN THE WATER VAPOR IMAGERY. TS 17W IS CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A MID- TO DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THE STR WILL REMAIN THE DOMINANT STEERING MECHANISM FOR TS 17W THROUGH TAU 72. TS KAMMURI IS FORECAST TO TURN POLEWARD AFTER TAU 48 AS IT ROUNDS THE STR AXIS AND BEGINS TO RE-CURVE AHEAD OF AN APPROACHING MID-LATITUDE SHORTWAVE TROUGH. IN ADDITION TO THE WARM SEA SURFACE TEMPERATURES (SSTS), FAVORABLE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO PERSIST ALLOWING TS 17W TO INTENSIFY LEADING TO A PEAK INTENSITY OF 65 KNOTS BY TAU 48. C. BEYOND TAU 72, TS 17W IS FORECAST TO ACCELERATE NORTHEASTWARD AND BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS THE SYSTEM INTERACTS WITH THE MID-LATITUDE WESTERLIES BY TAU 72. THE CYCLONE WILL BECOME A STORM-FORCE COLD CORE LOW BY TAU 120. ADDITIONALLY, INCREASING VWS AND COOLING SSTS WILL CAUSE A STEADY DECAY. AVAILABLE MODEL GUIDANCE HAS IMPROVED OVER THE PAST SIX HOURS; HOWEVER, DUE TO UNCERTAINTY OF THE TRACK SPEEDS IN THE SHORT-TERM AND LARGE SPREAD AMONG MODEL TRACKERS AT THE TURN, THE CONFIDENCE IN JTWC FORECAST TRACK REMAINS LOW.// NNNN NNNN