MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (KROSA) WARNING NR 017// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 11W (KROSA), LOCATED APPROXIMATELY 150 NM SOUTH OF IWO TO, JAPAN, HAS TRACKED NORTHWARD AT 01 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS DECAYING DEEP CONVECTION OVER THE CORE AND NORTHWEST QUADRANT DUE TO THE PRESENCE OF CYCLONIC FLOW AND CONVERGENCE ALOFT. HOWEVER, STRONG DIFFLUENCE OVER THE EASTERN AND SOUTHERN FLANK CONTINUE TO FUEL DEEP CONVECTIVE BANDING, WHICH IS WRAPPING TIGHTLY INTO THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 092017Z SSMIS 37GHZ IMAGE INDICATES TIGHTLY-CURVED BANDING WRAPPING INTO A DEFINED LLCC, WHICH SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 75 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF 4.5 (77 KNOTS) FROM RJTD AND PGTW. WITH THE EXCEPTION OF THE COMPLEX, MARGINALLY-FAVORABLE OUTFLOW, VERTICAL WIND SHEAR AND SST VALUES REMAIN FAVORABLE. TY 11W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT WITH A NORTH-SOUTH SUBTROPICAL RIDGE POSITIONED TO THE EAST, A WEAK STR OVER WESTERN JAPAN AND A BREAK TO THE NORTH. THEREFORE, TY 11W IS TRACKING SLOWLY POLEWARD (AND ERRATICALLY). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. IN THE NEXT 72 HOURS, THE PRIMARY STEERING FOR TY 11W WILL GRADUALLY TRANSITION TO THE BUILDING STR TO THE NORTH OF TY 11W AND THE TRACK WILL SLOWLY SHIFT NORTHWESTWARD TOWARD JAPAN, PASSING SOUTHWEST OF IWO TO AROUND TAU 36. SLIGHTLY DIMINISHED OUTFLOW, WEAK SUBSIDENCE AND POSSIBLE UPWELLING COOLER WATER WILL MAKE THE ENVIRONMENT SOMEWHAT UNFAVORABLE THROUGH TAU 48 WITH GRADUAL WEAKENING TO ABOUT 60 KNOTS. AFTER TAU 48, AS THE SYSTEM BEGINS TO ACCELERATE WEST-NORTHWESTWARD TO NORTHWESTWARD OVER WARM SST, SLIGHT INTENSIFICATION IS EXPECTED. C. AFTER TAU 72, TY 11W WILL RECURVE POLEWARD ALONG THE SOUTHWEST PERIPHERY OF THE STR, WHICH IS EXPECTED TO WEAKEN AND REORIENT WITH THE APPROACH OF A DEEP MIDLATITUDE SHORTWAVE TROUGH. TY 11W SHOULD RE-INTENSIFY TO A PEAK INTENSITY OF 70 KNOTS AS POLEWARD OUTFLOW IMPROVES. SST VALUES WILL REMAIN CONDUCIVE (28-29C) DURING THIS EXTENDED PERIOD. NUMERICAL MODEL GUIDANCE DIVERGES SLIGHTLY BUT REMAINS IN GOOD AGREEMENT WITH A 125NM SPREAD IN SOLUTIONS AT TAU 120. BASED ON THE ERRATIC SHORT-TERM MOTION AND UNCERTAINTY IN THE LATER TAUS, THERE IS OVERALL MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN