MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (KROSA) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 11W (KROSA), LOCATED APPROXIMATELY 174 NM SOUTH- SOUTHWEST OF IWO TO, HAS TRACKED NORTHWESTWARD AT 03 KNOTS (KTS) OVER THE PAST SIX HOURS. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION BASED ON A PARTIALLY OBSCURED EYE FEATURE IN ANIMATED MULTISPECTRAL SATELLITE IMAGERY. ANIMATED ENHANCED INFRARED IMAGERY REVEALS THAT DEEP CONVECTION IS PRESENT IN 50 TO 75 PERCENT OF THE EYEWALL AND THAT IS LIKELY INHIBITING THE EYE FROM BECOMING WELL FORMED. THE INITIAL INTENSITY OF 75 KTS IS CONSISTENT WITH DVORAK FIX INTENSITY ESTIMATES FROM KNES, RJTD, AND PGTW OF T4.5 (77 KTS). WARM (29-30C) SEA SURFACE TEMPERATURE, GOOD EQUATORWARD AND POLEWARD OUTFLOW CHANNELS, AND LOW (10-15 KT) VERTICAL WIND SHEAR MAKE THE ENVIRONMENT FAVORABLE FOR INTENSIFICATION. AN INDUCED TROUGH TO THE NORTH IS CAUSING SUBSIDENCE AHEAD OF THE CYCLONE THAT IS LIKELY OFFSETTING THE OTHERWISE VERY FAVORABLE ENVIRONMENT. TY 11W IS TRACKING SLOWLY ALONG THE PERIPHERY OF SUBTROPICAL RIDGING STRETCHING AROUND TO THE NORTH, EAST, AND SOUTH. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THROUGH TAU 72, TY 11W IS EXPECTED TO MEANDER ON A REVERSE S PATTERN UNDER THE COMPLEX STEERING ENVIRONMENT. THIS TRACK WILL KEEP THE SYSTEM NEAR IWO TO FOR THE DURATION OF THIS PORTION OF THE FORECAST. BY TAU 72, THE SUBTROPICAL RIDGE (STR) WILL REORIENT SUFFICIENTLY TO ALLOW THE SYSTEM TO MOVE NORTHWARD AT AROUND 7 KTS. THE SOMEWHAT FAVORABLE ENVIRONMENT WILL ALLOW SOME INTENSIFICATION TO 80 KTS BY TAU 12, HOWEVER, THE ENVIRONMENT WILL REMAIN MARIGNAL OVERALL AND THE INTENSITY IS EXPECTED TO REMAIN NEAR STEADY STATE THROUGH THIS PORTION OF THE FORECAST. NUMERICAL MODELS GENERALLY AGREE WITH THE SHAPE OF THE TRACK. NOTABLY, THERE IS A CLUSTER OF MEMBERS (ECMWF, GALWEM, AND UKMET) ON THE WESTERN SIDE OF THE ENVELOPE OF SOLUTIONS. THE CURRENT TRACK FORECAST IS HEDGED WEST OF THE CONSENSUS TO FAVOR THAT CLUSTER WITH FAIR CONFIDENCE DUE TO THE SPREAD. C. ALTHOUGH THE WESTERN CLUSTER REMAINS, MODEL GUIDANCE CONTINUES TO SPREAD IN THE EXTENDED FORECAST. ADDITIONALLY, OVERALL DETERIORATING ENVIRONMENTAL CONDITIONS ARE EXPECTED TO GRADUALLY REDUCE INTENSITY TO 60 KTS BY TAU 120. THE TRACK FORECAST REMAINS COMPLEX ALTHOUGH THE GUIDANCE TENDS TO AGREE THAT RIDGING TO THE NORTH OF THE SYSTEM WILL WEAKEN IN THE NEAR TERM IN RESPONSE TO A DEVELOPING MID-LATITUDE TROUGH. IN THE EXTENDED PERIOD, THE WESTERN CLUSTER INDICATES THAT, IN THE WAKE OF THE TROUGH, A RIDGE WILL BUILD TO THE NORTH OF TY 11W AND TAKE OVER AS THE DOMINANT STEERING MECHANISM. THE WESTERN CLUSTER APPEARS MORE PROBABLE AND THE JTWC TRACK FORECAST CONTINUES TO BE HEDGED WEST OF THE CONSENSUS. GIVEN THE SPREAD IS 390 NM AT TAU 120, CONFIDENCE IN THE JTWC TRACK FORECAST IS LOW FOR THE EXTENDED PERIOD. // NNNN NNNN