WDXS31 PGTW 162100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (THIRTEEN) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.1S 68.4E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 485 NM SOUTH-SOUTHWEST OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 10 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM UNDER SHEAR FROM THE EAST WITH SUSTAINED, FLARING CONVECTION OVER THE CENTER. THE INITIAL POSITION IS BASED OFF A 161720Z PARTIAL ASCAT-C IMAGE DEPICTING HALF OF A CIRCULATION WITH 25 KT WINDS ABOUT 20 NM FROM THE CENTER OF THE CIRCULATION IN THE NORTHEAST QUADRANT. THE INITIAL INTENSITY OF 35 KTS IS HEDGED SLIGHTLY HIGHER THAN THE PGTW DVORAK CURRENT INTENSITY ESTIMATE OF 2.0 (30 KTS) BUT IS IN LINE WITH FMEE AT 2.5 (35 KTS). TC 13S IS CURRENTLY IN A MARGINALLY FAVORABLE ENVIRONMENT DUE TO MODERATE VERTICAL WIND SHEAR OF 20-25 KTS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS FMEE: T2.5 - 35 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 20-25 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 13S IS FORECAST TO CONTINUE GENERALLY WESTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE TO THE SOUTH OVER THE NEXT 24 HOURS WITH MODERATE INTENSIFICATION. AFTER TAU 24, THE SYSTEM WILL HAVE REACHED 55 KTS AND BEGIN TO TURN SOUTHWESTWARD AS THE RIDGE IS DEGRADED BY A PASSING MIDLATITUDE TROUGH. IT WILL CONTINUE THIS DIRECTION, REACHING AN INTENSIFICATION OF 95 KTS BY TAU 96. AROUND THIS TIME, TC 13S WILL TURN SLIGHTLY WEST-SOUTHWESTWARD AS ANOTHER SUBTROPICAL RIDGE BUILDS TO THE SOUTH. THE SYSTEM IS EXPECTED TO BE UNDER MODERATE VERTICAL WIND SHEAR FOR MOST OF THE FORECAST THUS LIMITING PEAK INTENSIFICATION TO AROUND 95 KTS BY TAU 120. MODEL DISCUSSION: NUMERICAL MODELS ARE CURRENTLY IN GOOD AGREEMENT IN REGARDS TO TRACK FORECAST WITH ONLY A 110 NM CROSS-TRACK SPREAD AT TAU 120. THIS EXCLUDES NVGM AS AN OUTLIER WHICH TRACKS THE SYSTEM ABOUT 250 NM SOUTH OF CONSENSUS. INTENSITY GUIDANCE IS ALSO IN FAIRLY GOOD AGREEMENT WITH MOST MODELS SHOWING A PERIOD OF MODERATE INTENSIFICATION UP TO TAU 96. HOWEVER, THERE IS SOME SPREAD IN PEAK INTENSITY. FOR EXAMPLE, HWRF PEAKS AT 85 AND GFS PEAKS AT 95 KTS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN