WDXS31 PGTW 230300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) WARNING NR 011// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.3S 108.9E INITIAL INTENSITY: 75 KTS GEOGRAPHIC REFERENCE: 378 NM NORTHWEST OF LEARMONTH, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 26 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MEDIUM-SIZED SYSTEM WITH DEEP CENTRAL CONVECTION REMAINING ON THE SOUTH SIDE OF THE THE LOW-LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE MSI LOOP AND EXTRAPOLATION FROM A 230115Z GMI 37GHZ IMAGE. THE INITIAL INTENSITY OF 75KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON MULTIPLE AGENCY DVORAK FIXES, EACH SHOWING A DECREASING TREND ALONG WITH THE ADVANCED DVORAK TECHNIQUE (ADT). ANALYSIS INDICATES A MARGINALLY UNFAVORABLE ENVIRONMENT WITH STRONG POLEWARD OUTFLOW AND WARM SST OFFSET BY MODERATE TO STRONG VERTICAL WIND SHEAR. THE CYCLONE IS TRACKING ALONG THE NORTHWEST PERIPHERY OF THE STR TO THE SOUTHEAST. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS APRF: T4.5 - 77 KTS CIMSS ADT: 75 KTS AT 230140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC CHARLOTTE REMAINS UNDER THE INFLUENCE OF THE STR TO THE SOUTHEAST AS IT CONTINUES TO ROUND THE STR AXIS. TC 21S WILL STAY ON A SOUTHWEST TRACK THROUGH TAU 36, THEN ROUND THE STR AXIS AND TRACK SOUTHERLY UNTIL TAU 60, WHEN IT BEGINS TO ENCROACH UPON COOLER WATERS AND ENHANCED VWS FROM AN UPPER-LEVEL TROUGH. THE APPROACHING TROUGH WILL BEGIN TO INFLUENCE THE OVERALL TRACK MOTION TOWARDS THE AUSTRALIAN COAST NEAR PERTH THROUGH THE REMAINDER OF THE FORECAST. NEARING TAU 60 AND BEFORE TAU 72, TC 21S WILL BEGIN TRANSITIONING INTO A SUBTROPICAL SYSTEM. AT TAU 96, TC CHARLOTTE WILL COMPLETE TRANSFORMATION INTO A GALE FORCED SUBTROPICAL SYSTEM WITH AN EXPANDING WIND FIELD BEFORE IT NEARS THE AUSTRALIAN COAST. MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT OVERALL UNTIL TAU 48. THE TRACK GUIDANCE BEGINS TO DIVERGE SIGNIFICANTLY ONCE TC 21S BEGINS THE SUBTROPICAL TRANSITION. NEAR TAU 60, THE MODELING GUIDANCE DEPICTS ERRATIC MOTION WITH THE STORMS ALONG-TRACK AND CROSS-TRACK SPREAD. DUE TO THIS UNCERTAINTY, THE OVERALL JTWC TRACK AND INTENSITY GUIDANCE IS MEDIUM UP TO TAU 48 AND LOW THEREAFTER. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN