WDXS31 PGTW 230900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.1S 108.2E INITIAL INTENSITY: 70 KTS GEOGRAPHIC REFERENCE: 383 NM WEST-NORTHWEST OF LEARMONTH, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 30 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A GRADUALLY WEAKENING SYSTEM AS EVIDENCED BY WARMING CENTRAL CONVECTION AND UNRAVELING FEEDER BANDS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE USING LOW CLOUD, RAIN BAND TRACING IN THE ANIMATED MULTISPECTRAL SATELLITE IMAGERY. THE INITIAL INTENSITY OF 70KTS IS ALSO ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AVERAGE OF AGENCY AND AUTOMATED DVORAK ESTIMATES (SEE BELOW). 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: SCATTEROMETER DATA. CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS CIMSS ADT: 67 KTS AT 230540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 20-25 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC CHARLOTTE WILL CONTINUE SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR. AFTER TAU 12, IT WILL BEGIN TO ROUND THE STR AXIS AND TRACK MORE SOUTHWARD THEN SOUTHEASTWARD ON THE POLEWARD SIDE OF THE STR. THE ENVIRONMENT IS EXPECTED TO BECOME MORE UNFAVORABLE WITH INCREASING VWS AND COOLING SST, LEADING TO A GRADUAL DETERIORATION. CONCURRENTLY BY TAU 48, THE SYSTEM WILL BEGIN SUBTROPICAL TRANSITION AND BY TAU 72 WILL TRANSFORM INTO A GALE-FORCE, 35-KNOT SUBTROPICAL SYSTEM WITH AN EXPANDING WIND FIELD. MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT UP TO TAU 48; AFTERWARD, THEY ERRATICALLY SPREAD OUT WITH THE MAJORITY INDICATING A REVERSAL IN THE STORM MOTION. IN VIEW OF THIS, THERE IS ONLY MEDIUM CONFIDENCE IN THE JTWC TRACK FORECAST THAT IS LAID CLOSE TO THE MODEL CONSENSUS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN