WDXS31 PGTW 281500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) WARNING NR 023// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.9S 76.3E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 720 NM EAST OF PORT MATHURIN, RODRIGUES ISLAND, MAURITIUS MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 14 KTS SIGNIFICANT WAVE HEIGHT: 24 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM MAINTAINED ITS OVERALL CONVECTIVE STRUCTURE EVEN AS THE LOW LEVEL CIRCULATION (LLC) CONTINUED TO WEAKEN AND UNRAVEL. THE LLC, PREVIOUSLY FULLY EXPOSED, IS NOW BECOMING PARTIALLY OBSCURED BY RE-DEVELOPING CONVECTION ALONG THE SOUTHERN SECTORS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY- OBSCURED LLC IN THE MSI LOOP. THE INITIAL INTENSITY IS PLACED WITH HIGH CONFIDENCE BASED ON RECENT SCATTEROMETER DATA AND OVERALL ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES. ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH LOW VERTICAL WIND SHEAR AND STRONG POLEWARD OUTFLOW OFFSET BY COOLING SEA SURFACE TEMPERATURES AND DRY AIR INTRUSION IN THE LOW LEVELS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA. CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST THROUGH SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS CIMSS SATCON: 47 KTS AT 280851Z CIMSS ADT: 30 KTS AT 280915Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 5-10 KTS SST: 24-25 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC DARIAN WILL CONTINUE ON ITS CURRENT SOUTHWESTWARD TRACK UNDER THE STEERING STR. AFTER TAU 36, IT WILL BEGIN TO ROUND THE STR AXIS AND TURN MORE SOUTHWARD. THE MARGINAL ENVIRONMENT WILL MAINTAIN THE CURRENT INTENSITY UP TO TAU 48. AFTERWARD, AS THE SYSTEM CRESTS THE STR AXIS AND ACCELERATES POLEWARD, THE INCREASING VWS AND THE SST COOLING FURTHER, WILL TRIGGER GRADUAL EROSION. CONCURRENTLY BY TAU 36, THE SYSTEM WILL APPROACH THE BAROCLINIC ZONE AND BEGIN SUBTROPICAL TRANSITION AND BY TAU 72, WILL TRANSFORM INTO A SUBTROPICAL LOW. HOWEVER, THERE IS A DISTINCT POSSIBILITY THAT THE SYSTEM WILL WEAKEN TO BELOW WARNING CRITERIA BEFORE SUBTROPICAL TRANSITION. MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST. THERE IS, HOWEVER, ONLY MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST DUE TO THE DEGREE OF UNCERTAINTY ON THE IMPACT OF THE MARGINAL ENVIRONMENT POSSIBLY LEADING TO EARLY DISSIPATION. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN