WDXS31 PGTW 271500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) WARNING NR 021// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.7S 81.9E INITIAL INTENSITY: 80 KTS GEOGRAPHIC REFERENCE: 886 NM SOUTHEAST OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 32 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM CONTINUED TO WEAKEN AS EVIDENCED BY WARMING CLOUD TOPS AND UNRAVELING FEEDER BANDS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A RECENTLY CLOUD-FILLED EYE FEATURE IN THE EIR LOOP. THE INITIAL INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE AVERAGE OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND REFLECTS THE STEADY WEAKENING. ANALYSIS INDICATES THE ENVIRONMENT HAS BECOME UNFAVORABLE AS INCREASING VERTICAL WIND SHEAR AND COOLING SEA SURFACE TEMPERATURE HAVE OFFSET THE STRONG POLEWARD OUTFLOW. INITIAL WIND RADII BASIS: PERSISTENCE. CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST THROUGH SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS FMEE: T5.0 - 90 KTS FIMP: T4.5 - 77 KTS CIMSS SATCON: 87 KTS AT 270819Z CIMSS ADT: 75 KTS AT 271145Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 15-20 KTS SST: 25-26 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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 DARIAN WILL CONTINUE ON ITS CURRENT SOUTHWESTWARD TRACK UNDER THE STEERING STR. AFTER TAU 72, IT WILL BEGIN TO ROUND THE STR AXIS AND TURN MORE SOUTHWARD. THE UNFAVORABLE ENVIRONMENT WILL GET WORSE AS SSTS CONTINUE TO DECREASE AND VWS INCREASE, LEADING TO CONTINUED EROSION. BY TAU 96, THE CYCLONE WILL BE REDUCED TO 40KTS. CONCURRENTLY BY TAU 48, THE SYSTEM WILL APPROACH THE BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION AND BY TAU 96, WILL TRANSFORM INTO A GALE-FORCE COLD CORE LOW. MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST. THERE IS MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST UP TO TAU 72 THEN LOW CONFIDENCE AFTERWARD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN