WDXS31 PGTW 232100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) WARNING NR 014// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.7S 107.1E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 422 NM WEST-NORTHWEST OF LEARMONTH, AUSTRALIA MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 25 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WELL TO THE WEST OF FRAGMENTED AND DISORGANIZED CONVECTION. CIMSS ANALYSIS AND HWRF MODEL FIELDS SUGGEST STRONG VERTICAL WIND SHEAR (25-35 KNOTS) FROM THE WEST, WHICH IS BORN OUT BY THE SATELLITE DEPICTION. ADDITIONALLY, HWRF CROSS-SECTIONS AND ANIMATED WATER VAPOR IMAGERY SUGGESTS DRY AIR IS SMOTHERING THE SYSTEM IN THE MID-LEVELS, INHIBITING CONVECTIVE DEVELOPMENT. A 231810Z AMSR2 91GHZ MICROWAVE IMAGE DEPICTED THE LLCC TO GOOD EFFECT, WITH LOW LEVEL SPIRAL BANDING WRAPPING INTO THE TIGHTLY DEFINED LLC. THE LLCC HAS TRACKED ON A MORE WESTWARD TRACK OVER THE PAST SIX HOURS THAN WAS PREVIOUSLY ANTICIPATED. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE EXPOSED LLCC IN THE ANIMATED EIR AND SWIR IN CONJUNCTION WITH THE AMSR2 IMAGERY NOTED ABOVE. THE INITIAL INTENSITY IS HEDGED SLIGHTLY LOWER THAN THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES, MORE TOWARDS THE RAW ADT VALUES WHICH ARE DOWN TO THE 2.8 RANGE AND THE AGENCY FINAL-T VALUES OF T3.0 (45 KNOTS). INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF A LOW TO MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED OVER NORTHWEST AUSTRALIA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS APRF: T3.5 - 55 KTS CIMSS SATCON: 59 KTS AT 231528Z CIMSS ADT: 51 KTS AT 231740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 25-30 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: MID-LEVEL DRY AIR ENVELOPMENT. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. THE FORECAST HAS BEEN TRUNCATED TO 48 HOURS. FORECAST DISCUSSION: OVER THE PAST SIX HOURS THE SYSTEM HAS RAPIDLY WEAKENED UNDER THE INFLUENCE OF STRONG WESTERLY SHEAR AND DRY AIR MOVING IN FROM THE WEST AND ENVELOPING THE SYSTEM. THE RECENT MOTION VECTOR HAS BEEN TOWARDS THE WEST, AND RECENT AMSR2 MICROWAVE IMAGERY SUGGESTS THE SYSTEM MAY EVEN HAVE MOVED SLIGHTLY NORTH OF WEST SINCE 1200Z. THE NEAR-TERM MOTION VECTOR IS IN RESPONSE TO THE PRESENCE OF AN EXTENSION OF THE STR, RIDGING WEST IN THE MID-LEVELS. THIS RIDGE IS FORECAST TO RAPIDLY ERODE AND BREAK DOWN IN THE NEXT 12 HOURS, AND TC 21S IS FORECAST TO TURN SHARPLY POLEWARD AROUND TAU 12, ACCELERATING SOUTHWARD ALONG THE GRADIENT BETWEEN THE STR TO THE EAST AND A SUBTROPICAL LOW APPROACHING FROM THE WEST. AS THE SYSTEM CONTINUES TO MOVE POLEWARD, IT WILL ENCOUNTER INCREASING VWS, EVEN MORE DRY AIR AND MOVE OVER STEADILY COOLING WATERS, LEADING TO STEADY WEAKENING. BY TAU 24 THE SYSTEM WILL MOVE SOUTH OF THE 26C ISOTHERM AND BEGIN TO DIRECTLY INTERACT WITH THE SUBTROPICAL LOW MOVING IN FROM THE WEST, MARKING THE START OF SUBTROPICAL TRANSITION. NO LATER THAN TAU 48 THE SYSTEM WILL LOSE ITS TOPICAL CHARACTERISTICS AS IT MOVES UNDER THE 500MB LOW ALOFT, AND COMPLETE TRANSITION TO A GALE-FORCE SUBTROPICAL STORM. MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL TRACK SCENARIO THROUGH TAU 48. THE TAU 12 FORECAST POINT IS WELL OUTSIDE THE ENVELOPE AS A NOD TO THE RECENT MOTION VECTOR. HOWEVER, GLOBAL MODEL FIELD ANALYSIS AND THE DETERMINISTIC TRACKERS SUGGEST A SHARP TURN SHORTLY AFTER TAU 12, AND THE FORECAST TRACK CLOSES WITH, BUT REMAINS WEST OF, THE CONSENSUS MEAN THROUGH THE REMAINDER OF THE FORECAST. INTENSITY GUIDANCE IS MIXED, WITH THE DECAY SHIPS GUIDANCE SUGGEST RAPID WEAKENING TO BELOW 35 KNOTS WITH 24 HOURS, WHILE THE HWRF AND COAMPS-TC INDICATE NEAR-TERM WEAKENING FOLLOWING BY ANOTHER ROUND OF INTENSIFICATION AS THE SYSTEM TRANSITIONS TO SUBTROPICAL. THE JTWC FORECAST LIES ABOVE THE CONSENSUS THROUGH TAU 24, THEN CLOSELY FOLLOWS THE MEAN THEREAFTER. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN