WDPS33 PGTW 082100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12P (TWELVE) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 15.6S 163.8E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 288 NM WEST-NORTHWEST OF PORT VILA, VANUATU MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE (TC) 12P (TWELVE) BECOME SLIGHTLY DECOUPLED FROM THE PRIMARY CONVECTIVE STRUCTURE, AS INITIAL MOVEMENT OF THE LOW-LEVEL CIRCULATION CENTER (LLCC) HAS TRACKED SLOWLY TO THE EAST OVER THE LAST SIX HOURS. NORTHWESTERLY SHEAR HAS MAINTAINED ITS INFLUENCE OVER THE VERTICAL STRUCTURE OF TC 12P, AS THE VORTEX REMAINS TILTED (SOUTHEASTWARD WITH HEIGHT) FROM THE PREVIOUS ANALYSIS. THE LATEST EIR CONTINUES TO SHOW A STRUGGLING AND SHEARED SYSTEM, WITH AN ELONGATED AND PARTIALLY EXPOSED LLCC, AS A WIDESPREAD MID-LEVEL CLOUD STRUCTURE WRAPS AROUND THE ASSESSED BEST-TRACK POSITION. THE INITIAL POSITION IS MAINTAINED AS LOW CONFIDENCE AS CIRRUS BLOWOFF AND SOUTHEASTWARD MOVING CONVECTIVE STRUCTURES OBSCURE THE ELONGATED SURFACE CIRCULATION, WHILE MICROWAVE IMAGERY AND SCATTEROMETRY DATA HAS BEEN EXTREMELY LIMITED. THE INITIAL INTENSITY IS ASSESSED AT 40 KNOTS BASED ON PERSISTENCE OF THE OBSERVABLE PARTIALLY EXPOSED LLCC ON EIR AND CIMSS INTENSITY ESTIMATES RANGING BETWEEN 35-41 KNOTS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN EDGE OF A DEEP-LAYER NER TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS NFFN: T2.5 - 35 KTS CIMSS ADT: 43 KTS AT 081730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: LOW 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. FORECAST DISCUSSION: TC 12P IS FORECAST TO TRACK GENERALLY EAST-SOUTHEASTWARD THROUGH THE FORECAST PERIOD, ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYER NER DIRECTLY TO THE NORTH. NEAR TAU 72, THE SYSTEM WILL SLOW ITS MOVEMENT TO THE SOUTHEAST AS WEAK STEERING FLOW BECOMES EVIDENT AND THE SYSTEM BECOMES SOMEWHAT QUASI-STATIONARY BETWEEN TAU 72 AND TAU 120, WHILE CHECKMARKING TO THE NORTHWEST THROUGH ITS DISSIPATION PHASE. ALTHOUGH VERTICAL WIND SHEAR (VWS) REMAINS LESS THAN 20 KNOTS THROUGH TAU 48, ENCROACHING DRY AIR WRAPPING INTO THE CENTER FROM THE WEST WILL LIMIT ENHANCED INTENSIFICATION, KEEPING THE INTENSITY TC 12P RELATIVELY STABLE THROUGH TAU 72 AT 45 KNOTS, AND STEADILY DECREASING TO 30 KNOTS INTO TAU 120 WHILE THE SYSTEM DISSIPATES OVER WATER. MODEL MEMBERS OF THE JTWC OBJECTIVE AIDS REMAIN IN GOOD AGREEMENT THAT TC 12P WILL CONTINUE EAST-SOUTHEASTWARD, WITH A CROSS-TRACK SPREAD OF 70NM BY TAU 48 AND DIVERGE UNIFORMLY BY THE END OF THE FORECAST PERIOD UP TO 120NM. MODEL MEMBERS OF THE JTWC INTENSITY CONSENSUS SHOW A SUSTAINED FORECAST BETWEEN 40-45 KNOTS INTO TAU 96, AND STEADILY DECAY TO 30 KNOTS BY TAU 120. MODEL DISCUSSION: GLOBAL NUMERICAL GUIDANCE IS IN GOOD AGREEMENT THAT TC 12P WILL TRACK GENERALLY TO THE EAST-SOUTHEAST THROUGH TAU 96, WHILE DIVERGING INTO TAU 120 WITH MULTIPLE MODEL SOLUTIONS TRACKING THE SYSTEM SLIGHTLY TO THE NORTH AND SOUTH AS A WEAK STEERING ENVIRONMENT INCREASINGLY DOMINATES THE AREA. THE JTWC FORECAST REMAINS JUST NORTH OF THE CONSENSUS MEAN THROUGH THE DURATION OF THE FORECAST PERIOD. BY TAU 120, ALL OF THE GUIDANCE BEGINS TO SHOW A SLOW TRACK MOVEMENT WITH A WESTWARD COMPONENT. DUE TO THE UNCERTAINTY AND INCREASING TRACK SPREAD NEAR THE END OF THE FORECAST PERIOD, FORECAST CONFIDENCE OF BOTH TRACK AND INTENSITY AFTER TAU 72 ARE LOW. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN