WDPS31 PGTW 082100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05P (FIVE) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.3S 174.1E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 245 NM WEST OF SUVA, FIJI MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 10 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS PERSISTENT DEEP CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION (LLC). HOWEVER, A 081840Z GMI 37GHZ MICROWAVE IMAGE INDICATES DEEP CONVECTIVE BANDING WRAPPING FROM THE NORTHERN SEMICIRCLE INTO THE SOUTHEAST QUADRANT OF A DEFINED CENTER, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW, KNES AND PHFO DVORAK ESTIMATES. TC 05P IS LOCATED UNDER THE NORTHERN PERIPHERY OF AN UPPER-LEVEL TROUGH WITH MODERATE VERTICAL WIND SHEAR (20 KNOTS) AND POSSIBLE DRY AIR ENTRAINMENT, WHICH ARE HINDERING THE DEVELOPMENT OF CORE CONVECTION. EXTENSIVE DEEP CONVECTIVE BANDING PERSISTS ALONG THE NORTHERN AND EASTERN PERIPHERIES OF THE SYSTEM DUE TO VIGOROUS POLEWARD AND EQUATORWARD VENTING, HOWEVER, THIS BANDING IS NOT WRAPPING INTO THE LLC AND REMAINS DISASSOCIATED FROM THE CORE CONVECTION. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: COMPETING STEERING INFLUENCE BETWEEN THE NEAR-EQUATORIAL RIDGE (NER) TO THE NORTHEAST AND THE SUBTROPICAL RIDGE (STR) TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS KNES: T2.0 - 30 KTS PHFO: T2.0 - 30 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 20-25 KTS SST: 22-23 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: POSSIBLE DRY AIR ENTRAINMENT, ESPECIALLY OVER THE WESTERN SEMICIRCLE. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 05P IS FORECAST TO TRACK SLOWLY EAST-SOUTHEASTWARD THROUGH TAU 12 WITHIN THE COMPETING STEERING PATTERN BETWEEN THE NER AND STR. AFTER TAU 12, THE STR SHOULD BUILD TO THE SOUTH AND BECOME THE DOMINANT STEERING INFLUENCE THROUGH TAU 60 WITH A GENERALLY WESTWARD TO WEST-SOUTHWESTWARD TRACK. AFTER TAU 60, AN APPROACHING MAJOR SHORTWAVE TROUGH IS EXPECTED TO WEAKEN THE STR, WHICH WILL LEAD TO A FASTER SOUTHEASTWARD TRACK TOWARD THE BREAK IN THE STR ALONG THE WESTERN AND SOUTHWESTERN PERIPHERY OF THE WEAK STEERING RIDGE POSITIONED TO THE EAST. THE SYSTEM IS EXPECTED TO REMAIN WITHIN A COMPLEX UPPER-LEVEL ENVIRONMENT UNDER A BROAD UPPER-LEVEL TROUGH, HOWEVER, SLIGHT INTENSIFICATION IS ANTICIPATED DUE TO ROBUST POLEWARD OUTFLOW WITH A PEAK INTENSITY OF 50 KNOTS EXPECTED AT TAU 36. AFTER TAU 36, TC 05P WILL GRADUALLY WEAKEN AS IT BECOMES FURTHER EMBEDDED WITHIN THE UPPER-LEVEL TROUGH. AFTER TAU 96, TC 05P IS FORECASTED TO GRADUALLY TRANSITION INTO A SUBTROPICAL CYCLONE. MODEL DISCUSSION: THE NUMERICAL MODELS AND ENSEMBLE GUIDANCE (EPS AND GEFS) SUPPORT THE JTWC FORECAST TRACK WITH FAIR CONFIDENCE WITH SOME UNCERTAINTY IN THE EXACT TRACK DUE TO THE COMPLEX, RAPIDLY-EVOLVING SYNOPTIC PATTERN. THUS, OVERALL CONFIDENCE IN THE JTWC TRACK IS MEDIUM. THERE IS ALSO UNCERTAINTY IN THE JTWC INTENSITY FORECAST DUE TO THE PRESENCE OF THE UPPER-LEVEL TROUGH OVER THE SYSTEM AND THE POTENTIAL FOR DRY AIR ENTRAINMENT, WHICH IS EXPECTED TO LIMIT DEVELOPMENT. THE BULK OF THE RELIABLE INTENSITY GUIDANCE SUPPORTS THE JTWC FORECAST WITH HWRF PEAKING SLIGHTLY HIGHER TO 55 KNOTS. AFTER TAU 72, THE JTWC INTENSITY FORECAST IS LOWER THAN THE INTENSITY GUIDANCE DUE TO INCREASING VERTICAL WIND SHEAR AND COOLER SST VALUES (26-27C). FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN