WDPS31 PGTW 010300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04P (SETH) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 22.2S 157.4E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 403 NM NORTHEAST OF BRISBANE, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS THE FEEDER BANDS HAVE BEGUN TO UNRAVEL AND BREAK UP AS THE SYSTEM CONTINUED TO ELONGATE DUE TO STRONG NORTHWESTERLY VERTICAL WIND SHEAR WHILE MAINTAINING A FLARING DEEP CENTRAL CONVECTION. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE ON THE EXTRAPOLATED INTERSECTION OF THE FEEDER BANDS AND STACKED UNDER THE WARMEST CENTRAL PIXELS IN THE 010000Z IRBD IMAGE. THE INITIAL INTENSITY OF 45KTS IS BASED ON THE PGTW AND ABRF DVORAK ESTIMATES OF T3.0 AND REFLECTS THE DEGRADATION. ANALYSIS INDICATES THE ENVIRONMENT HAS BECOME UNFAVORABLE WITH WARM SSTS AND STRONG POLEWARD OUTFLOW OFFSET BY MODERATE TO STRONG VERTICAL WIND SHEAR AND MID-LEVEL DRY AIR INTRUSION. THE CYCLONE IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE NEAR-EQUATORIAL RIDGE (NER) TO THE NORTHEAST. INITIAL WIND RADII BASIS: SCATTEROMETER DATA SURFACE OBSERVATIONS. CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A NEAR-EQUATORIAL RIDGE (NER) TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS ABRF: T3.0 - 45 KTS CIMSS SATCON: 55 KTS AT 312019Z CIMSS ADT: 51 KTS AT 312040Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 20-25 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: MID-LEVEL DRY AIR INTRUSION FROM THE WEST. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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 SETH WILL CONTINUE ON ITS CURRENT TRACK UNDER THE NER. AFTER TAU 12, A SUBTROPICAL RIDGE TO THE SOUTHEAST WILL ASSUME STEERING AND DRIVE THE SYSTEM MORE SOUTHWARD. THE INCREASINGLY UNFAVORABLE ENVIRONMENT WILL GRADUALLY WEAKEN THE SYSTEM DOWN TO 35KTS BY TAU 36. ALSO, BY TAU 12, THE CYCLONE WILL BEGIN TO TRANSITION TO A SUBTROPICAL SYSTEM AND BY TAU 36, WILL BECOME FULLY SUBTROPICAL WITH AN EXPANSIVE WIND FIELD. MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT, LENDING MEDIUM CONFIDENCE TO THE JTWC TACK AND INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM.// NNNN