WDPS31 PGTW 090300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11P (ELEVEN) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.6S 168.9E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 119 NM SOUTH-SOUTHEAST OF PORT VILA, VANUATU MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD BUT CONSOLIDATING SYSTEM WITH A STREAK OF DRY AIR IMPINGING ON THE EASTERN PORTION OF THE CIRCULATION. A 082030Z GMI 89GHZ IMAGE DEPICTS THE CONVECTION SHEARED TO THE NORTHWEST OF THE LOW LEVEL CIRCULATION. THE INITIAL POSITION IS BASED ON THE LOW LEVEL BANDING IN THE PREVIOUSLY MENTIONED GMI IMAGE AND THE INITIAL INTENSITY OF 35 KTS IS BASED ON THE PGTW DVORAK CURRENT INTENSITY ESTIMATE. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS PHFO: T2.5 - 35 KTS NFFN: T2.5 - 35 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-25 KTS SST: 28-29 CELSIUS OUTFLOW: WEAK EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: LOW INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 11P IS FORECAST TO TURN SOUTHWARD OVER THE NEXT 12 HOURS FOLLOWED BY A SOUTHWESTWARD TRACK BY TAU 24 AS THE SUBTROPICAL RIDGE TO THE SOUTHEAST BEGINS TO REORIENT. THE SYSTEM WILL CONTINUE SOUTHWESTWARD, PASSING OVER THE SOUTHERN TIP OF GRANDE TERRE, NEW CALEDONIA AROUND TAU 36. AFTER TAU 48, IT WILL BEGIN TO ACCELERATE SOUTHWARD DUE TO A PASSING SHORT-WAVE TROUGH AND BECOME SUBTROPICAL BY TAU 72. TC 11P IS CURRENTLY IN A MARGINALLY FAVORABLE ENVIRONMENT DUE TO 15-25 KTS OF VERTICAL WIND SHEAR AND WEAK OUTFLOW ALOFT. THIS WILL LIMIT THE SYSTEM TO MODERATE INTENSIFICATION IN THE EARLY PORTION OF THE FORECAST, REACHING 55 KTS BY TAU 36. THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO IMPROVE AFTERWARDS ALLOWING FOR AN INTENSITY OF 65 KTS AROUND TAU 48. BY TAU 60, TC 11P WILL BEGIN EXPERIENCING COOLING SEA SURFACE TEMPERATURES WHICH WILL LIMIT ANY FURTHER INTENSIFICATION. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT IN REGARDS TO TRACK FORECAST WITH ONLY A 150 NM CROSS-TRACK SPREAD AT TAU 72. THEREFORE, THE JTWC FORECAST TRACK IS PLACED CLOSE TO THE CONSENSUS. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT WITH ALL MODELS INDICATING MODERATE INTENSIFICATION UP TO TAU 60 FOLLOWED BY A WEAKENING TREND BEYOND TAU 72. THE JTWC FORECASTS 65 KTS AT TAU 48 AND TAU 72, BUT GFS INDICATES A PEAK INTENSITY OF 70 KTS COULD HAPPEN AT TAU 60. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN