WDPS31 PGTW 201500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26P (GINA) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.2S 167.3E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 106 NM SOUTH-SOUTHWEST OF PORT VILA, VANUATU MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING CONVECTION ASSOCIATED WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). OVER THE LAST SEVERAL HOURS, WITH THE APPROACH OF THE DIURNAL CONVECTIVE MAXIMUM, THE CONVECTIVE CELL ASSOCIATED WITH THE LLCC HAS PERSISTED WHILE BEING SHEARED TO THE SOUTHEAST. THE STRUCTURE OF TROPICAL CYCLONE 26P (GINA) REMAINS COMPACT, AND THE 201057Z ASCAT-B SCATTEROMETER PASS INDICATES THAT 35 KNOT WINDS ARE CONFINED ONLY TO THE SOUTHEAST QUADRANT ASSOCIATED WITH THE DEEPEST CONVECTION. THE INITIAL POSITION AND INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE. ALTHOUGH POLEWARD OUTFLOW CONTINUES TO BE GOOD, NORTHWESTERLY VERTICAL WIND SHEAR HAS INCREASED TO 25 TO 30 KNOTS OVER THE SYSTEM. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS PHFO: T2.0 - 30 KTS CIMSS SATCON: 39 KTS AT 201054Z CIMSS ADT: 35 KTS AT 201140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 30+ KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THE STRUCTURE OF TROPICAL CYCLONE 26P (GINA) CONTINUES TO BE SIGNIFICANTLY DISRUPTED BY VERTICAL WIND SHEAR OF 25 TO 30 KNOTS, WHICH IS FORECAST TO INCREASE THROUGH TAU 36. DRY AIR HAS BEGUN TO WRAP AROUND THE CIRCULATION, WHICH IS SUPPRESSING CONVECTION IN ALL BUT THE SOUTHEAST QUADRANT. THE CURRENT INTENSITY OF 35 KNOTS IS SUSTAINED BY PERIODIC CONVECTIVE BURSTS. HOWEVER, GRADUAL WEAKENING SHOULD COMMENCE WITH DISSIPATION EXPECTED IN 24 TO 36 HOURS. GINA IS TRACKING SOUTHWESTWARD AROUND THE SUBTROPICAL RIDGE TO ITS EAST. A TURN TOWARD THE SOUTH AND THEN SOUTHEAST IS EXPECTED BY TAU 36 AS IT ROUNDS THE RIDGE. NUMERICAL MODEL GUIDANCE GENERALLY AGREES WITH THIS SCENARIO. HOWEVER, THERE IS SOME UNCERTAINTY ASSOCIATED WITH THE DEGREE TO WHICH CONVECTIVE BURSTS WILL CONTRIBUTE TO SLIGHT DEVIATIONS IN TRACK AS THE VORTEX EVENTUALLY DECOUPLES. THUS, THE CONFIDENCE IN THE TRACK AND INTENSITY FORECASTS IS ASSESSED AT MEDIUM AND HIGH, RESPECTIVELY. MODEL DISCUSSION: ALTHOUGH NUMERICAL MODEL GUIDANCE INDICATES A 105 NM SPREAD AT TAU 36, ALL MODELS SUGGEST A GRADUAL TURN TOWARD THE SOUTH AND SOUTHEAST OVER THE NEXT 24 HOURS AS GINA ROUNDS THE SUBTROPICAL RIDGE. THE JTWC TRACK AND INTENSITY FORECASTS ARE PLACED NEAR THE MULTI-MODEL CONSENSUS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH// NNNN