WDPS31 PGTW 200900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26P (GINA) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.6S 167.7E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 64 NM SOUTH-SOUTHWEST OF PORT VILA, VANUATU MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS FLARING CONVECTION ASSOCIATED WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). THE LLCC HAS ALTERNATED BETWEEN FULLY EXPOSED AND PARTIALLY OBSCURED BY THE CIRRUS SHIELD OF THE FLARING CONVECTION THAT CONTINUES TO BE SHEARED TO THE SOUTHEAST. THE STRUCTURE OF TROPICAL CYCLONE 26P (GINA) REMAINS COMPACT, AND THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE. THE INITIAL INTENSITY REMAINS 35 KNOTS BASED ON THE STEADY STATE STRUCTURE OF THE SYSTEM SINCE THE 192227Z ASCAT-B SCATTEROMETER PASS. ALTHOUGH POLEWARD OUTFLOW CONTINUES TO BE GOOD, NORTHWESTERLY VERTICAL WIND SHEAR HAS INCREASED TO 20 TO 25 KNOTS OVER THE SYSTEM. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS KNES: T2.0 - 30 KTS NFFN: T3.0 - 45 KTS CIMSS SATCON: 45 KTS AT 200218Z CIMSS ADT: 34 KTS AT 200540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 20-25 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) IS BEING SIGNIFICANTLY DISRUPTED BY MODERATE VERTICAL WIND SHEAR OF 20 TO 25 KNOTS, WHICH IS FORECAST TO INCREASE THROUGH TAU 48. 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 FORECAST TO CONTINUE, SUSTAINED BY PERIODIC CONVECTIVE BURSTS. HOWEVER, GRADUAL WEAKENING SHOULD COMMENCE WITH DISSIPATION EXPECTED BY TAU 36 TO 48. GINA IS TRACKING SOUTHWESTWARD AROUND THE SUBTROPICAL RIDGE TO ITS EAST. A TURN TOWARD THE SOUTH AND THEN SOUTHEAST IS EXPECTED BY TAU 48 AS IT ROUNDS THE RIDGE. NUMERICAL MODEL GUIDANCE GENERALLY AGREES WITH THIS SCENARIO. HOWEVER, THERE IS SOME UNCERTAINTY ASSOCIATED WITH THE TIMING OF VORTEX DECOUPLING AND THE DEGREE TO WHICH CONVECTIVE BURSTS WILL CONTRIBUTE TO SLIGHT DEVIATIONS IN TRACK. THUS, THE CONFIDENCE IN BOTH THE TRACK AND INTENSITY FORECASTS IS ASSESSED AT MEDIUM. MODEL DISCUSSION: THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS. THE JTWC INTENSITY FORECAST IS SLIGHTLY BELOW THE MULTI-MODEL CONSENSUS DUE TO THE EXPECTATION THAT ANY INTENSIFICATION OF 26P IS UNLIKELY IN THE CURRENTLY UNFAVORABLE ENVIRONMENT. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN