WDXS31 PGTW 091500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 03S (THREE) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 9.7S 68.4E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 289 NM WEST-SOUTHWEST OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL CYCLONE 03S WITH AN ELONGATED, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AND DEEP CONVECTION SHEARED OFF TO THE WEST. THE WIND FIELD REMAINS HIGHLY ASYMMETRIC WITH THE STRONGEST WINDS CONFINED TO THE SOUTHERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS INDICATES THAT 03S IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG WESTWARD OUTFLOW, MODERATE (15-20 KTS) EASTERLY VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT FROM THE NORTH, AND WARM (27-28 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE LISTED AGENCY DVORAK AND OBJECTIVE INTENSITY EST IMATES RANGING FROM 30-37 KTS. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A SUBTROPICAL RIDGE POSITIONED TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS FMEE: T2.0 - 30 KTS CIMSS ADT: 37 KTS AT 091200Z CIMSS AIDT: 36 KTS AT 091200Z CIMSS D-PRINT: 33 KTS AT 091200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG WESTWARD OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE NORTH ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: 03S IS FORECAST TO TRACK WEST-SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TO THE SOUTH THROUGH TAU 24. NEAR TAU 24, AN INCOMING UPPER-LEVEL TROUGH WILL MOMENTARILY BREAK DOWN THE RIDGE, CAUSING THE STEERING PATTERN TO REORIENT. A SECOND SUBTROPICAL RIDGE IS EXPECTED TO BUILD IN EAST OF MADAGASCAR AROUND TAU 36 AND EXTEND OUT TOWARD THE SYSTEM. 03S WILL THEN TRACK NORTHWESTWARD, ALONG THE NORTHEASTERN PERIPHERY OF THE BUILDING RIDGE THROUGH TAU 72. THE TRAJECTORY WILL THEN BECOME GENERALLY WESTWARD THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. REGARDING INTENSITY, 03S IS FORECAST TO NEARLY MAINTAIN AN INTENSITY OF 35 KTS THROUGH TAU 96. THE INTENSITY WILL BE HINDERED BY PERSISTENT EASTERLY SHEAR AND ASYMMETRICAL WIND FIELD. THE STRONGEST WINDS WILL REMAIN WITHIN THE SOUTHERN SEMI-CIRCLE THROUGHOUT THE FORECAST. A SLIGHT BUMP TO 40 KTS IS FORECAST TO OCCUR AT TAU 36 AS THE VORTEX MOISTENS AND BECOMES MORE VERTICALLY ALIGNED. AFTER THE SYSTEM CROSSES THE 60E LONGITUDE, SEA SURFACE TEMPERATURES ARE EXPECTED TO DROP TO 25-26 C AND DRY AIR ENTRAINMENT WILL INCREASE. THESE TWO FACTORS, ALONG WITH INCREASING EASTERLY SHEAR, WILL CAUSE 03S TO DISSIPATE NEAR TAU 120. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE AGREEMENT THROUGH TAU 48 WITH A 154 NM CROSS-TRACK SPREAD AT THAT TIME. AFTER TAU 48, MODELS BEGIN TO DIVERGE, PARTICULARLY IN THE ALONG-TRACK DIRECTION. THERE IS OVER 300 NM OF ALONG-TRACK SPREAD AT TAU 120. GFS AND NAVGEM ARE THE TWO FASTEST MODELS WHILE THE ECMWF ENSEMBLE MEAN IS THE SLOWEST. THE JTWC TRACK FORECAST IS PLACED IN LINE WITH THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE OVERALL AGREES ON A STEADY INTENSITY OF 30-40 KTS THROUGH TAU 48. AFTERWARD, THE GFS WEAKENS THE SYSTEM MORE QUICKLY THAN THE REMAINDER OF GUIDANCE, SUGGESTING 25 KTS AT TAU 72. ON THE OTHER HAND, HAFS-A AND HWRF MAINTAIN 35 KTS THROUGH TAU 108. THE JTWC INTENSITY FORECAST REMAINS STABLE AT 35 KTS THROUGH TAU 96, ALIGNING MORE WITH THE LATTER MODEL GUIDANCE WITH OVERALL MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN