WDXS31 PGTW 092100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 25S (KARIM) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.1S 91.1E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 355 NM WEST-SOUTHWEST OF THE COCOS ISLANDS, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 22 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A UNIFORM CENTRAL DENSE OVERCAST (CDO) OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC), WHICH IS POSITIONED UNDER THE NORTHEASTERN EDGE OF THE CDO. A 091837Z ATMS 88 GHZ MICROWAVE IMAGE DIPICTS THE BULK OF THE DEEP CONVECTION IS IN THE EASTERN SEMICIRCLE WITH A PROMINANT CONVECTIVE BANDING FEATURE TO THE SOUTH. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE OBSCURING CDO AND ATMS MICROWAVE IMAGERY. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON AGENCY DVORAK INTENSITY ESTIMATES. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWEST PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS APRF: T3.5 - 55 KTS CIMSS SATCON: 75 KTS AT 091309Z CIMSS ADT: 59 KTS AT 091740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE WESTWARD OTHER FACTORS: DRY AIR ENTRAINMENT IN THE UPPER-LEVELS ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: HIGH INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 25S IS FORECAST TO TRACK SOUTHWARD TO SOUTH-SOUTHEASTWARD ALONG THE WESTERN PERIPHERY OF THE NEAR EQUATORIAL RIDGE (NER) THROUGH TAU 24. DUE TO THE MARGINALLY FAVORABLE ENVIRONMENTAL CONDITIONS THE INTENSITY IS FORECAST TO REMAIN CONSISTANT THROUGH TAU 12. AFTER TAU 12, THE SYSTEM WILL TRACK WITHIN THE STEERING FLOW BETWEEN A BROAD UPPER-LEVEL TROUGH AND A SUBTROPICAL RIDGE POSITIONED TO THE EAST. ENVIRONMENTAL CONDITIONS SHOULD DEGRADE QUICKLY WITH INCREASING VERTICAL WIND SHEAR OF 30-40 KNOTS AND INCREASING CONVERGENCE ALOFT ASSOCIATED WITH THE AFOREMENTIONED UPPER-LEVEL TROUGH. THEREFORE, TC 25S WILL WEAKEN STEADILY. NEAR TAU 36, A STRONG LOW-LEVEL HIGH WILL BUILD TO THE SOUTH EFFECTIVELY HALTING POLEWARD TRACK MOTION AND COMMENCING AN ABRUPT EQUATORWARD TRACK MOTION WITHIN THE LOW-LEVEL SOUTHEASTERLY FLOW. INTERACTION WITH A WEAK BAROCLINIC ZONE, COOLER SST (25-26C) AND SIGNIFICANT ENTRAINMENT OF DRY AIR WILL LEAD TO RAPID DISSIPATION AS THE REMNANTS ACCELERATE NORTHWESTWARD. MODEL DISCUSSION: RELIABLE MODEL GUIDANCE SUPPORTS THE JTWC TRACK PHILOSOPHY WITH OVERALL MEDIUM CONFIDENCE DUE TO DIFFERENCES IN THE TIMING AND EXACT TRACK DURING THE STALL AND SHARP EQUATORWARD TRACK TURN. AFUM AND UEMN UNREALISTICALLY DRIVE THE SYSTEM EASTWARD THROUGH THE FORECAST PERIOD AGAINST THE ENVIRONMENTAL FLOW. THE JTWC INTENSITY FORECAST IS INITIALLY PLACED SLIGHTLY ABOVE THE MODEL GUIDANCE DUE TO THE LINGERING CHANCE OF MINOR INTENSIFICATION THROUGH TAU 12. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN