WDPN31 PGTW 131500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (MERBOK) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 25.6N 162.8E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 433 NM NORTH-NORTHWEST OF WAKE ISLAND MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 26 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TWO MAIN DEEP CONVECTIVE REGIONS SPINNING CYCLONICALLY ABOUT THE LLCC IMPARTING A COMMA LIKE SHAPE TO THE SYSTEM. A 130730Z SSMIS 91GHZ MICROWAVE IMAGE SHOWS A NEARLY FORMED EYE LIKE STRUCTURE WITH LOW LEVEL CLOUD LINES VISIBLE TO THE WEST OF THE LLCC AND DEEP CONVECTION VISIBLE TO THE EAST. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EIR AND SSMIS IMAGERY. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON ALL LISTED INTENSITY GUIDANCE INDICATING 55-65 KTS WITH THE EXCEPTION OF KNES WHO SITS AT T4.5 (77KTS) DUE TO THEIR PREMATURE USE OF THE EYE METHOD. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUB-TROPICAL RIDGE (STR) TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS RJTD: T3.5 - 55 KTS KNES: T4.5 - 77 KTS CIMSS SATCON: 59 KTS AT 130731Z CIMSS ADT: 55 KTS AT 131140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD 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: TS 15W IS FORECAST TO CONTINUE TRACKING ON THE WESTERN PERIPHERY OF THE STR TO THE EAST. AS THE SYSTEM ROUNDS THE STR AXIS, A GENERALLY NORTH-NORTHWESTWARD TRACK WILL BECOME NORTH-NORTHEASTWARD. AS THIS TAKES PLACE, 15W IS FORECAST TO CONTINUE INTENSIFYING IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY WARM SEA SURFACE TEMPERATURES (SST) (28-29C), LOW VERTICAL WIND SHEAR (VWS) (10-15KTS) AND IMPROVING OUTFLOW ALOFT. AFTER TAU 36, AFTER REACHING A POTENTIAL PEAK INTENSITY OF 85 KTS, SST VALUES WILL BEGIN TO COOL AND VWS WILL INCREASE AS A MID LATITUDE TROUGH APPROACHES FROM THE WEST. AFTER TAU 48, 15W WILL STEADILY INCREASE ITS INTERACTION WITH THIS TROUGH AND PROGRESS THROUGH EXTRA-TROPICAL TRANSITION (ETT) DRAMATICALLY INCREASING TRACK SPEEDS. BY TAU 72, NOW FULLY DEVOID OF TROPICAL CHARACTERISTICS, 15W WILL COMPLETE ETT NEAR THE ALEUTIAN ISLAND CHAIN. MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT THROUGH THE FORECAST PERIOD WITH A 130NM SPREAD AT TAU 72. FOR THIS REASON THE JTWC FORECAST TRACK IS PLACED WITH HIGH CONFIDENCE. WITH THE EXCEPTION OF COAMPS-TC (GFS AND NVGM VERSION) WHICH SHOW EXTREME HIGH AND LOW INTENSITY FORECASTS RESPECTIVELY, RELIABLE MODEL INTENSITY GUIDANCE IS IN FAIR AGREEMENT. THE BULK OF THE GUIDANCE SHOWS ROBUST INTENSIFICATION THROUGH TAU 36 - TAU 48 AFTER WHICH A SHARP DECLINE AS THE SYSTEM PROGRESSES THOUGH ETT. FOR THESE REASONS THE JTWC FORECAST INTENSITY IS PLACED WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN