WDPN31 PGTW 250900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 007// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.3N 143.3E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 191 NM NORTHWEST OF TINIAN MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 19 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM (TS) 12W (KROSA) WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AND ASSOCIATED FLARING CONVECTION THROUGHOUT THE SOUTHERN AND WESTERN QUADRANTS. ALTHOUGH THE LLCC HAS REMAINED PARTIALLY OBSERVABLE THROUGH ANIMATED MSI, THE CENTER HAS BECOME INCREASINGLY OBSCURED WITH PERSISTENT BUT SHORT-LIVED CONVECTION IN CLOSE PROXIMITY TO THE CENTRAL VORTEX OVER THE LAST FEW HOURS. WITH REGARD TO THE ENVIRONMENTAL ANALYSIS, HIGH VERTICAL WIND SHEAR (VWS) BETWEEN 30-35 KTS HAS CONTINUED TO OFFSET FAVORABLE WARM SEA SURFACE TEMPERATURES (29-30 C) AND MODERATE EQUATORWARD OUTFLOW ALOFT. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED PARTIALLY EXPOSED LLCC OBSERVED ON ANIMATED MSI. THE INITIAL INTENSITY IS ALSO ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EARLIER 242320Z METOP B ASCAT IMAGE AND SUBJECTIVE AGENCY DVORAK FIXES LISTED BELOW. LASTLY, RECENT OBJECTIVE CIMSS ESTIMATES RANGE BETWEEN 31 KTS AND 41 KTS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: BUILDING SUBTROPICAL RIDGE TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T2.0 - 30 KTS KNES: T1.5 - 25 KTS CIMSS SATCON: 41 KTS AT 250600Z CIMSS ADT: 33 KTS AT 250710Z CIMSS AIDT: 34 KTS AT 250710Z CIMSS D-MINT: 29 KTS AT 250344Z CIMSS D-PRINT: 31 KTS AT 250710Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 30-35 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 12W IS FORECASTED TO TRACK GENERALLY TO THE NORTH-NORTHEAST THROUGHOUT THE ENTIRETY OF THE 120 HOURS FORECAST. AS THE SUBTROPICAL STEERING RIDGE CONTINUES TO BUILD JUST TO THE EAST, THE SYSTEM WILL MOVE ANTICYCLONICALLY AROUND THE WESTERN PERIPHERY OF THE DEEP-LAYER RIDGE INTO TAU 120. BETWEEN TAU 72 AND TAU 96, AN ADDITIONAL LOW-LEVEL BELT OF ENHANCED SOUTHWESTERLY WINDS EXTENDING FROM THE SOUTHWEST TO THE NORTHEAST JUST SOUTH OF TS KROSAS FORECASTED POSITION WILL INTERACT WITH THE CYCLONE, AIDING IN THE EXPECTED NORTHEAST TRACK BETWEEN TAU 96 AND TAU 120. WITH REGARDS TO INTENSITY, 12W IS FORECASTED TO CONTINUE STEADILY INTENSIFYING TO 65 KTS THROUGHOUT THE NEXT 48 HOURS WITH ASSISTANCE FROM AN UPPER-LEVEL SHORTWAVE TROUGH, PROVIDING AN ORGANIZED MECHANISM FOR OUTFLOW ALOFT. STARTING AT TAU 72, TS 12W IS EXPECTED TO BEGIN SLOWLY WEAKENING TO 60 KTS INTO THE END OF THE 120 FORECAST PERIOD AS DRY AIR ENTRAINS INTO THE CENTRAL VORTEX DUE TO INFLUENCES FROM AN UPPER-LEVEL CYCLONE. AT THE SAME TIME, VWS IS FORECASTED TO SHARPLY DECREASE TO LESS THAN 20 KTS, ALLOWING THE SYSTEM TO SUSTAIN 60 KTS FROM TAU 72 TO TAU 120. MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION (NWP) TRACK GUIDANCE IS IN FAIR AGREEMENT DURING THE INITIAL 72 HOURS OF THE FORECAST, WITH A 217 NM CROSS TRACK SPREAD (NAVGEM BEING THE ONLY OUTLIER). AFTER TAU 72, NWP TRACK SOLUTIONS DIVERGE CONSIDERABLY DUE TO COMPETING STEERING MECHANISMS UNTIL TAU 120. MANY OF THE VARIATIONS IN TRACK SOLUTIONS ARE DUE TO THE EXPECTED SPEED OF APPROACH, WITH GALWEM, UKMET ENSEMBLE, AND UKMET DETERMINISTIC INCREASING SPEED EASTWARD AFTER TAU 96, WHILE GFS, ECMWF, AND NAVGEM SLOW THE TRACK SPEED BEFORE THE EXPECTED EASTWARD TRACK. THE JTWC TRACK FORECAST IS ALIGNED CLOSELY WITH THE JTWC MULTI-MODEL CONSENSUS THROUGH TAU 72 AND FOLLOWS THE SLOWER TRACK SOLUTIONS THEREAFTER. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT INTENSIFICATION TO 65 KTS IS EXPECTED INTO TAU 48, WITH A SLOW WEAKENING STAGE THEREAFTER. THE ONLY INTENSITY OUTLIER IS COAMPS-TC, WITH A MAXIMUM EXPECTED INTENSITY TO 85 KTS BETWEEN TAU 48 AND TAU 60. THE JTWC INTENSITY FORECAST REMAINS ALIGNED WITH THE INTENSITY CONSENSUS, LENDING MEDIUM CONFIDENCE TO THE FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN