WDPN31 PGTW 240900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 12W (KROSA) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 15.2N 143.5E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 119 NM NORTHWEST OF ROTA MOVEMENT PAST 6 HOURS: NORTHWARD AT 13 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION (TD) 12W (KROSA) WITH A PARTIALLY EXPOSED DISORGANIZED AND FRAGMENTED LOW-LEVEL CIRCULATION CENTER (LLCC). FLARING CONVECTION HAS CONTINUED THROUGHOUT THE SOUTHERN SEMICIRCLE, HOWEVER, ELEVATED WIND SHEAR ABOVE 30 KTS HAS RESTRICTED ANY STRUCTURED CURVED BANDS FROM WRAPPING IN CLOSE PROXIMITY TO THE ASSESSED CENTER. ANIMATED WATER VAPOR IMAGERY CONFIRMS A HECTIC AND DISORGANIZED CENTRAL STRUCTURE, AS ANY SUPPORTIVE OUTFLOW MECHANISM NEAR THE LLLCC HAS REMAINED LIMITED WITH NO DEFINITIVE POLEWARD OR EQUATORWARD CHANNEL ALOFT. ENVIRONMENTAL ANALYSIS HAS CONTINUED AS MARGINALLY FAVORABLE, WITH MODERATE EQUATORWARD OUTFLOW, WARM SEA SURFACE TEMPERATURES (29-30 C), AND HIGH VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON EXTRAPOLATION FROM AN EARLIER 240314Z 89 GHZ MICROWAVE IMAGE AND ANIMATED MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EARLIER 240029Z ASCAT IMAGE AND THE PERSISTENT FRAGMENTED STRUCTURE OF 12W. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WEAK SUBTROPICAL RIDGING (STR) TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.0 - 25 KTS KNES: T1.5 - 25 KTS CIMSS SATCON: 34 KTS AT 240630Z CIMSS ADT: 33 KTS AT 240700Z CIMSS AIDT: 33 KTS AT 240700Z CIMSS D-MINT: 26 KTS AT 240351Z CIMSS D-PRINT: 26 KTS AT 240700Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 30+ KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: LOW INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TD 12W IS FORECASTED TO CONTINUE TRACKING GENERALLY NORTHWARD THROUGHOUT TAU 120. AS THE SYSTEM TRACKS NORTHWARD, SUBTROPICAL RIDGING TO THE EAST IS EXPECTED TO BUILD WESTWARD AND SOUTHWESTWARD, INITIATING A SLIGHT NORTH-NORTHEASTWARD TRACK BETWEEN TAU 24 AND TAU 48 ALONG THE WESTERN PERIPHERY OF THE AFOREMENTIONED RIDGE. WHILE THE STR BUILDS TO THE EAST, SYSTEM MOVEMENT IS FORECASTED TO QUICKEN BETWEEN TAU 72 AND TAU 96. NEAR THE END OF THE FORECAST PERIOD, AN ADDITIONAL RIDGE IS EXPECTED TO BUILD TO THE NORTH NEAR THE SEA OF JAPAN, SLOWING NORTHWARD MOVEMENT INTO THE END OF THE FORECAST PERIOD. WITH REGARD TO INTENSITY, TD 12W IS FORECAST TO STEADILY INTENSIFY OVER THE NEXT 72 HOURS. ALTHOUGH VWS IS EXPECTED TO REMAIN RELATIVELY HIGH, ADDITIONAL UPPER-LEVEL OUTFLOW SUPPORT FROM A SHORTWAVE TROUGH WILL AID THE SYSTEM DURING ITS CONTINUED DEVELOPMENT. WHILE THE SYSTEM TRACKS NORTHWARD WITH AN EXPECTED INTENSIFICATION TO 60 KTS BY TAU 72, STEADY HIGH VWS AND DRY AIR ENTRAINMENT WILL LIMIT INTENSIFICATION BETWEEN TAU 72 AND TAU 120, INITIATING THE WEAKENING STAGE. NEAR THE END OF THE FORECAST PERIOD, AN UPPER-LEVEL LOW WILL MOVE SOUTH OF HONSHU, FURTHER WEAKENING TD 12W INTO TAU 120 WITH ADDED DRY AIR. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72, WITH A GENERALLY NORTHWARD TRACK WHILE GFS AND THE GFS ENSEMBLE MEAN BEING THE MOST SIGNIFICANT OUTLIERS SHOWING QUICKENED NORTHWARD MOVEMENT OF TD 12W THROUGHOUT THE 120 HOUR FORECAST. THE JTWC TRACK REMAINS IN CLOSE PROXIMITY TO THE MULTI-MODEL SOLUTION UP TO TAU 96, THEN CLOSER ECMWF AND THE ECMWF ENSEMBLE TRACKERS NEAR THE END OF THE FORECAST PERIOD. THE JTWC TRACK FORECAST CONFIDENCE REMAINS MODERATE UP TO TAU 120 DUE TO THE OVERALL AGREEMENT THROUGHOUT THE MAJORITY OF SOLUTIONS, SANS GFS AND THE GFS ENSEMBLE MEAN, ON TRACK DIRECTION AND TRACK SPEED. WITH REGARD TO INTENSITY GUIDANCE, THERE IS GOOD AGREEMENT THAT AN EXPECTED INTENSIFICATION PHASE WILL BE OBSERVED UP TO TAU 72, WITH A SLIGHT WEAKENING STAGE THEREAFTER. ALTHOUGH COAMPS-TC INDICATES INTENSIFICATION UP TO 70 KTS BY TAU 72, THE JTWC INTENSITY FORECAST REMAINS JUST ABOVE THE INTENSITY CONSENSUS UP TO TAU 72, AND SLIGHT WEAKENING INTO TAU 120 DUE TO THE EXPECTED UNFAVORABLE ENVIRONMENT. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW // NNNN