MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (BAILU) WARNING NR 04// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 12W (BAILU), LOCATED APPROXIMATELY 674 NM SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED WEST-NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS CONVECTION CONTINUES TO CONSOLIDATE AROUND THE LOW LEVEL CIRCULATION CENTER (LLCC) WITH MOST OF THE DEEP CONVECTION OFFSET TO THE SOUTHWEST. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON EIR IMAGERY WHICH SHOWS BANDING WRAPPING INTO THE LLCC. THE INTENSITY OF 45 KNOTS IS SET ABOVE DVORAK CURRENT INTENSITY ESTIMATES OF T2.0-2.5 (30-42 KNOTS) AND IS SLIGHTLY ABOVE A 212214Z SATCON ESTIMATE OF 43 KNOTS. A PARTIAL 210030Z METOP-B ASCAT PASS SHOWS A SMALL SWATH OF 40-45 KNOT WIND BARBS WITHIN THE SOUTHERN SEMI-CIRCLE. ENVIRONMENTAL ANALYSIS SHOWS TS 12W IS EXPERIENCING FAVORABLE VERTICAL WIND SHEAR (5 TO 15 KNOTS). TS 12W HAS A STRONG EQUATORWARD OUTFLOW CHANNEL AND A TROPICAL UPPER TROPOSPHERIC TROUGH IS BEGINNING TO ENHANCE POLEWARD OUTFLOW TO THE NORTHEAST. SEA SURFACE TEMPERATURES REMAIN FAVORABLE (28-29 DEGREES CELSIUS) FOR DEVELOPMENT. TS 12W IS TRACKING NORTHWESTWARD WHILE UNDER THE INFLUENCE OF A SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE OVERALL FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. IN THE SHORT TERM, TS 12W WILL CONTINUE TO EXPERIENCE FAVORABLE VERTICAL WIND SHEAR AND WILL REMAIN OVER WARM SEA SURFACE TEMPERATURES. THESE CONDITIONS WILL ALLOW FOR A RAPID INCREASE IN INTENSITY, REACHING 80 KNOTS BY TAU 48. HOWEVER, A POOR UPPER LEVEL ENVIRONMENT AROUND TAU 48 WILL HINDER FURTHER INTENSIFICATION. THE STR TO THE NORTHEAST WILL REMAIN IN PLACE THROUGH TAU 72 AND ALLOW TS 12W TO TRACK NORTHWESTWARD. TS 12W WILL MAKE LANDFALL IN TAIWAN AROUND TAU 60. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT, WITH A SPREAD OF 110NM AT TAU 48; HOWEVER, DUE TO THE UNCERTAINTY IN THE INITIAL POSITION THERE IS MODERATE CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK. C. AFTER TAU 72, TS 12W WILL CONTINUE TO TRACK NORTHWESTWARD WHILE UNDER THE INFLUENCE OF THE STR. BY TAU 72, TS 12W WILL EMERGE INTO THE TAIWAN STRAIT AND THEN MAKE LANDFALL IN CENTRAL CHINA. LAND INTERACTION WITH CHINA WILL CAUSE TS 12W TO WEAKEN QUICKLY AFTER LANDFALL AND WILL DISSIPATE BY TAU 120. DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT DURING THIS PORTION OF THE FORECAST DUE TO A BIFURCATION IN MODEL GUIDANCE. THE JTWC TRACK IS IN AGREEMENT WITH A WEST-NORTHWESTERN PATH SOUTH OF THE STR AND IS NOT EXPECTED TO RECURVE, AS SEEN IN THE ECMWF AND UKMET TRACKS. DUE TO THE MODEL SPREAD AND THE HIGH UNCERTAINTY IN THE INITIAL POSITION THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN