MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (GAEMI) WARNING NR 14// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (GAEMI), LOCATED APPROXIMATELY 575 NM EAST OF HUE, VIETNAM, HAS TRACKED WESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS FULLY EXPOSED, WITH DEEP CONVECTION BEING SHEARED TO THE WEST. THE INITIAL INTENSITY IS BASED ON THE EIR ANIMATION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY IS BASED ON CONGRUENT DVORAK ESTIMATES OF 35 KNOTS FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS 08 DEGREES SOUTH OF THE RIDGE AXIS IN AN AREA OF MODERATE (15-20 KNOT) VERTICAL WIND SHEAR (VWS). THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A BUILDING SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 21W IS FORECAST TO CONTINUE TRACKING WESTWARD ACROSS THE SOUTH CHINA SEA TOWARDS VIETNAM UNDER THE STEERING INFLUENCE OF THE STR AND WILL MAKE LANDFALL SOUTH OF HUE BEFORE TAU 48. WITH THE STORM MOTION NOW IN-PHASE WITH THE UPPER LEVEL WIND FLOW, THE VWS WILL BE MITIGATED AND IN TURN ALLOW TS 21W TO INTENSIFY THROUGH TAU 36. HOWEVER, THE INTENSIFICATION WILL BE TEMPERED BY UPPER LEVEL SUBSIDENCE FROM THE STR. AFTER IT MAKES LANDFALL, THE STORM WILL RAPIDLY WEAKEN DUE TO FRICTIONAL EFFECTS AND DISSIPATE BY TAU 72. MODEL GUIDANCE CONTINUES REMAINS AGGRESSIVE ON THE TRACK SPEED. THIS FORECAST, ON THE OTHER HAND, FAVORS SLOWER INITIAL TRACK SPEEDS. DUE TO THE LARGE DIFFERENCES IN MODEL TRACK SPEEDS, THERE IS LOW CONFIDENCE IN THE TRACK FORECAST. // NNNN NNNN