MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 33W (TEMBIN) WARNING NR 21// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 33W (TEMBIN), LOCATED APPROXIMATELY 148 NM SOUTH-SOUTHWEST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED WESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH LITTLE TO NO ASSOCIATED DEEP CONVECTION. WHAT CONVECTION THERE IS, IS SHEARED OVER 150 NM TO THE NORTHWEST OVER SOUTHERN CAMBODIA. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED INFRARED SATELLITE IMAGERY AND IS SUPPORTED BY A 251448Z AMSU-B 89GHZ MICROWAVE IMAGE, WITH SHALLOW BANDING WRAPPING INTO THE LLCC. THE INITIAL INTENSITY IS ASSESSED AT 40 KNOTS, WHICH IS SUPPORTED BY THE DVORAK FINAL-T INTENSITY ESTIMATES OF T2.5 (35 KNOTS) FROM PGTW AND KNES, HEDGED SLIGHTLY HIGHER DUE TO PREVIOUS SCATTEROMETER DATA INDICATING A BROAD AREA OF 40 KNOT WINDS TRAPPED BETWEEN THE LLCC AND THE VIETNAM COAST. ENVIRONMENTAL CONDITIONS REMAIN MARGINAL WITH MODERATE (20-25 KNOTS) VERTICAL WIND SHEAR (VWS), GOOD POLEWARD OUTFLOW AND MARGINAL VALUES OF SST NEAR 26C. WHILE THESE FACTORS ARE GENERALLY SUPPORTIVE OF DEVELOPMENT, AN UPPER-LEVEL TROUGH HAS DEVELOPED OVER THE PAST SIX HOURS JUST TO THE SOUTHEAST TS 33W, WHICH IS INDUCING CONVERGENT FLOW OVER THE SYSTEM AND CONTRIBUTING TO ITS WEAKENING. TS 33W IS TRACKING STEADILY WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE EAST- WEST ORIENTED SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 33W WILL CONTINUE TO TRACK WESTWARD, PASSING NEAR OR JUST OVER THE SOUTHERN TIP OF VIETNAM WITHIN THE NEXT 12 HOURS, THEN TURN TO A MORE WEST-NORTHWESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD. TS 33W IS FORECAST TO CONTINUE TO SLOWLY WEAKEN DUE TO PERSISTENT MODERATE VWS AND CONVERGENT FLOW ALOFT AS IT TRACKS GULF OF THAILAND. BY TAU 36, THE SYSTEM WILL BE A MINIMAL TROPICAL DEPRESSION AND IS FORECAST TO DISSIPATE AS IT CROSSES THE MALAY PENINSULA, FULLY DISSIPATING IN THE EASTERN BAY OF BENGAL BY TAU 48. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH THE FORECAST PERIOD, LENDING HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN NNNN