MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 08W (WIPHA) WARNING NR 07// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 08W (WIPHA), LOCATED APPROXIMATELY 287 NM EAST OF HANOI, VIETNAM, HAS TRACKED NORTH-NORTHWESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH FRAGMENTED DEEP CONVECTIVE BANDING. A 010530Z AMSR2 89GHZ IMAGE DEPICTS SHALLOW BANDING WRAPPING INTO A WELL-DEFINED LLCC, WHICH SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE. A 010245Z ASCAT IMAGE REVEALS A DEFINED CENTER WITH 30 TO 35 KNOT WINDS OVER THE SOUTH AND EAST QUADRANTS, WHICH SUPPORTS THE INITIAL INTENSITY ASSESSMENT OF 35 KNOTS. THE ASCAT AMBIGUITY ANALYSIS, AMSR2 IMAGE, MSI AND A 010716Z GPM 89GHZ IMAGE ALL PROVIDE EVIDENCE OF AN ABRUPT NORTH-NORTHWESTWARD TURN OVER THE PAST 5-6 HOURS, WHICH HAS ALLOWED THE SYSTEM TO REMAIN OVER FAVORABLE SST (28-29C) WITH AN IMPROVED CONVECTIVE SIGNATURE. HOWEVER, THE SYSTEM IS STILL EXPECTED TO TURN GRADUALLY WESTWARD OVER THE NEXT 12 TO 24 HOURS. UPPER-LEVEL ANALYSIS INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT WITH LOW TO MODERATE VERTICAL WIND SHEAR OFFSET BY GOOD POLEWARD AND EQUATORWARD OUTFLOW. TS 08W IS POSITIONED WEST AND SOUTH OF A LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 08W HAS TRACKED NORTH-NORTHWESTWARD IN THE SHORT-TERM DUE TO AN EXTENSION OF THE STR TO THE EAST, HOWEVER, THE SYSTEM WILL GRADUALLY TURN WESTWARD AS IT TRACKS UNDER THE DOMINANT STEERING INFLUENCE OF THE STR ENTRENCHED TO THE NORTH. THERE IS SOME UNCERTAINTY IN THE TIMING OF THIS INEVITABLE WESTWARD TURN, WHICH INTRODUCES SOME UNCERTAINTY IN THE INTENSITY FORECAST AND EXACT TRACK OVER THE GULF OF TONKIN. THE CURRENT JTWC FORECAST TRACK SKIRTS THE SOUTHERN COAST OF CHINA WITH LANDFALL ALONG THE NORTHEAST COAST OF VIETNAM NEAR TAU 42 AND DISSIPATION BY TAU 48 NEAR HANOI. DYNAMIC MODEL GUIDANCE REFLECTS THIS UNCERTAINTY WITH SOME SOLUTIONS FURTHER NORTH OVER THE COAST, WHICH COULD LEAD TO GREATER WEAKENING. DUE TO THIS UNCERTAINTY, THERE IS MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN