MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (SON-TINH) WARNING NR 13// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 24W (SON-TINH), LOCATED APPROXIMATELY 270 NM EAST OF HUE, VIETNAM, HAS TRACKED WEST-NORTHWESTWARD AT 13 KTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED IMAGERY DEPICTS TIGHTLY-CURVED CONVECTIVE BANDING WRAPPING AROUND A LOW LEVEL CIRCULATION CENTER (LLCC). A 261804Z AMSU IMAGE ALSO DEPICTS THE CONVECTIVE BANDING, WITH THE DEEPEST CONVECTION FOUND IN THE SOUTHEASTERN QUADRANT. THE INITIAL POSITION IS BASED ON THE PGTW FIX AND IS SUPPORTED BY THE AFOREMENTIONED AMSU IMAGE. THE INITIAL INTENSITY IS BASED ON DVORAK ESTIMATES OF 65 KTS FROM PGTW AND KNES. UPPER-LEVEL ANALYSIS CONTINUES TO DEPICT A FAVORABLE ENVIRONMENT WITH GOOD RADIAL OUTFLOW AND WEAK (05-10 KTS) VERTICAL WIND SHEAR (VWS). THE LATEST UPPER LEVEL SOUNDING FROM XISHA DAO SHOWS THAT 24W IS ENTRAINING MORE MOISTURE INTO THE REGION. SEA SURFACE TEMPERATURES OF 27-28 DEGREES CELSIUS ARE FAVORABLE FOR DEVELOPMENT. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TY 24W IS FORECAST TO CONTINUE TRACKING WEST-NORTHWESTWARD THROUGH THE FORECAST PERIOD UNDER THE STEERING INFLUENCE OF THE DEEP SUB-TROPICAL RIDGE POSITIONED TO THE NORTH. THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK BASED ON THE SOLID STEERING RIDGE AND GOOD AGREEMENT IN DYNAMIC MODEL GUIDANCE THROUGH TAU 36 WITH A 125 NM SPREAD. MODEL GUIDANCE HAS BEEN COMING INTO BETTER AGREEMENT ON THE LANDFALL SCENARIO, CALLING FOR TY 24W TO DECELERATE AFTER MAKING LANDFALL OVER VIETNAM. GFDN IS NOW THE SOLE OUTLIER, TRACKING THE SYSTEM WESTWARD INTO LAOS. TY 24W IS FORECAST TO INTENSIFY TO A PEAK OF 85 KTS BY TAU 24. ALTHOUGH TY 24W IS EXPECTED TO TRACK OVER MARGINAL OCEAN HEAT CONTENT, STRONG RADIAL OUTFLOW AND LOW VWS SHOULD OFFSET ANY MITIGATING FACTORS. BY TAU 36, TY 24W SHOULD BEGIN TO WEAKEN AS IT INTERACTS WITH THE COAST OF VIETNAM, WITH RAPID WEAKENING COMMENCING AFTER LANDFALL DUE TO FRICTIONAL EFFECTS. C. IN THE EXTENDED TAUS, TY 24W IS FORECAST TO SLOW SIGNIFICANTLY OVER NORTHERN VIETNAM AND DISSIPATE BY TAU 96. MODEL GUIDANCE INDICATES INCREASING UPPER-LEVEL WESTERLY FLOW OVER NORTHERN VIETNAM, WHICH IS EXPECTED TO HALT THE WESTWARD PROGRESSION AND TURN THE SYSTEM EASTWARD. IN GENERAL, MODEL GUIDANCE INDICATES RAPID WEAKENING WITH THE REMNANTS TRACKING OVER THE GULF OF TONKIN. DUE TO UNCERTAINTIES ASSOCIATED WITH THE TIMING AND STRENGTH OF INTERACTION BETWEEN TY 24W AND THE SUB-TROPICAL WESTERLIES, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE FORECAST.// NNNN NNNN