Tropical Storm SON-TINH Advisory Cts, 27.10.

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.//
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