Tropical Storm SAUDEL Advisory pt., 23.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (SAUDEL) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 19W (SAUDEL), LOCATED APPROXIMATELY 277 NM SOUTH-
SOUTHEAST OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
SHOWS THE SYSTEM CONTINUED TO IMPROVE WITH DEEPENED AND MORE COMPACT
CENTRAL CONVECTION WITH OVERSHOOTING CLOUD TOPS NEAR AN IMMINENT EYE
FEATURE. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED
ON A DEFINED MICROWAVE EYE IN THE 222046Z AND 222254Z SSMIS IMAGES. THE
INITIAL INTENSITY OF 85KTS IS BASED ON AGENCY DVORAK ESTIMATES RANGING
FROM T4.5/77KTS (KNES) AND T5.0/90KTS (PGTW AND RJTD). THE ENVIRONMENT
IS NOW MARGINALLY FAVORABLE AS VERTICAL WIND SHEAR (VWS) HAS INCREASED
TO MODERATE (15-20KTS); HOWEVER, THIS IS OFFSET BY WARM (29C) SEA
SURFACE TEMPERATURES (SST) IN THE SOUTH CHINA SEA, AND ROBUST UPPER-
LEVEL OUTFLOW. THE CYCLONE IS IN A COL CREATED BY A SHORTWAVE TROUGH
DIGGING INTO TAIWAN THAT SPLIT THE STEERING SUBTROPICAL RIDGE (STR)INTO
TWO - ONE TO THE WEST AND ONE TO THE EAST, WHICH IS CURRENTLY THE
DOMINANT STEERING MECHANISM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. THE STR TO THE EAST IS EXPECTED TO RE-BUILD AS THE SHORTWAVE
TROUGH ADVANCES EASTWARD, ALLOWING TY 19W TO TRACK SLOWLY ON A MORE
WESTWARD DIRECTION, PASSING JUST SOUTH OF HAINAN, CHINA, AND MAKING
LANDFALL OVER CENTRAL VIETNAM, JUST NORTH OF HUE NEAR TAU 66. THE
MARGINALLY FAVORABLE CONDITIONS WILL MAINTAIN THE CURRENT INTENSITY UP
TO TAU 12. AFTERWARD, COOLING SSTS CAUSED BY TC-INDUCED UPWELLING,
MODERATE VWS, AND DECREASING OUTFLOW WITH THE RECEDING TROUGH WILL
GRADUALLY WEAKEN THE SYSTEM TO 60KTS BY TAU 48, AND RAPIDLY DOWN TO
30KTS BY TAU 72 WITH LAND INTERACTION AFTER LANDFALL. NUMERICAL MODELS
ARE IN BETTER AGREEMENT WITH UEMN THE SOLE LEFT OUTLIER, LENDING FAIR
CONFIDENCE TO THIS PORTION OF THE JTWC TRACK FORECAST.
   C. AFTER TAU 72, TY SAUDEL WILL TRACK MORE WEST-SOUTHWESTWARD AS THE
STR TO THE WEST BECOMES THE DOMINANT STEERING MECHANISM, CROSSING LAOS
AND INTO THAILAND BY TAU 96 WHERE IT WILL DISSIPATE DUE TO FRICTIONAL
EFFECTS OF THE RUGGED TERRAIN. MODEL GUIDANCE DIVERGES SIGNIFICANTLY
AFTER TAU 72 AS SOME MODELS LOSE THE WEAK VORTEX, LENDING LOW
CONFIDENCE TO THIS PORTION OF THE JTWC TRACK FORECAST.
NNNN
NNNN