Tropical Storm SAUDEL Advisory 10月23日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (SAUDEL) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 19W (SAUDEL), LOCATED APPROXIMATELY 287 NM SOUTH-
SOUTHEAST OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY SHOWS THE SYSTEM CONTINUED TO IMPROVE WITH DEEPENED CENTRAL
CONVECTION AND FEEDER BANDS WRAPPING TIGHTLY INTO AN OBSCURED LOW
LEVEL CIRCULATION. SANS ANY RECENT MICROWAVE IMAGERY AND ASCAT
PASSES, THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON
A LOOSE CLUSTER OF AGENCY FIXES AND EXTRAPOLATION FROM CURRENT STORM
MOTION. THE INITIAL INTENSITY OF 75KTS IS BASED ON THE DVORAK
ESTIMATES OF T4.5/77KTS FROM PGTW AND KNES AND CONSISTENT WITH THE
IMPROVED EIR STRUCTURE. THE ENVIRONMENT REMAINS FAVORABLE WITH LOW
(10-15KT) VERTICAL WIND SHEAR (VWS), WARM (29C) SEA SURFACE
TEMPERATURES (SST) IN THE SOUTH CHINA SEA, AND NEAR-RADIAL 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 BY TAU 72. THE
FAVORABLE CONDITIONS WILL FUEL FURTHER INTENSIFICATION TO A PEAK OF
80KTS BY TAU 12. AFTERWARD, COOLING SSTS CAUSED BY TC-INDUCED
UPWELLING AND DECREASING OUTFLOW WITH THE RECEDING TROUGH WILL
GRADUALLY WEAKEN THE SYSTEM TO 60KTS BY TAU 48, AND RAPIDLY TO 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.
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