Tropical Storm SAUDEL Advisory 10月22日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (SAUDEL) WARNING NR
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 19W (SAUDEL), LOCATED APPROXIMATELY 496 NM
EAST OF DA NANG, VIETNAM, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS
(KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY SHOWS THE CENTRAL CONVECTION CONTINUED TO DEEPEN AND EXPAND,
TOTALLY OBSCURING THE LOW LEVEL CIRCULATION (LLC). RELATIVELY
SHALLOW RAIN BANDS ALSO WRAPPED TIGHTER INTO THE LLC. THE INITIAL
POSITION IS PLACED WITH FAIR CONFIDENCE USING EXTRAPOLATION FROM AN
ELONGATED BUT DEFINED LLC IN THE 211359Z 25KM DIRECT ASCAT PASS. THE
INITIAL INTENSITY OF 60KTS IS AVERAGED FROM AGENCY DVORAK ESTIMATES
OF T3.5-4.0 (55-65KTS) AND REFLECTS THE IMPROVED STATE OF THE
SYSTEM. OVERALL, THE ENVIRONMENT IS FAVORABLE FOR CONTINUED
DEVELOPMENT WITH LOW (10-15KT) VERTICAL WIND SHEAR (VWS), WARM (29-
30C) SEA SURFACE TEMPERATURES (SST) IN THE SOUTH CHINA SEA, AND NEAR-
RADIAL UPPER-LEVEL OUTFLOW. A SHORTWAVE TROUGH CURRENTLY DIGGING
INTO THE TAIWAN STRAIT HAS WEAKENED THE STEERING SUBTROPICAL RIDGE
(STR), PULLING THE CYCLONE POLEWARD INTO THE COL FORMED BETWEEN THE
SPLIT STRS - ONE TO THE WEST AND ONE TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. OVER THE NEXT TWO DAYS, TS 19W WILL TRACK VERY SLOWLY OR
BECOME QUASI-STATIONARY IN THE COL. AFTERWARD, THE NEW STR TO THE
EAST WILL BUILD AND EXTEND WESTWARD, BECOME THE DOMINANT STEERING
MECHANISM, AND SLOWLY DRIVE THE CYCLONE WESTWARD TOWARD CENTRAL
VIETNAM. BY TAU 72, TS 19W WILL HAVE REACHED A POINT APPROXIMATELY
85NM SOUTHEAST OF HAINAN, CHINA. THE FAVORABLE ENVIRONMENT WILL FUEL
INTENSIFICATION TO A PEAK OF 70KTS BY TAU 24; AFTERWARD, COOLING SST
DUE TO UPWELLING IN THE COL AND INCREASING VWS AS THE CYCLONE TRACKS
WESTWARD WILL GRADUALLY WEAKEN THE SYSTEM AND BY TAU 72, WILL BE
DOWN TO 45KTS. NUMERICAL MODELS ARE IN AGREEMENT AS FAR AS RETAINING
THE SYSTEM IN THE COL FOR A PERIOD OF TIME. HOWEVER, THEY OFFER
VARYING SOLUTIONS AS TO WHEN THE CYCLONE WILL EXIT OUT OF THE COL
WITH NVGM TAKING A MORE POLEWARD TRACK AND AFUM/UEMN TAKING A MORE
DELAYED LOOPING MOTION. IN VIEW OF THESE, THERE IS LOW CONFIDENCE IN
THIS PORTION OF THE JTWC TRACK FORECAST.
   C. BEYOND TAU 72, TS SAUDEL WILL TRACK WEST-SOUTHWESTWARD UNDER
THE NEW STR AND MAKE LANDFALL JUST NORTH OF HUE, VIETNAM, PRIOR TO
TAU 96, DRAG ACROSS LAOS, AND ENTER THAILAND BY TAU 120. THE RUGGED
TERRAIN WILL PRIMARILY ERODE THE SYSTEM, AND BY TAU 120, REDUCE IT
TO 25KTS. THERE IS ALSO LOW CONFIDENCE IN THE EXTENDED PORTION OF
THE JTWC FORECAST TRACK BECAUSE IT IS DEPENDENT OF THE NEAR-TO-MID
TERM PORTION OF THE FORECAST TRACK.//
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