WDPN31 PGTW 212100
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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