WDPN31 PGTW 210300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (SAUDEL) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS. 
   TROPICAL STORM (TS) 19W (SAUDEL), LOCATED APPROXIMATELY 196 NM 
NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 16 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY AND A 20/2321Z SSMIS 91GHZ IMAGE INDICATE A CONSOLIDATING 
SYSTEM WITH CONVECTIVE BANDING WRAPPING INTO A RAGGED LOW LEVEL 
CIRCULATION CENTER. THE INITIAL INTENSITY IS ASSESSED AT 45 KNOTS 
BASED ON A PGTW DVORAK INTENSITY ESTIMATE OF 3.0/3.5 (45/55 KNOTS). 
NEAR-RADIAL UPPER LEVEL OUTFLOW, LOW (10-15 KT) VERTICAL WIND SHEAR 
(VWS), AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES CONTRIBUTE 
TO AN OVERALL FAVORABLE ENVIRONMENT FOR CONTINUED DEVELOPMENT. TS 
19W IS TRACKING ALONG THE SOUTHEASTERN PERIPHERY OF A WEAKENING 
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHWEST. 500MB ANALYSES 
OVER THE PAST TWO DAYS SHOW A RECEDING WESTERN STR (HIGH CENTER JUST 
NORTHEAST OF HAINAN ISLAND) WITH A BREAK LOCATED EAST OF TAIWAN. 
ADDITIONALLY, THE MAJOR SHORTWAVE TROUGH PREDICTED BY THE MODELS TO 
DIG INTO SOUTHEAST CHINA IS IN FACT DIGGING INTO SOUTHEAST CHINA; 
THE SHORTWAVE TROUGH IS LOCATED ABOUT 110E WITH COLD AIR ADVECTION 
INTO THE NORTHERN PERIPHERY OF THE STR, WHICH WILL SERVE TO FURTHER 
WEAKEN THE STEERING STR OVER THE NEXT DAY.     
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 19W WILL CONTINUE TO TRACK GENERALLY WESTWARD UNDER THE 
STEERING INFLUENCE OF THE STR THROUGH TAU 12. HOWEVER, THE SYSTEM IS 
EXPECTED TO SLOW AND GRADUALLY TURN WEST-NORTHWESTWARD TO 
NORTHWESTWARD AS THE STR WEAKENS AND A COL REGION FORMS NORTH OF THE 
SYSTEM. THERE IS SIGNIFICANT UNCERTAINTY IN THIS STAGE OF THE 
FORECAST WITH A QUICKLY EVOLVING SYNOPTIC PATTERN AND DYNAMIC 
SHORTWAVE TROUGH APPROACHING. THE BULK OF THE NUMERICAL GUIDANCE IS 
IN FAIR AGREEMENT WITH SOME DIFFERENCES IN THE TIMING / DURATION OF 
THE SHORT-TERM POLEWARD TURN. AFTER TAU 48, THE SHORTWAVE TROUGH IS 
FORECAST TO PROPAGATE EASTWARD AND THE STR TO REBUILD, WHICH WILL  
ALLOW THE SYSTEM TO RESUME ITS WESTWARD TRACK. TS 19W SHOULD 
STEADILY INTENSIFY TO A PEAK OF 60 KTS BY TAU 48 UNDER CONTINUED 
FAVORABLE CONDITIONS. 
   C. IN THE EXTENDED FORECAST, THE SYSTEM WILL ACCELERATE WESTWARD 
AND GRADUALLY WEAKEN AS IT INTERACTS WITH HAINAN ISLAND AND EASTERN 
VIETNAM. DUE TO THE COMPLEX STEERING ENVIRONMENT AND DYNAMIC 
SYNOPTIC PATTERN, THERE IS MODERATE CONFIDENCE IN THE JTWC 
FORECAST TRACK.//
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