WDPN31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (SAUDEL) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS. 
   TROPICAL STORM (TS) 19W (SAUDEL), LOCATED APPROXIMATELY 123 NM 
NORTH-NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 16 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED SATELLITE IMAGERY 
AND RADAR IMAGERY INDICATE THAT TS 19W'S CENTER IS NOW LOCATED OVER 
WATER WEST OF BAGUIO AFTER TRACKING ACROSS LUZON; CONVECTIVE 
STRUCTURE IS IMPROVING WITH FRAGMENTED BANDING WRAPPING INTO A 
RAGGED LOW LEVEL CIRCULATION CENTER (LLCC). A 201753Z AMSR2 89GHZ 
MICROWAVE IMAGE REVEALS A PARTIALLY EXPOSED, BROAD LLCC WITH 
FRAGMENTED OUTER BANDING AND DISORGANIZED CENTRAL CONVECTION. THE 
INITIAL INTENSITY HAS DECREASED SLIGHTLY TO 40 KNOTS BASED ON DVORAK 
INTENSITY ESTIMATES RANGING FROM T2.5 TO T3.0 (35-45 KNOTS). NEAR-
RADIAL UPPER LEVEL OUTFLOW, LOW (10-15 KT) VERTICAL WIND SHEAR 
(VWS), AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST) 
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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