WDPN32 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (USAGI) WARNING NR 
06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 17W (USAGI), LOCATED APPROXIMATELY 560 NM EAST-
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 03 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
(MSI) SHOWED A SLIGHT WEAKENING OF THE CENTRAL CONVECTION OVER THE 
LOW LEVEL CIRCULATION CENTER (LLCC) IN THE EARLY HOURS OF THE LAST 
FORECAST, BUT THE CORE OF DEEP CONVECTION HAS MADE A RESURGENCE AS 
THE OUTFLOW ALONG THE PERIPHERY HAS BECOME MORE RADIAL IN NATURE 
OVER THE PAST THREE TO SIX HOURS. BROKEN BANDS OF DEEP CONVECTION 
ALONG THE SOUTHERN AND EASTERN PERIPHERY HAVE BEEN BUILDING AS THE 
RADIAL OUTFLOW IMPROVES. THE CURRENT INTENSITY HAS BEEN MAINTAINED 
AT 50 KNOTS AS DVORAK ESTIMATES AND THE CONVECTIVE STRUCTURE OF THE 
SYSTEM HAS REMAINED FAIRLY STEADY OVER THE PAST SIX HOURS. UPPER 
LEVEL ANALYSIS INDICATES THE POINT-SOURCE ANTICYCLONE HAS PERSISTED 
OVER THE LLCC AND HAS BEEN THE PRIMARY FACTOR IN THE RECENT 
IMPROVEMENT OF THE RADIAL OUTFLOW. TS 17W IS SLOWLY TRACKING 
WESTWARD ALONG THE EXTREME SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE 
(STR) THAT EXTENDS FROM CENTRAL CHINA THROUGH THE NORTHWESTERN 
PACIFIC. 
3. FORECAST REASONING.
   A. THE FORECAST TRACK HAS BEEN SHIFTED SOUTHWARD AWAY FROM 
TAIWAN, AS MODEL GUIDANCE HAS CONTINUED TO IMPROVE INDICATING A MORE 
SOUTHERLY TRACK OF THE SYSTEM IN THE EXTENDED TAUS.
   B. TS 17W WILL TRACK WESTWARD UNDER THE INFLUENCE OF THE STR TO 
THE NORTH FOR THE NEXT 24 HOURS UNTIL A MID-LATITUDE TROUGH OVER 
NORTHERN CHINA WEAKENS THE WESTERN EXTENT OF THE STR. THE STR IS NOT 
EXPECTED TO FULLY BREAK DOWN, BUT WILL ALLOW TS 17W TO TURN TO THE 
WEST-NORTHWEST THROUGH TAU 72. FAVORABLE SEA SURFACE TEMPERATURES 
ALONG THE FORECAST TRACK (29 TO 30 CELSIUS) WITH A FAVORABLE UPPER 
LEVEL ENVIRONMENT WILL SUPPORT THE INTENSIFICATION OF THE SYSTEM 
THROUGH TAU 72 TO A PEAK INTENSITY OF 105 KNOTS. 
   C. IN THE EXTENDED TAUS, THE FORECAST TRACK IS EXPECTED TO 
FLATTEN WESTWARD AS THE MID-LATITUDE TROUGH PROPAGATES EASTWARD 
ALLOWING FOR THE STR TO RE-DEVELOP OVER THE SYSTEM. LAND INTERACTION 
WITH TAIWAN FROM TAU 72 THROUGH TAU 96 WILL INTERRUPT THE LOW LEVEL 
FLOW, LEADING TO A WEAKENING TREND THROUGH THE REMAINDER OF THE 
FORECAST. BY TAU 120 SIMILAR LAND EFFECTS WITH COASTAL CHINA WILL 
KEEP TS 17W ON A WEAKENING TREND. MODEL GUIDANCE THROUGH TAU 72 
REMAINS IN GOOD AGREEMENT, LEADING TO HIGH CONFIDENCE IN THE 
SHORT TO MID TERM FORECAST TRACK. OVER THE PAST SIX HOURS MODEL 
GUIDANCE HAS IMPROVED FOR THE EXTENDED FORECAST PERIODS LEADING TO 
HIGH CONFIDENCE IN THE EXTENDED FORECAST TRACK AS WELL.//
NNNN