WDPN31 PGTW 290300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W WARNING NR 22//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 19W HAS CONTINUED TO WEAKEN RAPIDLY OVER
THE PAST 12 HOURS OVER NORTHERN TAIWAN AND HAS ONLY RECENTLY TRACKED
BACK OVER WATER. THE SYSTEM HAS TRACKED GENERALLY NORTHWARD DURING
THE PAST 12 HOURS AFTER A PERIOD OF ERRATIC MOVEMENT, AND HAS
ACCELERATED NORTH-NORTHWESTWARD AT 09 KNOTS OVER THE PAST 06 HOURS.
THE MODELS HAVE REMAINED IN GOOD AGREEMENT THROUGH TAU 36 AND
CONTINUE TO DIVERGE AFTER THIS TIME WHILE REMAINING IN FAIR
AGREEMENT. 
   B. TS 19W IS TRACKING ALONG THE WESTERN PERIPHERY OF THE MID-
LEVEL SUBTROPICAL RIDGE (STR), WHICH IS ORIENTED NORTH-SOUTH UP
TO 30N. THE 28/12Z 500MB ANALYSIS DEPICTED A WEAK FINGER OF THIS
RIDGE EXTENDING WESTWARD TO SHANGHAI, CHINA. THIS IS CURRENTLY
PROVIDING SOME WESTWARD COMPONENT TO THE TRACK. ANIMATED WATER
VAPOR IMAGERY STILL DEPICTS GOOD RADIAL OUTFLOW, ESPECIALLY THE
POLEWARD OUTFLOW WHICH IS TAPPED INTO STRONG MIDLATITUDE WEST-
ERLIES. THE CURRENT POSITION IS BASED PRIMARILY ON RADAR DATA
FROM TAIWAN SO HIGH CONFIDENCE IN THE 6-HOUR MOTION AND POSITION.
THE CURRENT INTENSITY IS ASSESSED LOWER THAN THE ONLY DVORAK
ESTIMATE OF 77 KNOTS FROM RJTD (CI ONLY) BASED ON THE LACK OF
ANY SIGNIFICANT DEEP CONVECTION. SURFACE OBSERVATIONS FROM
RCTP ABOUT 45 NM SSE INDICATE 36G53 AND THE RADAR STILL SHOWS
AN ORGANIZED SYSTEM WITH HEAVY SHOWER BANDING SUPPORTING THE
60 KNOT INTENSITY AND DOWNGRADE TO TS.     
3. FORECAST REASONING.
   A. THE OVERALL TRACK PHILOSOPHY IS UNCHANGED BUT TRACK SPEEDS
WERE INCREASED SIGNIFICANTLY AFTER TAU 48 AS THE SYSTEM MOVES INTO
THE STRONG MIDLATITUDE WESTERLY FLOW.
   B. TS 19W IS FORECAST TO TRACK NORTHWARD TOWARD THE BREAK IN THE
STR AND WILL RE-CURVE SHARPLY EASTWARD UNDER THE MIDLATITUDE WEST-
ERLIES. THE SYSTEM IS EXPECTED TO CONTINUE WEAKENING AS IT
ENCOUNTERS INCREASING VERTICAL WIND SHEAR (VWS) AFTER TAU 48 AND
WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) NEAR THIS TIME. THE
DYNAMIC MODELS ARE IN GOOD AGREEMENT ON THE OVERALL TRACK WITH SOME
MINOR DIFFERENCES IN TRACK SPEED AND TRACK ORIENTATION.       
   C. TS 19W IS FORECAST TO COMPLETE ETT NEAR TAU 90 AND TO
ACCELERATE AND WEAKEN UNDER STRONG WESTERLY FLOW.   
FORECAST TEAM: DELTA// 
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