WDPN32 PGTW 220300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W WARNING NR 21//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
      A. TYPHOON (TY) 11W (VAMCO), LOCATED APPROXIMATELY 570 NM WEST-
NORTHWEST OF WAKE ISLAND, HAS TRACKED NORTHWARD AT 07 KNOTS OVER THE 
PAST SIX HOURS UNDER THE INFLUENCE OF A WESTWARD BUILDING SUB-
TROPICAL RIDGE. ANIMATED MULTISPECTRAL IMAGERY DEPICTS AN ELONGATION
IN THE CENTRAL CONVECTION AROUND AN EYE FEATURE WHICH HAS BECOME
PARTIALLY CLOUD FILLED AND IS ALSO SHOWING SIGNS OF EAST-WEST ELONG-
ATION. INTENSITY ESTIMATES HAVE DECREASED OVER THE PAST 12 HOURS, 
WITH A DVORAK ESTIMATE OF 5.0 FROM PGTW AND 5.5 FROM KNES, INDICATING
APPROXIMATELY 95 KNOTS. UPPER LEVEL OUTFLOW HAS PERSISTED IN THE
POLEWARD CHANNEL HELPING TO MAINTAIN THE CURRENT INTENSITY, HOWEVER
AN UPPER LEVEL TROUGH TO THE NORTH OF TY 11W HAS STARTED TO IMPINGE
ON THE NORTHWARD FLOW IN THE PAST 06 HOURS, SHIFTING A MAJORITY OF
THE OUTFLOW TO THE EASTERN PERIPHERY OF VAMCO. 
3. FORECAST REASONING.
      A. THE FORECAST REASONING FOR INTENSITY HAS CHANGED SLIGHTLY
FROM THE PREVIOUS PROGNOSTIC REASONING BULLETIN DUE TO THE RECENT
WEAKENING NOTED IN PARA. 2.A. THE TRACK PHILOSOPHY HAS REMAINED
UNCHANGED. 
      B. THROUGH TAU 36, VAMCO WILL CONTINUE TO TRACK STEADILY NORTH-
WARD ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL STEERING RIDGE
MENTIONED IN PARA 2.A. IN THE SHORT TERM, VAMCO WILL SLOWLY WEAKEN
OVER THE ENTIRE FORECAST PERIOD AS THE UPPER LEVEL OUTFLOW BECOMES
DISRUPTED BY AN APPROACHING MID-LATITUDE TROUGH. A BRIEF PERIOD OF
INCREASED CONVECTION IS POSSIBLE AS THE MID-LATITUDE TROUGH ENHANCES
THE POLEWARD OUTFLOW PRIOR TO INCREASED VERTICAL WIND SHEAR AS THE
TROUGH MOVES OVER VAMCO. EASTWARD OUTFLOW WILL HELP TO PREVENT QUICK
WEAKENING OF THE SYSTEM THROUGH TAU 36, HOWEVER, BEYOND TAU 36, THE
ENVIRONMENT WILL QUICKLY BECOME UNFAVORABLE FOR TROPICAL DEVELOPMENT.
OCEAN HEAT CONTENT AND SEA SURFACE TEMPERATURES WILL CONTINUE TO
DECREASE AS VAMCO TRACKS NORTHWARD. BETWEEN TAU 48 AND 72 INTERACTION
WITH THE MID-LATITUDE TROUGH WILL BEGIN THE EXTRA-TROPICAL TRANSITION
PROCESS WITH COMPLETE TRANSITION EXPECTED BETWEEN TAU 72 AND 96. THE
TRACK WILL SHIFT TO THE NORTHEAST AS THE SUBTROPICAL RIDGE WEAKENS
ALLOWING VAMCO TO MOVE NORTH OF THE RIDGE AXIS INTO THE MID-LATITUDE
WESTERLIES AND CAUSE IT TO INCREASE SIGNIFICANTLY IN TRACK SPEED.
NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE FORECAST TRACK
AND ASSOCIATED INTENSITY.  
FORECAST TEAM: BRAVO.//
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