WDPN31 PGTW 280300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (NESAT) WARNING NR 19//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 20W (NESAT), LOCATED APPROXIMATELY 640 NM EAST-
SOUTHEAST OF HANOI, VIETNAM, HAS TRACKED WEST-NORTHWESTWARD AT 12
KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY
SHOWS THE SYSTEM HAS LOST SOME OF THE CONVECTION ON THE NORTHWEST
QUADRANT DUE TO SUBSIDENCE. HOWEVER, CONVECTIVE BANDING FROM THE
SOUTHERN PERIPHERY REMAINS ROBUST AND TIGHT. THE INITIAL POSITION
WAS BASED ON THE ABOVE ANIMATION AND FROM A MICROWAVE EYE FEATURE
ON A 272218Z SSSMIS PASS. THE INITIAL INTENSITY WAS SUPPORTED BY
SUBJECTIVE DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL
ANALYSIS INDICATES TY 20W IS SOUTH OF A RIDGE AXIS IN AN AREA OF
MODERATE (15-20 KT) VERTICAL WIND SHEAR (VWS). ANIMATED WATER VAPOR
SATELLITE IMAGERY SHOWS GOOD EQUATORWARD OUTFLOW BUT WEAK POLEWARD
OUTFLOW DUE TO SUBSIDENCE CAUSED BY A BUILDING UPPER LEVEL RIDGE TO
THE NORTHWEST. TY 20W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A
DEEP-LAYERED SUBTROPICAL RIDGE TO THE NORTH AND IS EXPTECTED TO
REMAIN ON THIS TRACK FOR THE DURATION OF THE FORECAST. 
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY.
   B. ALONG-TRACK SEA SURFACE TEMPERATURES WELL IN EXCESS OF 28 
CELSIUS AND GOOD EQUATORWARD OUTFLOW WILL OFFSET THE MODERATE VWS 
AND SUBSIDENCE AND PROMOTE SOME INTENSIFICATION OVER THE NEXT 36 
HOURS. AFTER THE SYSTEM CROSSES INTO HAINAN, TYPHOON NESAT WILL
RAPIDLY WEAKEN, DUE TO LAND INTERACTION AND INCREASING VWS, BEFORE
IT MAKES ONE FINAL LANDFALL JUST SOUTHEAST OF HANOI, VIETNAM. THE
AVAILABLE NUMERICAL GUIDANCE IS IN EXCELLENT AGREEMENT, THEREFORE,
THIS TRACK FORECAST IS IN UNISON WITH MODEL CONSENSUS.//
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