WDPN31 PGTW 171500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 15W (MEGI) WARNING NR 
19//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. SUPER TYPHOON (STY) 15W (MEGI), LOCATED APPROXIMATELY 310 NM 
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-SOUTHWESTWARD AT 
11 KNOTS OVER THE PAST 06 HOURS ALONG THE SOUTHERN PERIPHERY OF THE 
DEEP LAYER SUBTROPICAL RIDGE TO THE NORTH. MEGI HAS INTENSIFIED TO 
THE UPPER REACHES OF SUPER TYPHOON STRENGTH. CURRENT DVORAK EYE 
FIXES FROM PGTW AND RJTD ESTIMATE MAXIMUM SUSTAINED SURFACE WINDS 
HAVE ELEVATED 10 KNOTS FROM THE PREVIOUS FORECAST TO 155 KNOTS. A 
STRENGTHENED POLEWARD OUTFLOW CHANNEL HAS SUPPORTED THIS 
INTENSIFICATION, IN ADDITION TO SUSTAINED EQUATORWARD OUTFLOW INTO A 
TROPICAL UPPER LEVEL TROPOSPHERIC TROUGH CELL TO THE EAST. EYE 
TEMPERATURES HAVE REMAINED STEADY AT AROUND 15 DEG CELCIUS AND THE 
EYE DIAMETER HAS RANGED FROM 20 TO 25 NM. 
3. FORECAST REASONING.
   A. THIS FORECAST REFLECTS A HIGHER INITIAL INTENSITY THAN 
PREVIOUSLY FORECAST.
   B. OUTER RAINBANDS HAVE ALREADY BEGUN TO AFFECT LUZON. THE SYSTEM 
CENTER IS EXPECTED TO TRACK OVER LUZON IN LESS THAN 12 HOURS AND 
WILL WEAKEN CONSIDERABLY OVER THE RUGGED TOPOGRAPHY. IT WILL EMERGE 
INTO THE SOUTH CHINA SEA AROUND 18/12Z, REORGANIZE, AND GRADUALLY 
STRENGTHEN. AROUND THIS TIME THE STEERING RIDGE WILL BEGIN TO WEAKEN 
AND THE SYSTEM WILL SLOW AND TURN NORTH OF WEST TO THE EAST OF 
HAINAN. MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT FROM SIX HOURS 
AGO. GFS REMAINS THE LONE OUTLIER THROUGH THE FIRST 48 HOURS AND 
STALLS THE CYCLONE OFF THE WEST COAST OF LUZON FOR 1 TO 2 DAYS, THEN 
JERKS THE TRACK PECULIARLY NORTHEAST. THE REST OF THE MODEL PACKING 
RIDES THE SOUTHERN PERIPHERY OF THE WEAKENING/RETREATING STEERING 
RIDGE TO THE WEST THEN NORTHWEST, TO INCLUDE NOGAPS.  
   C. IN THE EXTENDED FORECAST MEGI WILL TURN TOWARDS A BUILDING 
WEAKENESS IN THE STEERING RIDGE OVER SOUTHERN CHINA. MODEL FIELDS 
INDICATE A SHORT WAVE TROUGH AS THE SOURCE OF THIS WEAKNESS. THERE 
IS INCREASED UNCERTAINTY IN THE INTENSITY FORECAST GIVEN THE WIDE 
RANGE AMONG THE INTENSITY GUIDANCE. NONTHELESS, THE 15Z JTWC 
FORECAST REMAINS CONSISTENT WITH A REINTENSIFICATION SCENARIO.//
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