WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (BOPHA) WARNING NR 50//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 26W (BOPHA) LOCATED APPROXIMATELY 270 NM WEST-
NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED NORTHEASTWARD AT 08 
KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON 
RECENT SATELLITE FIXES FROM PGTW AND RJTD. THE INTENSITY ESTIMATE OF 
105 KNOTS IS CONSISTENT WITH DVORAK CURRENT INTENSITY ESTIMATES FROM 
THE SAME REPORTING AGENCIES. TY 26W HAS CONTINUED TO TRACK POLEWARD 
INTO AN AREA OF INCREASING WESTERLY VERTICAL WIND SHEAR OVER THE 
PAST 06 HOURS UNDER THE STEERING INFLUENCE OF AN EXTENSIVE 
SUBTROPICAL RIDGE. TY 26W HAS ONLY WEAKENED SLIGHTLY OVER THE PAST 
SIX HOURS IN THE PRESENCE OF INCREASING WESTERLY VERTICAL WIND 
SHEAR. RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A 
SMALL, RAGGED EYE. AN UPPER LEVEL OUTFLOW CHANNEL ORIENTED TO THE 
NORTHEAST OF THE CYCLONE CONTINUES TO PROVIDE STRONG VENTING.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TY 26W WILL CONTINUE TO TURN EASTWARD OVER THE NEXT 24 HOURS 
UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE. INCREASING 
WESTERLY VERTICAL WIND SHEAR WILL RESULT IN STEADY WEAKENING AS THE 
SYSTEM TRACKS EASTWARD THROUGH TAU 36. THEREAFTER, AS THE CYCLONE 
CONTINUES TO WEAKEN, IT IS EXPECTED TO MOVE EQUATORWARD AND WESTWARD 
FOLLOWING THE LOW LEVEL FLOW. THE NUMERICAL MODEL GUIDANCE, WITH THE 
EXCEPTION OF WBAR AND GFS, IS IN FAIR AGREEMENT WITH THE TRACK 
FORECAST THROUGH TAU 72. WBAR DEPICTS AN UNREALISTIC NORTHEASTWARD 
ACCELERATION INTO THE MID-LATITUDE WESTERLY FLOW PATTERN, WHILE THE 
GFS SHOWS THE SYSTEM MAINTAINING A HIGHER INTENSITY AND CROSSING 
INTO NORTHERN LUZON UNDER THE INFLUENCE OF THE DEEP LAYER FLOW. THIS 
TRACK IS POSSIBLE IF THE SYSTEM MAINTAINS A HIGHER INTENSITY THAN 
FORECAST IN THE EARLY TAUS, BUT VERTICAL WIND SHEAR IS EXPECTED TO 
REMAIN HIGH ENOUGH TO WEAKEN THE CYCLONE AND ALLOW IT TURN BACK 
INTO THE CENTRAL SOUTH CHINA SEA BEFORE IT CAN MAKE LANDFALL IN 
LUZON. GIVEN THE SPREAD IN THE MODEL TRACK GUIDANCE AND HIGH TRACK 
DEPENDENCE ON THE INTENSITY, FORECAST CONFIDENCE THROUGH TAU 72 IS 
LOW.
  C. AFTER TAU 72, TY 26W IS EXPECTED TO CONTINUE TRACKING 
SOUTHWESTARD UNDER THE INFLUENCE OF LOW-LEVEL NORTHEASTERLY FLOW AND 
WEAKEN DUE TO ONGOING VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. 
THERE IS CONSIDERABLE UNCERTAINTY IN THE EXTENDED TRACK FORECAST 
GIVEN EXPECTED LOOPING MOTION AND A SPREAD IN ALONG-TRACK FORECAST 
SPEEDS AMONG CONSENSUS MODEL MEMBERS. EXTENDED FORECAST TRACK 
CONFIDENCE REMAINS LOW.//
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