WDPN31 PGTW 151500
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (HAIYAN) WARNING NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 151200Z9 TO 181200Z2 OCT 01.
   A. TYPHOON (TY) 25W (HAIYAN), LOCATED APPROXIMATELY 220 NM SOUTH-
SOUTHWEST OF OKINAWA, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS 
DURING THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 151130Z1 
INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON 
SATELLITE CURRENT INTENSITY ESTIMATES OF 75 AND 90 KNOTS. ANIMATED 
INFRARED SATELLITE IMAGERY DEPICTS A BANDING EYE FEATURE.
   B. A MID-LEVEL SHORTWAVE RIDGE SITUATED OVER THE EAST CHINA SEA  
HAS WEAKENED AND AN APPROACHING MID-LATITUDE TROUGH IS FORECAST TO 
MODIFY THE RIDGE AXIS AS IT PROPAGATES EAST OUT OF MONGOLIA. THE 
SUBTROPICAL RIDGE SYSTEM IS EXPECTED TO SHIFT EQUATORWARD AS THE 
LONGWAVE PATTERN DEEPENS THE WESTERLIES BY THE 36 HOUR POINT. TY 
25W IS EXPECTED TO TURN POLEWARD IN 12 TO 24 HOURS AS A RESULT. LATE 
IN THE PERIOD, THE SYSTEM IS EXPECTED TO TRACK NORTHEASTWARD TOWARD 
SOUTHERN JAPAN. THE DYNAMICAL MODELS ARE GROUPED INTO TWO CLUSTERS. 
THE JMA TYPHOON AND GLOBAL MODELS, UKMET GLOBAL, AND COAMPS INDICATE 
A RECURVE SCENARIO. SPEED DIFFERENCES ARE STILL PRESENT AMONG MODELS 
BUT TO A LESSER EXTENT THAT IN THE PREVIOUS RUN. NOGAPS AND THE NCEP 
AVIATION MODEL INDICATE STRAIGHT RUNS TO THE NORTHWEST AND WEAKENING 
SYSTEMS WHICH APPEARS TO BE EXCESSIVE AT THIS TIME. THE FORECAST IS 
BASED ON PERSISTENCE AND A RECURVATURE SCENARIO (JMA TYPHOON/GLOBAL, 
UKMET GLOBAL, AND COAMPS).
   C. TY 25W IS EXPECTED TO SLOWLY INTENSIFY OVER THE NEXT 12 HOURS. 
AFTERWARD, A WEAKENING TREND IS EXPECTED AS A NORTHEAST MONSOON 
SURGE AND INCREASING VERTICAL WIND SHEAR BEGINS TO AFFECT THE EAST 
CHINA SEA/OKINAWA OPAREA.
   D. WIND RADII ANALYSIS IS BASED ON IMAGERY AND SYNOPTIC DATA. 
FORECAST RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE SIZE TROPICAL 
CYCLONE.
FORECAST TEAM: SMITH/MAYER/TON//
BT
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