WDPN31 PGTW 161500
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (HAIYAN) WARNING NR 21//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 161200Z0 TO 191200Z3 OCT 01.
   A. TYPHOON (TY) 25W (HAIYAN), LOCATED APPROXIMATELY 150 NM WEST 
OF OKINAWA, HAS TRACKED NORTH-NORTHEASTWARD AT 09 KNOTS DURING 
THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 161130Z2 
INFRARED SATELLITE IMAGERY AND AVAILABLE SYNOPTIC AND RADAR DATA. 
THE WARNING INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY 
ESTIMATES OF 90 KNOTS. ANIMATED WATER VAPOR IMAGERY REVEALS A SUB-
TROPICAL RIDGE CENTERED EAST OF THE SYSTEM AND AN EASTWARD MOVING 
MID-LATITUDE TROUGH OVER NORTHEASTERN CHINA. IMAGERY ALSO REVEALS A 
LARGE CIRRUS SHIELD FORMING OVER THE PAST 12 HOURS AS THE SYSTEM 
BEGINS TO INTERACT WITH THE MID-LATITUDE WESTERLIES. A DRY SLOT CAN 
ALSO BE SEEN IN THE SOUTHEASTERN QUADRANT OF THE SYSTEM.
   B. TY 25W HAS PASSED NORTH OF THE SUBTROPICAL RIDGE AXIS AND IS 
NOW TRACKING NORTH-NORTHEASTWARD UNDER THE STEERING INFLUENCE OF THE 
MID-LEVEL SUBTROPICAL RIDGE TO THE EAST. THE SYSTEM IS FORECAST TO 
TRACK NORTHEASTWARD THROUGH THE FORECAST PERIOD UNDER THE INFLUENCE 
OF THE SUBTROPICAL RIDGE TO THE EAST-SOUTHEAST AND THE MID-LATITUDE 
WESTERLIES. THE GEOPHYSICAL FLUID DYNAMIC-NAVY (GFDN), JMA GLOBAL 
(JGSM), UK-MET OFFICE (EGRR), NCEP AVIATION (AVN) AND THE COAMPS 
MODEL ARE IN GOOD AGREEMENT INDICATING A NORTHEAST TRACK AND SIMILAR 
SPEEDS OF ADVANCE. THE JMA TYPHOON AND AIR FORCE MM5 MODELS ALSO 
INDICATE A NORTHEAST TRACK BUT DEPICT MUCH FASTER SPEEDS OF ADVANCE. 
NOGAPS INDICATES A MUCH SLOWER SPEED OF ADVANCE AS THE SYSTEM 
WEAKENS RAPIDLY AND FAILS TO BE PICKED UP BY THE MID-LATITUDE 
WESTERLIES. THE FORECAST IS BASED ON PERSISTENCE AND FAVORS THE 
GFDN, JGSM, EGRR, AVN, AND COAMPS CLUSTER. A LOW PROBABILITY 
SCENARIO EXISTS IN THAT THE SYSTEM WOULD WEAKEN MORE RAPIDLY THAN 
THE MODELS INDICATE. THIS SCENARIO WOULD CAUSE TY 25W TO BECOME 
QUASI-STATIONARY AND LOOP BACK TO THE SOUTH BETWEEN THE 24 TO 36 
HOUR PERIOD UNDER THE STEERING INFLUENCE OF THE LOW-LEVEL RIDGE OVER 
EASTERN CHINA. THIS SCENARIO FAVORS THE NOGAPS SOLUTION.
   C. TY 25W IS EXPECTED TO WEAKEN AS IT ENCOUNTERS INCREASING 
VERTICAL WIND SHEAR AND DRIER NORTHEAST WINDS ASSOCIATED WITH A
MONSOON SURGE.
   D. WIND RADII ANALYSIS IS BASED ON A RECENT QUIKSCAT PASS AND 
SYNOPTIC DATA. FORECAST RADII ARE BASED ON CLIMATOLOGY FOR AN 
AVERAGE SIZE TROPICAL CYCLONE.
FORECAST TEAM: CANTRELL/WAUGAMAN/SCOTT/SHERRY/KUMAGA//