WDPN31 PGTW 251500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 04W WARNING NR 22//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 04W (SONGDA), LOCATED APPROXIMATELY 385 NM 
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD 
AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE 
IMAGERY DEPICTS A 12 NM RAGGED EYE ASSOCIATED WITH A WELL-DEVELOPED 
SYSTEM.  VIGOROUS DEEP CONVECTION EXISTS ON ALL SIDES OF THE LOW 
LEVEL CIRCULATION CENTER (LLCC). TY 04W HAS INTENSIFIED OVER THE 
PAST 12 HOURS IN THE HIGHLY FAVORABLE ENVIRONMENT OF THE PHILIPPINE 
SEA, WHERE SEA SURFACE TEMPERATURES ARE 30-31 DEGREES AND VERTICAL 
WIND SHEAR (VWS) IS 5-10 KNOTS. THE 250000Z UPPER LEVEL STREAMLINE 
ANALYSIS REVEALS A HIGHLY DIFFLUENT UPPER LEVEL WIND FIELD AND 
ANIMATED WATER VAPOR IMAGERY SHOWS STEADILY IMPROVING OUTFLOW. THE 
CURRENT INTENSITY ANALYSIS IS BASED ON SUBJECTIVE DVORAK ESTIMATES 
OF 102 KNOTS FROM PGTW AND KNES. DESPITE THE SWITCH TO INFRARED 
IMAGERY THE POSITION CONFIDENCE REMAINS HIGH DUE TO SONGDA’S 
DISTINCT EYE FEATURE AND A CLEAR MICROWAVE SIGNATURE FROM A 250903Z 
TRMM IMAGE. THE MICROWAVE IMAGERY ALSO REVEALS THAT THE MOST INTENSE 
CONVECTION IS OVER THE SOUTHERN SEMI-CIRCLE OF THE SYSTEM. OVER THE 
PAST 12 HOURS, TY 04W HAS NOW SHOWN CLEAR AND SUSTAINED MOVEMENT TO 
THE NORTHWEST, AROUND THE WESTERN PERIPHERY OF AN ANTICYCLONE 
CENTERED NEAR 20N 140W. 
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY.
   B. TY 04W WILL CONTINUE TO TRACK AROUND THE ANTICYCLONE CURRENTLY 
CENTERED OVER THE NORTHERN MARIANAS. THE ANTICYCLONE IS EXPECTED TO 
BUILD AND SHIFT WESTWARD, DEVELOPING A POLEWARD ORIENTATION, WHICH 
WILL BLOCK THE STORM FROM EASTWARD MOVEMENT. THIS POLEWARD LEG WILL 
KEEP TY 04W IN THE PHILIPPINE SEA, WHERE THE LOW VWS AND FAVORABLE 
OCEANOGRAPHIC CONDITIONS WILL ALLOW FOR CONTINUED INTENSIFICATION. 
TY 04W SHOULD REACH PEAK INTENSITY JUST AS IT CROSSES THE AXIS OF 
THE SUB-TROPICAL RIDGE AXIS, AT APPROXIMATELY 20 DEGREES NORTH 
LATITUDE NEAR TAU 48. MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON 
BOTH TRACK AND INTENSITY THROUGH TAU 48. AFTER TAU 48, TY 04W WILL 
CREST THE RIDGE AXIS AND MAKE A NORTHEASTWARD TURN THROUGH THE 
RYUKUS. SEA SURFACE TEMPERATURES WILL REMAIN FAVORABLE THROUGH 25 
DEGREES NORTH LATITUDE AND WIND SHEAR WILL INCREASE ONLY GRADUALLY, 
HENCE THE STORM WILL ONLY WEAKEN GRADUALLY UNTIL IT IS NORTH OF 
OKINAWA. ONCE NORTH OF OKINAWA, THE COMBINATION OF SHARPLY 
INCREASING VWS AND SHARPLY FALLING OCEAN HEAT CONTENT WILL 
ACCELERATE THE STORM’S DECAY. MODELS REMAIN IN FAIR AGREEMENT 
REGARDING TRACK BUT BEGIN TO DIVERGE ON SPEED AFTER TY 04W MAKES THE 
TURN TO THE NORTHEAST. DUE TO THE PROJECTED STRENGTH OF THE STEERING 
RIDGE, THE JTWC TRACK FORECAST STAYS SLIGHTLY WEST OF CONSENSUS 
THROUGH THE RYUKUS, BETWEEN CONSENSUS AND ECMF.
   C. TY 04W WILL BEGIN TO WEAKEN RAPIDLY ONCE IT BEGINS EXTRA-
TROPICAL TRANSITION NEAR 30 DEGREES NORTH LATITUDE. THE SYSTEM WILL 
ACCELERATE AND WEAKEN IN RESPONSE TO A DEEP MID-LATITUDE SHORT-WAVE 
TROUGH. A 120 KT POLAR FRONT JET WILL MOVE OFF-SHORE OF SOUTHERN 
HONSHU NEAR TAU 96 AND VWS OVER SONGDA WILL EXCEED 50 KNOTS BEFORE 
IT CROSSES 30 DEGREES NORTH LATITUDE. DYNAMIC AIDS ARE IN GOOD 
GENERAL AGREEMENT AS FAR AS THE DEVELOPMENT OF A HIGH-GALE TO STORM 
FORCE LOW SEAWARD OF THE KANTO PLAIN, BUT THERE IS SIGNIFICANT 
DISPARITY IN TIMING. THE JTWC FORECAST OVER THE EXTENDED RANGE IS 
FASTER AND EQUATORWARD OF CONSENSUS.//
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