WDPN31 PGTW 280300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 04W WARNING NR 32//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TYPHOON (TY) 04W (SONGDA), LOCATED APPROXIMATELY 295 NM SOUTH-
WEST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD
AT 16 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE
IMAGERY SHOWS WEAKENING CENTRAL CONVECTION SURROUNDING A 10 NM
DIAMETER EYE. THE CONVECTIVE BANDS HAVE BECOME ELONGATED TO THE
NORTHEAST AS THE SYSTEM BEGINS TO ENCOUNTER INCREASING VERTICAL WIND
SHEAR (VWS) ASSOCIATED WITH THE SUBTROPICAL JET STREAM. THE INITIAL
INTENSITY IS SUPPORTED BY DVORAK ESTIMATES FROM PGTW, KNES, AND
RJTD. TY 04W HAS CRESTED THE WESTERN BOUNDARY OF THE DEEP-LAYERED
SUBTROPICAL STEERING RIDGE TO THE EAST AND BEGUN ACCELERATING
NORTHEASTWARD. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS BETWEEN
THE MID-LATITUDE TROUGH DIGGING IN FROM THE WEST AND A TROPICAL
UPPER TROPOSPHERIC TROUGH TO THE EAST. THESE FEATURES ARE ERODING
SOME OF THE CONVECTION ON BOTH FLANKS OF THE SYSTEM, HOWEVER,
POLEWARD AND EQUATORWARD OUFLOW REMAIN STRONG AND HAVE HELPED
MAINTAIN A RELATIVELY STRONG INTENSITY.
3. FORECAST REASONING.
A. THERE ARE NO SIGNIFICANT FORECAST PHILOSOPHY CHANGES FROM THE
PREVIOUS PROGNOSTIC REASONING BULLETIN.
B. TYPHOON SONGDA IS TRACKING ALONG THE WESTERN BOUNDARY OF A
DEEP-LAYERED STEERING RIDGE TO THE EAST. IT IS EXPECTED TO CONTINUE
ACCELERATING POLEWARD AND EASTWARD AND COMMENCE EXTRA-TROPICAL (XT)
TRANSITION BY TAU 36, BECOMING FULL XT BY TAU 48. THE SYSTEM IS
FORECAST TO STEADILY WEAKEN AS IT ENCOUNTERS INCREASING VWS AND
COOLING SEA SURFACE TEMPERATURES. AVAILABLE NUMERICAL MODEL GUIDANCE
IS IN OVERALL GOOD AGREEMENT WITH MAJORITY OF THE MODEL ENVELOPE,
INCLUDING CONSENSUS, TRACKING THE VORTEX JUST NORTH OF OKINAWA, INTO
SOUTHERN KYUSHU AND THEN ALONG THE PACIFIC COASTAL AREAS OF SHIKUKU
AND HONSHU. THIS TRACK FOREACAST IS TO THE RIGHT OF AND SLIGHTLY
FASTER THAN CONSENSUS TO OFFSET KNOWN MODEL TENDENCIES IN A
RECURVATURE SCENARIO.//
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