WDPN31 PGTW 231500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W WARNING NR 14//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 04W (SONGDA), LOCATED APPROXIMATELY 600 NM 
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWEST-
WARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED WATER VAPOR 
IMAGERY SHOWS AN EXCELLENT OUTFLOW CHANNEL ALONG THE NORTHEAST 
PERIPHERY OF THE SYSTEM. HOWEVER, AN UPPER LEVEL TROUGH ALONG THE 
NORTHWEST QUADRANT IS INHIBITING OVERALL DEVELOPMENT. THE INITIAL 
POSITION IS BASED ON A 232212Z SSMIS MICROWAVE EYE FEATURE WITH HIGH 
CONFIDENCE. THE INITIAL INTENSITY IS SUPPORTED BY DVORAK ESTIMATES 
RANGING FROM 40 TO 65 KNOTS FROM PGTW, KNES, AND RJTD. TS O4W IS 
JUST TO THE SOUTH OF AN UPPER LEVEL RIDGE IN AN AREA OF WEAK 
VERTICAL WIND SHEAR (VWS). THE CYCLONE IS BEING STEERED ALONG THE 
SOUTHWEST PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE TO THE 
NORTHEAST. 
3. FORECAST REASONING.
   A. NO CHANGE IN FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC 
REASONING BULLETIN.
   B. TS 04W IS EXPECTED TO TRACK AND DEVELOP SLOWLY OVER THE NEXT 
12-24 HOURS UNTIL THE AFOREMENTIONED TROUGH PASSES TO THE EAST. BY 
TAU 36 AS VWS FURTHER RELAXES, THE SYSTEM WILL COMMENCE RAPID 
INTENSIFICATION OVER THE WARM PHILIPPINE SEA, EXCEEDING TYPHOON 
STRENGTH AS IT APPROACHES THE WESTERN EDGE OF THE STEERING RIDGE. 
THE AVAILABLE NUMERICAL GUIDANCE IS IN TIGHT AGREEMENT WITH WITH 
THIS TRACK FORECAST WITH NOGAPS AS THE LEFT OUTLIER, TAKING THE 
VORTEX  
   C. IN THE EXTENDED TAUS, TS SONGDA IS EXPECTED TO RECURVE EAST OF 
TAIWAN TOWARD JAPAN JUST WEST OF OKINAWA, PEAKING AT 115 KNOTS BY 
TAU 96, AND THEN SLOWLY WEAKEN AS ENVIRONMENTAL CONDITIONS (SST AND 
VWS) BECOME LESS FAVORABLE AS THE SYSTEM CONTINUES TO TRACK MORE 
POLEWARD. THIS RECURVATURE WILL BE INITIATED BY A MID-LATITUDE 
TROUGH APPROACHING FROM THE NORTHWEST AND CURRENTLY OVER EASTERN 
CHINA. NUMERICAL MODEL GUIDANCE IS IN OVERALL GOOD AGREEMENT WITH 
NGPS TO THE LEFT OF THE ENVELOPE. THE JTWC FORECAST IS CONSISTENT 
WITH THE PREVIOUS FORECAST AND CLOSE TO, BUT SLIGHTLY FASTER AND 
JUST TO THE EAST OF MODEL CONSENSUS AFTER TAU 72 TO ACCOUNT FOR 
KNOWN MODEL ERRORS IN A RECURVATURE SCENARIO.//
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