WDPN31 PGTW 310300
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (FOUR) WARNING 
NR 006//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 04W (FOUR), LOCATED APPROXIMATELY 698 NM
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 08 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS THE LOW LEVEL CIRCULATION (LLC) HAS BECOME 
PARTIALLY EXPOSED, OFFSETTING AN OTHERWISE DEEPENED CENTRAL 
CONVECTION WITH OVERSHOOTING CLOUD TOPS SLIGHTLY SOUTHWESTWARD. THE 
INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE USING LOW CLOUD 
TRACING INTO THE OBSCURED PORTION OF THE LLC. THE INITIAL INTENSITY 
OF 50KTS IS HEDGED HIGHER THAN AGENCY AND OBJECTIVE DVORAK ESTIMATES 
RANGING FROM 30KTS TO 47KTS TO REFLECT THE SLIGHT 6-HOUR IMPROVEMENT 
OF THE SYSTEM AS EVIDENCED IN THE MSI LOOP AND SUPPORTED BY THE 
ONSET OF FORMATIVE EYE FEATURES IN RECENT MICROWAVE IMAGES. THE 
ENVIRONMENT REMAINS OVERALL FAVORABLE WITH RADIAL OUTFLOW AND WARM 
(30-31C) ALONG-TRACK SST OFFSET BY MODERATE (15-20KT) NORTHEASTERLY 
VERTICAL WIND SHEAR. THE CYCLONE IS TRACKING ALONG THE SOUTHWEST 
PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE 
NORTHEAST. 
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. UNDER THE STEERING INFLUENCE OF THE STR, TS 04W WILL CONTINUE 
TO TRACK NORTHWESTWARD OVER THE WARM PHILIPPINE SEA UP TO TAU 72.  
THE SYSTEM IS FORECAST TO STEADILY INTENSIFY UNDER THE 
AFOREMENTIONED FAVORABLE CONDITIONS AS IT APPROACHES THE RIDGE AXIS, 
PEAKING AT 70KTS BY TAU 72. NUMERICAL MODELS ARE IN GOOD AGREEMENT 
WITH A GRADUAL SPREAD TO 270NM AT TAU 72 AND JGSM THE SOLE OUTLIER 
ON THE RIGHT MARGIN OF THE MODEL ENVELOPE, LENDING FAIR CONFIDENCE 
TO THE JTWC TRACK FORECAST THAT IS LAID JUST TO THE LEFT OF THE 
MODEL CONSENSUS TO OFFSET JGSM.
   C. AFTER TAU 72, TS 04W WILL CREST THE STR AXIS AND TURN 
NORTHWARD THEN ACCELERATE NORTHEASTWARD. THE LOWER VWS UNDER THE STR 
AXIS AND INCREASED POLEWARD OUTFLOW DUE TO THE INITIAL EXPOSURE TO 
THE PREVAILING WESTERLIES MAY INTENSIFY THE CYCLONE FURTHER BY TAU 
78; HOWEVER, AFTERWARD, THE INCREASING VWS AND COOLING SST WILL 
GRADUALLY THEN RAPIDLY ERODE THE SYSTEM DOWN TO 40KTS BY TAU 120. 
CONCURRENTLY AT TAU 120, THE CYCLONE WILL BEGIN EXTRA-TROPICAL 
TRANSITION AS IT ENTERS THE COLD BAROCLINIC ZONE. NUMERICAL MODELS 
REMAIN IN GOOD AGREEMENT, LENDING ALSO FAIR CONFIDENCE IN THE 
EXTENDED PORTION OF THE JTWC FORECAST TRACK.//
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