WDPN31 PGTW 302100
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (FOUR) WARNING 
NR 005//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 04W (FOUR), LOCATED APPROXIMATELY 746 NM
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 08 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY (EIR) SHOWS CONTINUING CONSOLIDATION WITH THE CONVECTIVE 
FEEDER BANDS, MOSTLY FROM THE NORTH AND SOUTH, WRAPPING TIGHTER INTO 
A DEFINED LOW LEVEL CIRCULATION (LLC). A 301635Z WATER VAPOR 
SATELLITE IMAGE SHOWS AN IMPRESSIVE RING OF OVERSHOOTING TOPS 
CIRCLING AROUND THE LLC, INDICATING A STRENGTHENING CENTER 
STRUCTURE. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED 
ON LOW CLOUD TRACING IN THE EIR LOOP AND ON AN OBSCURED LLC FEATURE 
IN THE A 301629Z AMSR2 89GHZ MICROWAVE PASS. THE INITIAL INTENSITY 
OF 45KTS IS SET WITH FAIR CONFIDENCE BASED ON AN OVERALL ASSESSMENT 
OF DVORAK ESTIMATES OF T2.5/35KTS (PGTW), T3.1/47KTS (ADT), AND 
SATELLITE CONSENSUS (SATCON) OF 49 KTS. TS 04W REMAINS IN A 
FAVORABLE ENVIRONMENT WITH GOOD EASTWARD AND EQUATORWARD OUTFLOW, 
LOW (10-15KTS) VERTICAL WIND SHEAR (VWS) ALOFT, AND VERY WARM (30-
31C) SEA SURFACE TEMPERATURES (SST) IN THE PHILIPPINE SEA. THE 
CYCLONE IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE SUBTROPICAL 
RIDGE (STR) TO THE EAST-NORTHEAST. 
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 04W WILL CONTINUE TO TRACK NORTHWESTWARD OVER THE NEXT 72 
HOURS UNDER THE STEERING INFLUENCE OF THE STR. THE SYSTEM IS 
FORECAST TO STEADILY INTENSIFY UNDER THE AFOREMENTIONED FAVORABLE 
CONDITIONS AS IT APPROACHES THE RIDGE AXIS. THE FORECAST TRACK IS 
LAID SLIGHTLY TO THE LEFT AND AHEAD OF MODEL CONSENSUS TO OFFSET THE 
JGSM TRACKER BEING SLOW AND TO THE RIGHT OF THE MODEL ENVELOPE. 
AFTER TAU 72, THE FORECAST TRACK IS MORE TO THE RIGHT OF FORECAST 
CONSENSUS TO OFFSET GFS BEING THE EXTREME LEFT OUTLIER WITH A WEST-
NORTHWESTWARD TRACK TOWARD THE NORTHEAST PORTION OF THE PHILIPPINE 
ISLANDS.
   C. AFTER TAU 72, TS 04W WILL CONTINUE ON ITS NORTHWESTWARD TRACK 
UNDER THE SAME STR; HOWEVER, BY TAU 78, THE SYSTEM WILL BEGIN TO 
ROUND THE RIDGE AXIS AND INTENSIFY. THE FAVORABLE CONDITIONS WILL 
PERSIST AND BY TAU 96, TS 04W WILL REACH TYPHOON INTENSITY OF 65KTS. 
AFTERWARD, AS IT BECOMES EXPOSED TO INCREASED POLEWARD OUTFLOW 
ASSOCIATED WITH THE PREVAILING WESTERLIES UNDER THE POLAR FRONT JET, 
THE SYSTEM WILL INCREASE IN TRACK SPEED AND BEGIN EXTRA-TROPICAL 
TRANSITION BY TAU 120. NUMERICAL MODELS REMAIN IN GOOD AGREEMENT, 
LENDING ALSO FAIR CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC 
FORECAST TRACK.//
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