WDPN31 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN)          
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.2N 145.3E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 247 NM NORTHEAST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04W HAS MAINTAINED ROBUST EASTWARD OUTFLOW, 
ENHANCED BY A JET AND TUTT CELL TO THE EAST. THE SYSTEM HAS
DEVELOPED LIMITED OUTFLOW OVER THE CORE, WITH PERSISTENT DEEP 
CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE 
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED 
ENHANCED INFRARED SATELLITE IMAGERY, WHICH DEPICTS A COMPACT
CENTRAL DENSE OVERCAST FEATURE AND PARTIALLY EXPOSED LLCC OVER THE
SOUTHWESTERN QUADRANT. THE INITIAL POSITION IS ALSO SUPPORTED BY A
FORTUITOUS 040811Z RCM-1 SAR IMAGE, WHICH SHOWS A WELL-DEFINED
CENTER. THE INITIAL INTENSITY REMAINS ASSESSED AT 55 KNOTS BASED ON
THE RCM-1 DATA, WHICH INDICATED A VMAX OF 54 KNOTS AND THE CIMSS
AIDT ESTIMATE OF 54 KNOTS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE EAST AND SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 46 KTS AT 041133Z
   CIMSS ADT: 37 KTS AT 041130Z
   CIMSS AIDT: 54 KTS AT 041130Z
   CIMSS D-PRINT: 43 KTS AT 041150Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG EASTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 04W IS EMBEDDED WITHIN A REVERSE TROUGH
FORMATION, WITH THE SUBTROPICAL STEERING RIDGE EXTENDING FROM THE
PHILIPPINES NORTHEASTWARD TO THE EASTERN PERIPHERY OF THE SYSTEM.
THIS IS GENERAL STEERING PATTERN WILL STEER THE SYSTEM NORTHEASTWARD 
THROUGH TAU 36 TOWARD A BREAK IN THE STR ASSOCIATED WITH AN UPPER-
LEVEL SHORTWAVE TROUGH. MODEST INTENSIFICATION IS EXPECTED DUE TO 
MARGINAL SST VALUES (24-25C) AND ROBUST OUTFLOW, WITH A PEAK INTENSITY 
OF 70 KNOTS EXPECTED BY TAU 24. AFTER TAU 36, THE TROUGH WILL 
PROPAGATE EASTWARD AND THE STR WILL REBUILD TO THE NORTH, WHICH WILL 
RESULT IN A MORE NORTHWARD TRACK THROUGH TAU 96. AFTER TAU 96, THE 
SYSTEM WILL ROUND THE STR AXIS AND ENCOUNTER SUBTROPICAL WESTERLIES. 
RAPID WEAKENING WILL OCCUR THROUGH THE REMAINDER OF THE PERIOD DUE TO 
COLD SST VALUES AND HIGH (25-40 KNOTS) VERTICAL WIND SHEAR.    

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 36 BUT DIVERGES QUICKLY THROUGH TAU 120. WITH THE
EXCEPTION OF NAVGEM, THE SOLE OUTLIER, THE DETERMINISTIC MODELS
HAVE COME INTO BETTER AGREEMENT, WITH GFS NOW SHIFTING SIGNIFICANTLY 
CLOSER TO THE BULK OF THE GUIDANCE. THE 040600Z GEFS ENSEMBLE 
CONTINUES TO INDICATE A WIDE SPREAD OF SOLUTIONS, WITH THE BULK OF THE 
GUIDANCE WELL EAST OF JAPAN. THE ECENS ENSEMBLE REMAINS IN TIGHTER 
AGREEMENT AND SUPPORTS THE JTWC TRACK FORECAST WITH MEDIUM OVERALL 
CONFIDENCE. RELIABLE INTENSITY GUIDANCE INDICATES A PEAK INTENSITY 
NEAR TAU 24 BUT VARIES SIGNIFICANTLY FROM 58 TO 76 KNOTS. THIS 
REFLECTS THE UNCERTAINTY IN THE JTWC INTENSITY FORECAST, WITH MEDIUM 
OVERALL CONFIDENCE.   

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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