WDPN31 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.5N 149.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 473 NM EAST-SOUTHEAST OF NARITA AIRPORT
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A NEARLY
FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH
TROPICAL STORM (TS) 04W (MUN), ACCOMPANIED BY WELL-DEFINED, ALBEIT
SHALLOW, CONVECTIVE BANDING FEATURES. PERSISTENT DRY AIR ENTRAINMENT 
HAS INHIBITED THE DEVELOPMENT AND MAINTENANCE OF DEEP CONVECTION, 
THOUGH THE SYSTEM CONTINUES TO EXHIBIT A COHERENT LOW-LEVEL VORTEX 
STRUCTURE, AND SOME STRONGER CONVECTIVE ACTIVITY IS PRESENT WITHIN THE 
SOUTHEASTERN QUADRANT. ENVIRONMENTAL DIAGNOSTICS INDICATE MARGINALLY 
UNFAVORABLE CONDITIONS, INCLUDING INCREASING (20-25 KTS) 
NORTHEASTERLY VERTICAL WIND SHEAR (VWS), PERSISTENT DRY AIR 
ENTRAINMENT, OFFSET BY BORDERLINE WARM (26-27 C) SEA SURFACE 
TEMPERATURES (SST) AND MODERATE EQUATORWARD UPPER-LEVEL OUTFLOW. THE 
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE, SUPPORTED BY 
ANIMATED INFRARED SATELLITE IMAGERY OF THE LLCC. THE INITIAL INTENSITY 
ESTIMATE OF 50 KTS IS ASSIGNED WITH MEDIUM CONFIDENCE, BASED ON A 
SYNTHESIS OF AGENCY SUBJECTIVE DVORAK ESTIMATES AND AUTOMATED FIXES 
LISTED BELOW.

INITIAL WIND RADII BASIS: 061025Z METOP-B ASCAT PASS

CURRENT STEERING MECHANISM: BUILDING RIDGING TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 48 KTS AT 061200Z
   CIMSS ADT: 37 KTS AT 061200Z
   CIMSS AIDT: 39 KTS AT 061200Z
   CIMSS D-MINT: 43 KTS AT 060748Z
   CIMSS D-PRINT: 52 KTS AT 061200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: PERSISTENT AND SIGNIFICANT DRY AIR ENTRAINMENT 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 04W IS PROJECTED TO TRACK NORTH-NORTHWESTWARD 
UNDER THE INFLUENCE OF A STRENGTHENING SUBTROPICAL RIDGE TO THE EAST. 
AROUND TAU 24, THE SYSTEM IS EXPECTED TO BEGIN TURNING NORTHEASTWARD, 
AS IT ROUNDS THE PERIPHERY OF THE RIDGE AND BECOMES EMBEDDED WITHIN 
MID-LATITUDE DEEP-LAYER WESTERLY FLOW SHORTLY AFTERWARD. SUBTROPICAL 
TRANSITION IS ANTICIPATED TO INITIATE NEAR TAU 36, WITH COMPLETION 
LIKELY BY TAU 48. IN TERMS OF THERMODYNAMIC AND DYNAMIC SUPPORT, THE 
SYSTEM CURRENTLY RESIDES IN A MARGINALLY UNFAVORABLE ENVIRONMENT THAT 
IS FORECAST TO BECOME INCREASINGLY HOSTILE. VERTICAL WIND SHEAR IS
EXPECTED TO INCREASE BEYOND 30 KTS WITHIN 6 TO 12 HOURS, WITH DRY
MID TO UPPER TROPOSPHERIC AIR COMPLETELY ENGULFING THE SYSTEM WITHIN 
THE NEXT 36 HOURS. CONCURRENTLY, SST ARE FORECAST TO DECLINE BELOW 20 
C BY THE END OF THE FORECAST PERIOD, COLLECTIVELY RESULTING IN A 
STEADY WEAKENING TREND THROUGH THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS IN STRONG 
CONSENSUS THROUGH TAU 24, WITH ENSEMBLE AND DETERMINISTIC MODEL 
SPREADS CONFINED TO A CROSS-TRACK SPREAD OF 70 NM. BEYOND THIS PERIOD, 
FORECAST DIVERGENCE INCREASES DUE TO VARYING REPRESENTATIONS OF THE 
SYSTEM INTERACTING WITH THE BAROCLINIC ZONE AND ASSOCIATED UPPER-LEVEL 
FLOW. NAVGEM SOLUTION SUGGESTS A MORE RAPID AND TIGHTER RECURVATURE, 
WHILE ECMWF ENSEMBLE AND GFS DETERMINISTIC MODEL DEPICT A MORE GRADUAL 
AND BROADER TURN TOWARD THE NORTHEAST. THE OFFICIAL JTWC FORECAST 
TRACK LIES NEAR THE MULTI-MODEL CONSENSUS AND IS CARRIED WITH MEDIUM 
CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ACROSS ALL 
CONSENSUS MEMBERS, SUPPORTING A FORECAST OF PROGRESSIVE WEAKENING.
ACCORDINGLY, THE JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH
CONFIDENCE THROUGH TAU 48.

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