WDPN31 PGTW 052100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 
017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.7N 148.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 499 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 04W (MUN) WITH CONVECTION RUNNING ALONG THE NORTHERN
SEMICIRCLE, EXTENDING TO THE WESTERN SIDE OF THE PARTIALLY EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC). A SLOT OF DRY AIR IS BEING
ENTRAINED INTO THE CENTER OF THE VORTEX FROM THE SOUTH, WHICH HAS
BEEN HINDERING ANY FURTHER DEVELOPMENT OF THE SYSTEM. THE
ENVIRONMENT IS NOW ANALYZED TO BE MARGINAL DUE TO DRY AIR
CONTINUING TO BE PULLED INTO THE CENTER. OTHER ENVIRONMENTAL FACTORS
ARE FAVORABLE THOUGH, CHARACTERIZED BY MODERATE POLEWARD OUTFLOW,
LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE
TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE PARTIALLY EXPOSED LLCC IN THE ANIMATED EIR IMAGERY.
THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN EXTENSION OF
RIDGING TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 32 KTS AT 051750Z
   CIMSS AIDT: 58 KTS AT 051750Z
   CIMSS DPRINT: 48 KTS AT 051750Z
   CIMSS DMINT: 53 KTS AT 051813Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: NO FURTHER INTENSIFICATION IS
FORECAST TO OCCUR

FORECAST DISCUSSION: TS 04W IS FORECAST TO BEGIN TURNING NORTHWARD
AS RIDGING TO THE EAST BUILDS IN NEXT TO THE VORTEX. A NORTHWARD
TRACK IS FORECAST TO CONTINUE THOUGH TAU 24 BEFORE A TURN BACK TO
THE NORTH-NORTHWEST BEGINS, IN RESPONSE TO THE FURTHER DEVELOPMENT
OF THE RIDGE. 04W IS THEN FORECAST TO ROUND THE RIDGE AXIS NEAR TAU
48 AND ACCELERATE TO THE NORTHEAST THROUGH TAU 72. SUBTROPICAL
TRANSITION IS FORECAST TO BEGIN AT TAU 48 AND BE COMPLETE BY TAU 72
AS THE VORTEX ENTERS COOLER WATERS AND BECOMES COMPLETELY ENGULFED
BY DRY AIR. 04W IS FORECAST TO MAINTAIN INTENSITY THROUGH TAU 24
AS SEA SURFACE TEMPERATURES REMAIN RELATIVELY WARM AND SHEAR
REMAINS LOW. AFTER TAU 24, THESE FACTORS BEGIN TO SIGNIFICANTLY
WORSEN, CAUSING WEAKENING THROUGHOUT THE REMAINDER OF THE FORECAST
PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT WITH A 142 NM CROSS-TRACK SPREAD AT TAU 48. AFTER TAU 48,
MODELS DIVERGE DUE TO DIFFERENCES IN HOW THE SHALLOW VORTEX
INTERACTS WITH THE UPPER-LEVEL ENVIRONMENT. NAVGEM AND GALWEM BOTH
RACE THE VORTEX OFF TO THE NORTHEAST AFTER TAU 48 WHILE THE
REMAINDER OF GUIDANCE SUGGEST A SLOWER TURN TO THE NORTHEAST. THE
JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE, CLOSE TO THE
CONSENSUS THROUGH TAU 48 AND SLOWER THROUGH TAU 72. INTENSITY
GUIDANCE IS NOW SPLIT, WITH SOME MODELS (GFS AND COAMPS TC)
SUGGESTING SLIGHT INTENSIFICATION THROUGH TAU 24 WHILE HAFS-A
SUGGESTS WEAKENING STARTING FROM TAU 0. ALL MODELS AGREE ON
WEAKENING AFTER TAU 24. THE JTWC INTENSITY FORECAST IS PLACED CLOSE
TO THE MULTI-MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD WITH
MEDIUM CONFIDENCE.

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