WDPN31 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.3N 147.5E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 340 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) O4W (SINLAKU) CONTINUES TO DETERIORATE WHILE
TRAVERSING POLEWARD. ANIMATED SHORTWAVE INFRARED (SWIR) SATELLITE
IMAGERY DEPICTS A SYMMETRIC LOW LEVEL CIRCULATION CENTER (LLCC), WITH 
THE WESTERN SEMICIRCLE FULLY EXPOSED, CONSTRAINING WEAK CONVECTION
AND MID-LEVEL CLOUD COVER TO THE EASTERN SEMICIRCLE. SWIR AND 
ANIMATED WATER VAPOR IMAGERY INDICATE DIFFLUENT UPPER-LEVEL OUTFLOW 
DIRECTED INTO THE ENTRANCE REGION OF A 130KT MID-LATITUDE JET STREAM 
TO THE NORTHEAST. THE DISTAL END OF A WEAKENING FRONTAL BOUNDARY IS 
ALSO EVIDENT TO THE EAST-NORTHEAST OF THE LLCC. LOW-LEVEL 
STRATOCUMULUS IS ADVECTING SOUTHWARD ALONG THE WESTERN FLANK AND 
RECURVING INTO THE SOUTHERN PERIMETER, INDICATING ENTRAINMENT OF A 
SUBSIDENT, STABLE AIR MASS. COINCIDENT ASCAT-B AND ASCAT-C PASSES AT 
181021Z AND 181056Z REVEALED A WELL-DEFINED LLCC, WITH 55 KNOT WINDS 
OBSERVED IN THE NORTHWEST AND SOUTHEAST QUADRANTS, CONSTITUTING A 
TYPICAL BOWTIE SIGNATURE, SURROUNDED BY AN EXTENSIVE REGION OF GALE-
FORCE WINDS. THIS MULTI-PLATFORM SCATTEROMETRY DATA LENDS HIGH 
CONFIDENCE TO BOTH THE INITIAL POSITION AND INTENSITY. ENVIRONMENTAL 
CONDITIONS REMAIN UNFAVORABLE; VERTICAL WIND SHEAR (VWS) HAS INCREASED 
BEYOND 25 KNOTS, SEA SURFACE TEMPERATURES (SST) ARE DECLINING RAPIDLY, 
AND DRY MID-LEVEL AIR IS EXPANDING INTO THE VORTEX CORE. WHILE 
POLEWARD OUTFLOW REMAINS ROBUST, IT IS INSUFFICIENT TO MITIGATE THESE 
DETRIMENTAL ENVIRONMENTAL FACTORS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 35 KTS AT 181140Z
   CIMSS AIDT: 36 KTS AT 181140Z
   CIMSS D-PRINT: 53 KTS AT 181140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE WESTERN FLANK. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 COMMENCING A NORTHEASTWARD 
ACCELERATION AS A TRANSIENT MID-LATITUDE ANTICYCLONE MOVES EASTWARD, 
RE-ESTABLISHING THE STR TO THE SOUTHEAST AS THE DOMINANT STEERING 
INFLUENCE. OVER THE NEXT 48 HOURS, THE STR WILL REPOSITION 
SOUTHWESTWARD TOWARDS GUAM. THE REMNANT FRONTAL BOUNDARY LOCATED 
NORTHEAST OF TS 04W WILL SIMULTANEOUSLY MIGRATE NORTHWARD WHILE 
ELONGATING ZONALLY. TS 04W WILL UNDERGO RAPID RECURVATURE TO AN 
EASTWARD TRAJECTORY BY THE END OF THE PERIOD, INFLUENCED BY THE STR 
TO THE SOUTHEAST AND FLOW ALONG THE FRONTAL INTERFACE. FORWARD SPEED 
IS ANTICIPATED TO STEADILY INCREASE. THE SYSTEM WILL COMMENCE 
EXTRATROPICAL TRANSITION (ETT) WITHIN THE NEXT 24 HOURS, EVOLVING 
INTO A STRONG GALE-FORCE POST-TROPICAL LOW BETWEEN TAU 36 AND TAU 48. 
DESPITE MARGINAL SSTS AND INTENSE WESTERLY SHEAR, TS 04W HAS 
MAINTAINED INTENSITY THROUGH MOMENTUM CONSERVATION. SUBSEQUENTLY, THE 
SYSTEM WILL GRADUALLY DECAY THROUGH TAU 36. POST-TAU 36, BAROCLINIC 
FORCING IS EXPECTED TO FACILITATE INTENSITY MAINTENANCE THROUGH THE 
COMPLETION OF ETT.

MODEL DISCUSSION: TRACK GUIDANCE REMAINS STABLE AND EXHIBITS MINIMAL 
CROSS-TRACK UNCERTAINTY, WITH CONSENSUS SPREAD CONFINED TO A 100NM 
ENVELOPE AT TAU 48. ALONG-TRACK UNCERTAINTY IS ELEVATED (190NM 
SPREAD), TYPICAL OF RECURVATURE SCENARIOS. GFS-INITIALIZED AI 
GUIDANCE PERSISTS AS THE POLEWARD AND FASTEST EXTREME, WHILE EGRR 
REMAINS THE EQUATORWARD AND SLOWEST OUTLIER. THE JTWC FORECAST IS 
ALIGNED WITH THE ECMWF AND EXPERIMENTAL AI TRACKERS WITH HIGH 
CONFIDENCE. INTENSITY GUIDANCE REMAINS MIXED; SHIPS INDICATES RAPID 
DISSIPATION, WHEREAS GFS, HAFS-A, HWRF, AND AI-BASED MODELS DEPICT A 
MORE GRADUAL DECAY. NOTABLY, SEVERAL DYNAMICAL MODELS SUGGEST SLIGHT 
RE-INTENSIFICATION AFTER TAU 36 AS THE VORTEX INTERACTS WITH THE 
BAROCLINIC ZONE. THE JTWC FORECAST IS POSITIONED NEAR THE HAFS-A 
SOLUTIONS WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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