WDPN31 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 
043//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.3N 153.7E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 247 NM NORTH OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 21 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04W (SINLAKU) IS CHARACTERIZED AS A HYBRID
SUBTROPICAL SYSTEM, TRAVERSING VERY COOL OCEAN WATERS WITH A
SHALLOW VORTEX STRUCTURE OVERLAID BY DRY MID-LEVEL AIR AND UPPER-
LEVEL CONVERGENCE. CURRENT ANALYSIS INDICATES THE SYSTEM HAS COMMENCED
EXTRA-TROPICAL TRANSITION (ETT). ANIMATED SHORTWAVE INFRARED (SWIR)
SATELLITE IMAGERY DEPICTS A FULLY EXPOSED, BROAD, AND ILL-DEFINED
LOW LEVEL CIRCULATION (LLC). SWIR DATA FURTHER REVEALS ACTIVE COLD 
FRONTOGENESIS TO THE SOUTHEAST OF THE LLC, WHILE A PROMINENT DELTA 
RAIN REGION CONSISTING OF STRATIFORM MID- AND UPPER-LEVEL CLOUDS 
COUPLED WITH EMBEDDED CONVECTION TO THE NORTHEAST DELINEATES THE WARM 
FRONTOGENESIS ZONE. COINCIDENT 191004Z AND 191036Z ASCAT-B/C PASSES 
CONFIRM AN ELONGATED LLC WITH A DISTINCT WARM FRONTAL ZONE IN THE 
NORTHEASTERN QUADRANT. MAXIMUM WINDS OF 50-55 KNOTS WERE OBSERVED IN 
THE COLD-AIR ADVECTION REGION TO THE NORTHWEST AND THE WARM-SECTOR TO 
THE SOUTHEAST, PROVIDING HIGH CONFIDENCE IN BOTH THE INITIAL POSITION 
AND INTENSITY. ENVIRONMENTAL CONDITIONS ARE HIGHLY UNFAVORABLE. 
DEFINED BY HOSTILE VWS, SUB-OPTIMAL SSTS, SUBSIDENT DRY AIR 
ENTRAINMENT, AND CONVERGENT UPPER-LEVEL FLOW ALONG THE WESTERN FLANK.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) COMPLEX EXTENDING FROM EAST OF GUAM 
TO SOUTH OF THE ALEUTIAN ISLANDS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T1.5 - 25 KTS
   CIMSS ADT: 25 KTS AT 191130Z
   CIMSS AIDT: 33 KTS AT 191130Z
   CIMSS D-PRINT: 32 KTS AT 191130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 20-21 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: CONVERGENT UPPER-LEVEL FLOW TO THE WEST; DRY
MID-LEVEL AIR ADVECTING OVER THE WESTERN HALF OF THE VORTEX. 

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 UNDERGOING RAPID EXTRA-TROPICAL
TRANSITION (ETT), WITH BAROCLINIC LEAF SIGNATURES AND FRONTOGENESIS
CLEARLY MANIFEST IN SCATTEROMETER AND SWIR SATELLITE IMAGERY.
THE SYSTEM IS ACCELERATING EAST-NORTHEASTWARD ALONG THE NORTHERN
FLANK OF THE STEERING STR. OVER THE NEXT 24 HOURS, THE DEVELOPING
FRONTAL STRUCTURE WILL STRENGTHEN AND ELONGATE ALONG AN EAST-WEST
AXIS, SYNCHRONOUS WITH THE ZONAL STRETCHING OF THE STR. BY TAU 24,
TS 04W WILL TRACK DUE EASTWARD ALONG THE BAROCLINIC BOUNDARY.
NOTWITHSTANDING THE LOSS OF TROPICAL CHARACTERISTICS, RECENT MULTI-
PLATFORM SENSORS (SAR, SCATTEROMETER, AND SMAP) VALIDATE THAT THE 
VORTEX REMAINS MORE ROBUST THAN MOST MODELS SUGGEST, MAINTAINING 
INTENSITY OVER THE LAST 18 HOURS. MARGINAL DECAY IS FORECAST OVER THE 
NEXT 12 HOURS AS SCATTEROMETER TRENDS INDICATE A CONTRACTION OF THE 
50-KNOT WIND FIELD. UPON COMPLETION OF ETT (BY TAU 18-24), THE SYSTEM 
IS EXPECTED TO MAINTAIN 50-KNOT INTENSITY SUSTAINED BY BAROCLINIC 
FORCING.

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY STRONG AGREEMENT, WITH
MINIMAL CROSS- OR ALONG-TRACK SPREAD THROUGH THE SHORT DURATION OF
THE FORECAST. THE JTWC FORECAST IS PLACED NEAR THE MULTI-MODEL
CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE CONTINUES TO
DEPICT A CONSISTENT PATTERN; SHIPS AND COAMPS-TC PROJECT PRECIPITOUS
WEAKENING, WHEREAS HAFS-A PROFFERS A MORE PLAUSIBLE GRADUAL DECAY
SCENARIO. THE JTWC FORECAST IS HEDGED TOWARD THE HAFS-A WITH HIGH
CONFIDENCE. 

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