WDPN31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.2N 136.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 405 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) AND SHORTWAVE INFRARED (SWIR)
SATELLITE IMAGERY DEPICT A FULLY EXPOSED, COMPACT LOW-LEVEL
CIRCULATION CENTER (LLCC). DEEP CONVECTION PERSISTS ALONG CONVERGENT 
LOW-LEVEL ASYMPTOTES IN THE SOUTHEASTERN SEMICIRCLE, ORGANIZING INTO 
A CDO-LIKE FEATURE. HOWEVER, THE LLCC REMAINS FULLY DECOUPLED FROM 
THIS DOWN-SHEAR CONVECTIVE CANOPY, WHICH IS DISPLACED SOUTHEASTWARD 
BY MODERATE-TO-HIGH (20-25 KT) NORTHWESTERLY VERTICAL WIND SHEAR 
(VWS). SYNOPTICALLY, THE SOUTHWESTERN EXTENT OF A STATIONARY FRONTAL 
BOUNDARY LIES APPROXIMATELY 120 NM NORTH OF THE LLCC. ALOFT, A BROAD 
200MB ANTICYCLONE IS POSITIONED SOUTH OF SHANGHAI, WHILE A 
SOUTHWESTERLY JET STREAM OVERLIES MAINLAND JAPAN AND EXTENDS OUT OVER 
THE PACIFIC NORTHEAST OF HOKKAIDO. A 291007Z SSMIS 91GHZ MICROWAVE 
PASS CLEARLY RESOLVED THE SHALLOW LOW-LEVEL CURVED BANDING WRAPPING 
INTO THE EXPOSED CENTER, WITH VIGOROUS CONVECTIVE ACTIVITY RESTRICTED 
ENTIRELY TO THE DOWN-SHEAR SOUTHEASTERN QUADRANT. THE INITIAL 
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC 
RESOLVED IN SWIR/EIR IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE, BIASED SLIGHTLY HIGHER THAN OBJECTIVE SATELLITE 
ESTIMATES (30-41 KTS) IN DEFERENCE TO AGENCY DVORAK CURRENT INTENSITY 
(CI) ESTIMATES AND CONTINUITY WITH EARLIER SCATTEROMETER DATA 
INDICATING A RESILIENT 45-KNOT SURFACE CORE. ENVIRONMENTAL CONDITIONS 
ARE UNFAVORABLE, DOMINATED BY ELEVATED NORTHWESTERLY SHEAR, MARGINAL 
EQUATORWARD OUTFLOW, AND MID-LEVEL DRY AIR ENTRAINMENT. NONETHELESS, 
CONTINUED TRANSIT OVER THE WARM WATERS OF THE KUROSHIO CURRENT (28-
29C) PROVIDES SUFFICIENT SURFACE HEAT FLUX TO SUSTAIN PERSISTENT 
CONVECTIVE ACTIVITY.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 38 KTS AT 291008Z
   CIMSS ADT: 41 KTS AT 291140Z
   CIMSS AIDT: 39 KTS AT 291140Z
   CIMSS D-MINT: 30 KTS AT 291007Z
   CIMSS D-PRINT: 33 KTS AT 291140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: MID-LEVEL DRY AIR INTRUSION.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 48
HOURS. 

FORECAST DISCUSSION: TROPICAL STORM (TS) 25W IS FORECAST TO CONTINUE
TRACKING NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE LOW- 
TO MID-LEVEL STR THROUGHOUT THE FORECAST PERIOD. 25W WILL REMAIN IN 
THE WARM SECTOR SOUTH OF THE QUASI-STATIONARY COASTAL FRONT THROUGH 
TAU 24. BY TAU 36, 25W WILL INTERACT DIRECTLY WITH THE COASTAL 
BAROCLINIC ZONE, PHASE WITH A PROGRESSIVE 500MB SHORTWAVE TROUGH, AND 
MOVE INTO THE RIGHT-ENTRANCE QUADRANT OF A 200MB UPPER-LEVEL JET 
STREAK, TRIGGERING EXTRATROPICAL TRANSITION (ETT). OVER THE 
SUBSEQUENT 12 HOURS, 25W WILL UNDERGO RAPID ETT, STRUCTURALLY 
TRANSFORMING INTO A COLD-CORE, ASYMMETRIC EXTRATROPICAL LOW BY TAU 
48. REGARDING INTENSITY: 25W WILL EXPERIENCE SLIGHT NEAR-TERM 
WEAKENING OVER THE NEXT 12 TO 18 HOURS. HOWEVER, PERSISTENT DOWN-
SHEAR CONVECTIVE PULSES DRIVEN BY WARM SSTS WITHIN THE KUROSHIO 
CURRENT WILL SUSTAIN BORDERLINE TROPICAL STORM FORCE WINDS (35-40 
KTS) THROUGH TAU 36. AS ETT COMMENCES, STRONG BAROCLINIC FORCING 
COUPLED WITH UPPER-LEVEL DIVERGENT VENTILATION WILL ARREST DECAY, 
PROMPTING SECONDARY POST-TRANSITION RE-INTENSIFICATION BY TAU 48. 

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN EXCELLENT AGREEMENT.
CROSS-TRACK DISPERSION REMAINS TIGHT AND CONSISTENT WITH RECENT 
CYCLES, ALTHOUGH GFS AND GEFS ENSEMBLE MEAN TRACKERS EXHIBIT A SLIGHT 
POLEWARD BIAS TOWARD HONSHU FROM TAU 12 TO 24, WHILE THE OPERATIONAL 
GOOGLE DEEPMIND AND DETERMINISTIC ECMWF MAINTAIN A MORE PROGRESSIVE
EAST-NORTHEASTWARD ORIENTATION. CROSS-TRACK SPREAD REMAINS 
APPROXIMATELY 50 NM AT TAU 24 AND 100 NM BY TAU 48. THE JTWC FORECAST 
TRACK FAVORS THE GOOGLE DEEPMIND AND ECMWF DETERMINISTIC TRACKERS 
ALONG THE SOUTHEASTERN BOUNDARY OF THE MULTI-MODEL ENVELOPE WITH HIGH 
CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN SOLID AGREEMENT. 
STATISTICAL DECAY-SHIPS CONTINUES TO ERRONEOUSLY PREDICT SYSTEM 
DISSIPATION (<20 KTS BY TAU 48), A SOLUTION DISCOUNTED OWING TO KNOWN 
DEFICIENCIES IN RESOLVING BAROCLINIC DEVELOPMENT DURING ETT. 
DYNAMICAL AND AI GUIDANCE (GOOGLE DEEPMIND AND GFS) WEAKEN THE 
CYCLONE TO 35 KNOTS BY TAU 12, MAINTAINING A LOW-END TROPICAL STORM 
THROUGH TAU 36 PRIOR TO MODEST BAROCLINIC RECOVERY AT TAU 48. 
MESOSCALE DYNAMICAL MODELS (HAFS-A AND CTCX) COMPRISE THE HIGHER-END 
CLUSTER, BOTTOMING OUT NEAR 40 KNOTS BEFORE RE-INTENSIFYING TO 50-55 
KNOTS BY TAU 48 AS AN EXTRATROPICAL LOW. THE JTWC FORECAST HEAVILY 
LEANS TOWARD A HAFS-A/CTCX BLEND, TEMPERED SLIGHTLY CONSERVATIVE 
REGARDING THE MAGNITUDE OF POST-ETT RECOVERY.

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