WDPN31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.6N 136.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 374 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 25W CONTINUES TO WEAKEN. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) THAT IS GRADUALLY BECOMING LESS
WELL-DEFINED, WITH FLARING CONVECTION CONFINED TO THE SOUTHERN
PERIPHERY. A 291242Z PARTIAL ASCAT-C PASS REVEALED AN ASYMMETRIC
WIND FIELD CHARACTERIZED BY GALE-FORCE WINDS IN THE SOUTHERN
SEMICIRCLE AND LIGHTER WINDS TO THE NORTH. THE SCATTEROMETER DATA
ALSO INDICATED THE FORMATION OF A BELT OF 25-KT EASTERLY WINDS OFF
THE SOUTHERN COAST OF HONSHU, LIKELY ASSOCIATED WITH A TIGHTER
PRESSURE GRADIENT INDUCED BY TS 25W PASSING TO THE SOUTH. A JET
STREAM IS POSITIONED OVER THE SEA OF JAPAN, PRODUCING 20-25 KTS OF
NORTHERLY VERTICAL WIND SHEAR (VWS). CONSEQUENTLY, CONVECTION HAS
BEEN UNABLE TO WRAP AROUND THE LLCC, AND DRY AIR CONTINUES TO
ENTRAIN INTO THE CIRCULATION. THESE DETRIMENTAL FACTORS OUTWEIGHT
THE DEVELOPMENTAL POTENTIAL OF THE WARM SEA SURFACE TEMPERATURES
(SST) OF 27-28 DEGREES CELSIUS, RESULTING IN A LARGELY UNFAVORABLE
ENVIRONMENT FOR INTENSIFICATION. THE INITIAL POSITION IS ASSESSED
WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC. THE INITIAL
INTENSITY HAS BEEN LOWERED TO 40 KTS WITH MEDIUM CONFIDENCE BASED
ON THE FALLING SUBJECTIVE AND OBJECTIVE ESTIMATES, WHICH REFLECT
THE CONTINUED DETERIORATION OF THE SYSTEM STRUCTURE.

INITIAL WIND RADII BASIS: PARTIAL SCATTEROMETER DATA

CURRENT STEERING MECHANISM: NORTHWESTERN FLANK OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED EAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS SATCON: 39 KTS AT 291710Z
   CIMSS ADT: 35 KTS AT 291740Z
   CIMSS AIDT: 39 KTS AT 291740Z
   CIMSS D-MINT: 28 KTS AT 291651Z
   CIMSS D-PRINT: 30 KTS AT 291740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THE REMARKABLE WEAKENING FROM 130 KTS TO 40
KTS OVER THE PAST 48 HOURS HAS LED TO A MUCH SHALLOWER SYSTEM. TS
25W IS NOW STEERED BY THE NORTHWESTERN FLANK OF A LOW- TO MID-LEVEL
STR CENTERED NEAR 33N 164E, RATHER THAN BY THE DEEP-LAYER RIDGE
THAT HAD PREVIOUSLY BEEN THE PRIMARY STEERING MECHANISM. THE
NORTHWESTERN PERIPHERY OF THIS SHALLOWER STR PROVIDES A STRONGER
POLEWARD STEERING COMPONENT. AS A RESULT, THE SYSTEM WILL TURN FROM
ITS CURRENT EAST-NORTHEASTWARD MOTION TOWARD THE NORTHEAST THROUGH
TAU 12. THEREAFTER, STRONGER DEEP-LAYER WESTERLIES WILL GRADUALLY
TURN AND ACCELERATE THE SYSTEM EAST-NORTHEASTWARD THROUGH TAU 48.
DURING THE FIRST 12 HOURS, TS 25W WILL REMAIN UNDER MODERATE TO
HIGH VWS ASSOCIATED WITH A JET STREAM OVER THE SEA OF JAPAN. WITH
CONVECTION STRUGGLING TO REBUILD OVER THE CENTER, THE SYSTEM WILL
WEAKEN TO 35 KTS BY TAU 12. THE CURRENT FORECAST HOLDS THE
INTENSITY NEAR 35 KTS FROM TAU 12 TO TAU 36. HOWEVER, A LOWER-END
SCENARIO IN WHICH TS 25W WEAKENS INTO A TROPICAL DEPRESSION BY TAU
12-24 IS POSSIBLE. STRONGER THERMAL ADVECTION, INTERACTION WITH A
MID-LEVEL TROUGH, AND PARTIAL PHASING WITH A MODEST JET STREAK WILL
LEAD TO SLIGHT BAROCLINIC REINTENSIFICATION TOWARD THE END OF THE
FORECAST PERIOD AS THE SYSTEM RAPIDLY UNDERGOES EXTRATROPICAL
TRANSITION.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT. THE
CROSS-TRACK SPREAD REMAINS SMALL, INCREASING FROM 30 NM AT TAU 12
TO 60 NM AT TAU 36. THE ALONG-TRACK SPREAD REMAINS LARGER, WITH
GOOGLE DEEPMIND, ECMWF, AND GALWEM DEPICTING THE FASTER TRACK
SOLUTIONS. THE JTWC FORECAST TRACK IS POSITIONED EQUATORWARD OF THE
JTWC CONSENSUS (CONW), HEDGED TOWARD THE DEEPMIND AND ECMWF
SOLUTIONS. THE INTENSITY GUIDANCE EXHIBITS A VERY SMALL SPREAD OF 5
KTS THROUGH TAU 36. THE RELIABLE AIDS LARGELY DEPICT WEAKENING
THROUGH TAU 12, FOLLOWED BY A NEAR-STEADY INTENSITY OF 30-35 KTS.
DUE TO THE CONTINUED RAPID WEAKENING OF TS 25W, THE JTWC INTENSITY
FORECAST HAS BEEN NUDGED LOWER BUT REMAINS ON THE HIGHER SIDE OF
THE GUIDANCE ENVELOPE. THE SPREAD INCREASES TO NEAR 10 KTS AT TAU
48, WITH DEEPMIND HOLDING THE INTENSITY STEADY WHILE COAMPS-TC,
HAFS-A, GFS, AND ECMWF DEPICT BAROCLINIC REINTENSIFICATION TO 40-45
KTS. THE JTWC INTENSITY FORECAST LEANS TOWARD A BLEND OF GFS AND
ECMWF GLOBAL MODEL SOLUTIONS AT TAU 48.

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