WDPN31 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
042//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 39.9N 150.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 441 NM EAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH
TROPICAL STORM (TS) 12W (KROSA). THE INITIAL POSITION IS DETERMINED
WITH HIGH CONFIDENCE BASED ON VISIBLE IMAGERY THAT SHOWS CURVED
CONVECTIVE BANDING FEATURES WRAPPING INTO THE LLCC, ALONG WITH
EVIDENT DRY AIR ENTRAINMENT INHIBITING DEEP CONVECTION NEAR THE
CORE CENTER. ASSESSMENT IS CORROBORATED BY A 030017Z METOP-C ASCAT
PASS SHOWING A SLIGHTLY ELONGATED LLCC. INITIAL INTENSITY IS
ASSESSED AT 50KTS WITH HIGH CONFIDENCE, BASED ON SLIGHTLY DEGRADED
AND BECOMING INCREASINGLY ASYMMETRICAL CONVECTIVE STRUCTURE OF THE
SYSTEM, AS WELL AS SUBJECTIVE DVORAK INTENSITY ESTIMATES, OBJECTIVE
TECHNIQUES, AND THE AFOREMENTIONED ASCAT PASS INDICATING 45-50 KT
WIND VECTORS SOUTH OF THE LLCC. THE SYNOPTIC ENVIRONMENT IS
CHARACTERIZED BY DEGRADING THERMODYNAMIC AND KINEMATIC PARAMETERS,
INCLUDING SEA SURFACE TEMPERATURES (SST) OF 22-23 C, MODERATE
VERTICAL WIND SHEAR (VWS) IN THE 15-20 KTS RANGE, AND DRY MID-LEVEL
AIR BEING ADVECTED INTO THE INNER CORE. UPPER-LEVEL DIVERGENCE IS
BEING SUPPORTED BY ENHANCED POLEWARD OUTFLOW INTO THE MIDLATITUDE
WESTERLIES, WHICH TEMPORARILY MITIGATES THE OVERALL HOSTILITY OF
THE ENVIRONMENT.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 48 KTS AT 030020Z
   CIMSS ADT: 39 KTS AT 030140Z
   CIMSS AIDT: 44 KTS AT 030140Z
   CIMSS D-MINT: 49 KTS AT 022313Z
   CIMSS D-PRINT: 40 KTS AT 030110Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 10-15 KTS
   SST: 22-23 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 12W IS FORECAST TO TRACK EAST-NORTHEASTWARD
UNDER THE STEERING INFLUENCE OF A DEEP-LAYER SUBTROPICAL RIDGE
POSITIONED TO THE SOUTH. THE SYSTEM HAS MIGRATED POLEWARD AND
EASTWARD OF THE KUROSHIO CURRENT, RESULTING IN SHARPLY REDUCED SST.
SIMULTANEOUSLY, INCREASING DEEP-LAYER SHEAR IS BEGINNING TO DISRUPT
THE VORTEX STRUCTURE, CREATING A DECOUPLING TREND BETWEEN THE
LOW-LEVEL AND MID-LEVEL CIRCULATIONS. AS A RESULT, A GRADUAL 
INTENSITY DECAY IS ANTICIPATED, DRIVEN BY CONTINUED INTERACTION WITH 
A BAROCLINIC ENVIRONMENT AND PERSISTENT SHEAR. AROUND TAU 36, THE 
SYSTEM IS EXPECTED TO BEGIN EXTRATROPICAL TRANSITION (ETT), WHICH IS 
FORECAST TO BE CONCLUDED BY TAU 48, WITH MAXIMUM SUSTAINED WINDS 
DECREASING TO 25 KTS AND THE SYSTEM BECOMING EMBEDDED WITHIN THE 
ZONAL WESTERLIES.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE SHOWS FAIR AGREEMENT IN
REGARD TO THE TRACK FORECAST, WITH A MAXIMUM CROSS-TRACK SPREAD OF
APPROXIMATELY 85 NM. ALONG-TRACK SPREAD INCREASES HOWEVER TO 240 NM
AT TAU 48, WITH NAVGEM OFFERING THE SLOWEST SOLUTION AND
DETERMINISTIC GFS BEING THE FASTEST TRACKER. INTENSITY GUIDANCE IS
ALSO IN PRETTY GOOD AGREEMENT, THOUGH COAMPS-TC VERSIONS DRIVEN BY
BOTH GFS AND NAVGEM FIELDS INDICATE MORE RAPID WEAKENING,
SUGGESTING POSSIBLE DISSIPATION AS SOON AS TAU 12. REMAINING
GUIDANCE INDICATES A SLOWER DECLINE. THE JTWC INTENSITY FORECAST IS
THEREFORE ISSUED WITH MEDIUM CONFIDENCE AND ALIGNS CLOSE TO THAT OF
HAFS AND GFS, SLIGHTLY ABOVE THE MULTI-MODEL CONSENSUS.

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