WDPN31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.6N 141.7E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 190 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 12W HAS INTENSIFIED STEADILY AND ACCELERATED POLEWARD OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS FLARING CONVECTIVE BANDING WRAPPING AROUND THE NORTHERN AND
WESTERN PERIPHERIES AND A CLEAR CENTER FEATURE. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON A 312330Z PGTW SATELLITE
FIX AND MICROWAVE EYE FEATURES EVIDENT IN 312058Z WSF-M AND 010039Z
GMI 37 GHZ IMAGERY. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF RECENT MULTI-AGENCY
SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES LISTED BELOW.
RECENT MICROWAVE SATELLITE IMAGERY, INCLUDING THE 010039Z GMI PASS,
INDICATES THAT THE CIRCULATION CONTINUES TO TILT SLIGHTLY
NORTHEASTWARD WITH HEIGHT AS IT RESPONDS TO SOUTHWESTERLY FLOW
ASSOCIATED WITH AN UPPER-LEVEL TROUGH TO THE WEST. THIS UPPER-LEVEL
FLOW APPEARS TO BE RESTRICTING CONVECTIVE DEVELOPMENT WITHIN THE
SOUTHERN PORTION OF THE CIRCULATION, BUT WITH MUTED EFFECT ON THE
RECENT INTENSIFICATION TREND.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND 010011Z METOP-B
ASCAT SCATTEROMETER DATA FOR RADII IN THE EASTERN SEMICIRCLE

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS ADT: 35 KTS AT 312040Z
   CIMSS AIDT: 47 KTS AT 312040Z
   CIMSS D-MINT: 48 KTS AT 010038Z
   CIMSS D-PRINT: 49 KTS AT 010020Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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: TS 12W WILL CONTINUE TO TRACK GENERALLY
POLEWARD FOR THE NEXT 12 HOURS UNDER THE STEERING INFLUENCE OF
SUBTROPICAL RIDGING TO THE EAST. THEREAFTER, A DEVELOPING SHORTWAVE
TROUGH WILL OVERTAKE THE TS 12W, AND THE SYSTEM WILL TURN
EAST-NORTHEASTWARD AS IT ROUNDS THE RIDGE AXIS EAST OF HONSHU. TS
12W WILL ACCELERATE ALONG TRACK AFTER TAU 24 AND UNDERGO
EXTRATROPICAL TRANSITION BETWEEN TAUS 48 AND 72 AS IT MERGES WITH
THE MID-LATITUDE WESTERLY FLOW PATTERN. ADDITIONAL INTENSIFICATION
IS LIKELY OVER THE NEXT TWELVE HOURS AS THE SYSTEM MOVES OVER THE
WARM KUROSHIO CURRENT AND POLEWARD OUTFLOW REMAINS FAVORABLE. BY
TAU 24, ALONG TRACK SEA SURFACE TEMPERATURES WILL BE INCREASINGLY
UNFAVORABLE, ARRESTING THE INTENSIFICATION TREND. AFTER TAU 24, A
COMBINATION OF PASSAGE OVER COOLER WATER AND INCREASING VERTICAL
WIND SHEAR WILL RESULT IN STEADY WEAKENING, ALTHOUGH INITIALLY
FAVORABLE BAROCLINIC INFLUENCES DURING EXTRATROPICAL TRANSITION
WILL KEEP ASSOCIATED WINDS ABOVE THE GALE FORCE THRESHOLD.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE MODEL TRACK FORECAST
GUIDANCE REMAINS IN GOOD AGREEMENT REGARDING THE OVERALL SCENARIO
AND ORIENTATION THROUGHOUT THE FORECAST PERIOD. THE ONLY REMAINING
ELEMENTS OF UNCERTAINTY ARE THE POTENTIAL FOR SMALL NEAR-TERM
DEVIATIONS IN THE TRACK AS THE STORM BEGINS TO INTERACT WITH THE
APPROACHING SHORTWAVE TROUGH AND CONTINUES TO UNDERGO INTENSITY
CHANGES. FOLLOWING THE ANTICIPATED TURN, THE MODEL TRACK FORECAST
PACKAGE IS IN VERY GOOD AGREEMENT REGARDING FORWARD SPEED AND THE
DIRECTIONAL COMPONENT IS TIGHTER ON THE LATEST RUN. THE CURRENT
FORECAST LIES IN THE MIDDLE OF THE WELL-PACKED CONSENSUS GROUPING
AND IS CONSISTENT WITH THE PREVIOUS JTWC TRACK FORECAST. INTENSITY
MODELS ARE ONCE AGAIN IN GOOD AGREEMENT REGARDING SLOW BUT STEADY
INTENSIFICATION FOR THE NEXT 12 TO 24 HOURS WITH GRADUAL WEAKENING
THEREAFTER. GIVEN THE RECENT INTENSIFICATION TREND, IT WOULD NOT BE
SURPRISING TO SEE TS 12W GAIN STATUS AS A MINIMAL TYPHOON, ALTHOUGH
THE CONSENSUS INTENSITY SOLUTION INDICATES A PEAK NEAR 60 KNOTS,
CONSISTENT WITH THE CURRENT JTWC INTENSITY FORECAST. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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