WDPN31 PGTW 310300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
030//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.0N 142.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 357 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 12W HAS ACCELERATED POLEWARD AND INTENSIFIED SLIGHTLY OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS CONVECTIVE BANDING PERSISTING OVER THE WESTERN PORTION OF
THE CIRCULATION, SHALLOW BANDING OVER THE EASTERN PORTION, AND A
CLEAR CENTER. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON MULTI-AGENCY SATELLITE FIXES AND RECENT MICROWAVE
SATELLITE IMAGERY INCLUDING 302053Z SSMIS AND 302118Z WSF-M PASSES.
THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH HIGH CONFIDENCE
BASED ON A CONSENSUS OF RECENT AGENCY SUBJECTIVE DVORAK AND
AUTOMATED INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: 302015Z RCM-1 SAR PASS, 302340Z AND
310029Z PARTIAL ASCAT PASSES

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 32 KTS AT 302030Z
   CIMSS AIDT: 42 KTS AT 302030Z
   CIMSS D-MINT: 48 KTS AT 302112Z
   CIMSS D-PRINT: 50 KTS AT 310020Z

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: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE SYSTEM IS EXPECTED TO INTENSIFY
SLIGHTLY MORE IN THE NEAR-TERM THAN REFLECTED IN THE PREVIOUS
FORECAST. HOWEVER, THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST
FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 12W WILL CONTINUE TO TRACK
NORTH-NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF THE CURRENT
SUBTROPICAL STEERING RIDGE THROUGH THE NEXT 36 HOURS. THEREAFTER, A
DEVELOPING SHORTWAVE TROUGH WILL WEAKEN THE STEERING RIDGE AS IT 
OVERTAKES TS 12W FROM THE NORTHWEST, TURNING THE SYSTEM NORTHEASTWARD 
BETWEEN TAU 36 AND 48. AFTER THE TURN, TS 12W WILL ACCELERATE TOWARD 
THE EAST-NORTHEAST AND UNDERGO EXTRATROPICAL TRANSITION AS IT MERGES 
WITH THE MIDLATITUDE WESTERLY FLOW PATTERN. INTERACTION WITH A 
DEVELOPING DISTURBANCE EMBEDDED IN THE MONSOON TROUGH TO THE 
SOUTHWEST COULD DEFLECT STORM MOTION A BIT FARTHER TO THE WEST 
THROUGH TAU 36, ALTHOUGH THIS INTERACTION IS INCREASINGLY UNLIKELY 
GIVEN TRENDS IN THE FLOW PATTERN AND LIMITED EXPECTED NEAR-TERM 
DEVELOPMENT OF THE DISTURBANCE TO THE SOUTHWEST. SLOW TO STEADY 
INTENSIFICATION IS EXPECTED FOR THE NEXT 24 TO 36 HOURS AS THE SYSTEM 
MOVES OVER WARMER WATER BUT OUTFLOW IS RESTRICTED BY UPPER-LEVEL 
TROUGHING JUST TO THE WEST. PEAK INTENSITY IS EXPECTED TO BE A BIT 
HIGHER THAN REFLECTED IN THE PREVIOUS FORECAST GIVEN A SLIGHT 
EASTWARD SHIFT IN THE FORECAST TRACK, WHICH WILL CARRY THE SYSTEM 
OVER WARMER WATER ASSOCIATED WITH THE KUROSHIO CURRENT. IN THE 
EXTENDED PERIOD, INCREASING VERTICAL WIND SHEAR AND PASSAGE OVER 
COOLER WATER WILL WEAKEN THE SYSTEM AS IT UNDERGOES EXTRATROPICAL 
TRANSITION, WHICH IS EXPECTED TO COMMENCE PRIOR TO TAU 96 AND 
COMPLETE BY TAU 120.

MODEL DISCUSSION: CONFIDENCE IN THE NEAR-TERM TRACK FORECAST
CONTINUES TO INCREASE. DETERMINISTIC AND ENSEMBLE MODEL TRACK
FORECAST SOLUTIONS ARE IN BETTER AGREEMENT THROUGH TAU 72, WITH
NEARLY ALL SOLUTIONS NOW KEEPING THE CENTER OF 12W OFFSHORE TO THE
SOUTHEAST OF HONSHU. AVAILABLE INTENSITY FORECAST CONSENSUS
GUIDANCE ALSO AGREES ON A SLOW TO STEADY NEAR-TERM INTENSITY TREND
FOLLOWED BY STEADY WEAKENING IN THE EXTENDED PERIOD PRIOR TO AND
DURING EXTRATROPICAL TRANSITION, WITH COAMPS-TC REGISTERING THE
HIGHEST PEAK OF ABOUT 65 KNOTS IN 24 HOURS. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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