WDPN31 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.8N 142.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 300 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING
CONVECTIVE BANDS WRAPPING INTO A BROAD AND WEAK LOW-LEVEL
CIRCULATION CENTER. THE LLCC IS UNIDENTIFIABLE ON EIR, BUT AN
EARLIER 310837Z WSF-M MICROWAVE IMAGER 37GHZ IMAGE REVEALS THE
BROAD WITH FRAGMENTED BANDING ALONG THE SOUTHERN PERIPHERY. WATER
VAPOR IMAGERY REVEALS MODERATE POLEWARD OUTFLOW AND DRY AIR
ENCAPSULATING TROPICAL STORM (TS) 12W. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE A 311148Z METOP-B ASCAT
IMAGE REVEALING THE LOW-LEVEL CIRCULATION CENTER. THE INITIAL
INTENSITY OF 45 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON A
311120Z METOP-B ASCAT IMAGE DEPICTING A MAXIMUM OF 45KTS IN THE
EASTERN PERIPHERY AND WEAKER 35KT WINDS ON THE WESTERN SIDE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT
BETWEEN A WEAKENING SUBTROPICAL RIDGE OVER JAPAN AND AN ELONGATED
RIDGE TO THE SOUTHEAST ENHANCING MONSOONAL FLOW.

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: 34 KTS AT 311130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 12W HAS WEAKLY TRACKED NORTH-NORTHWESTWARD
OVER THE LAST SIX HOURS AND WILL CONTINUE TO DO SO FOR THE NEXT 24
HOURS WHILE REMAINING IN A WEAK STEERING ENVIRONMENT BETWEEN A
SUBTROPICAL RIDGE (STR) TO THE NORTHWEST AND A NEAR EQUATORIAL
RIDGE (NER) TO THE SOUTHEAST. AN APPROACHING DEEP-LAYER TROUGH WILL
BREAK DOWN THE STR FROM TAU 12-36, RESULTING IN TS 12W TO CURVE TO
THE NORTHEAST FOR THE REMAINDER OF THE FORECAST PERIOD. THE
DEEP-LAYER TROUGH WILL BEGIN TO INTERACT WITH TS 12W AFTER TAU 48
AS THE SYSTEM ENTERS THE BAROCLINIC ZONE AND BECOMES FULLY
EXTRATROPICAL BY TAU 96. DURING THE FIRST 24 HOURS OF THE FORECAST
TS 12W WILL INTENSIFY TO A PEAK OF 60KTS WHILE TRACKING OVER A WARM
EXTENSION OF THE KUROSHIO CURRENT. DURING THE PERIOD OF
INTENSIFICATION, THE VERTICAL WIND SHEAR WILL REMAIN LOW AND
FAVORABLE, AND THE UPPER-LEVEL ENVIRONMENT WILL REMAIN MARGINALLY
DIVERGENT POLEWARD. DRY AIR WILL CONTINUE TO CONFINE TS 12W AND
INHIBIT STRONGER INTENSIFICATION. AFTER TAU 36, TS 12W WILL PASS
INTO COLD WATERS NORTH OF THE KUROSHIO CURRENT, INITIATING A
WEAKENING TREND. VERTICAL WIND SHEAR WILL INCREASE UNFAVORABLY AS
THE SYSTEM TRACKS NORTHEASTWARD AND BEGINS TO INTERACT WITH THE
APPROACHING UPPER-LEVEL TROUGH. BY THE END OF THE FORECAST PERIOD,
TS 12W WILL WEAKEN TO 30KTS AT AN EXTRATROPICAL CYCLONE.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TS 12W WILL REMAIN IN A WEAK STEERING ENVIRONMENT. THE JTWC
MULTI-MODEL CONSENSUS AND THE ENSEMBLE GUIDANCE (GEFS, ECENS,
COAMPS-TC) HAVE TRENDED AWAY FROM HONSHU OVER THE LAST FEW MODEL
RUNS. HOWEVER, THE COMPETITIVE STEERING ENVIRONMENT AND IRREGULAR
TRACK MOTION LENDS LOW CONFIDENCE TO THE JTWC FORECAST. THERE IS A
LARGER SPREAD IN THE JTWC INTENSITY CONSENSUS MEMBERS, INDICATING
PEAK INTENSITIES BETWEEN 45-65KTS BETWEEN TAU 24-48. THE LARGER
SPREAD IS RELATED TO THE SPEED OF CONSENSUS MEMBER TRACKS, AND THE
FASTER-MOVING MEMBERS PEAK HIGHER THAN SLOWER CONSENSUS MEMBERS,
WHICH ARE MORE LIKELY TO WEAKEN DUE TO UPWELLING.

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