WDPN31 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (NARI) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.2N 142.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 621 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
IMPROVING TROPICAL CYCLONE STRUCTURE AS DEEP CONVECTION COMBATS
STRONG NORTHWESTERLY VERTICAL WIND SHEAR. THE LOW-LEVEL CIRCULATION
IS PARTIALLY EXPOSED IN THE NORTHWESTERN PERIPHERY. WATER VAPOR
IMAGERY REVEALS STRONG EQUATORWARD OUTFLOW. AN UPPER-LEVEL TROUGH
TO THE NORTHWEST INDUCES STRONG ABOVE 20KT VERTICAL WIND SHEAR
(VWS). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
121623Z GCOM W-1 AMSR2 89GHZ IMAGE CLOSE TO THE ASSESSED POSITION
IN THE AFOREMENTIONED ANIMATED EIR. THE INITIAL INTENSITY OF 35 KTS
IS ASSESSED WITH HIGH CONFIDENCE BASED ON 121623Z GCOM W-1 AMSR2
WIND SPEED DATA REVEALING WEAK 15-20KT WINDS IN THE WESTERN
SEMICIRCLE OF TROPICAL STORM (TS) 06W AND THE STRONGEST 30-35KT
WINDS IN THE EASTERN PORTION.

INITIAL WIND RADII BASIS: 121623Z GCOM W-1 AMSR2 WIND SPEED DATA

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 41 KTS AT 121620Z
   CIMSS ADT: 35 KTS AT 121730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 06W WILL CURVE NORTHWARD OVER THE NEXT 12
HOURS AS THE STR BUILDS AND BECOMES A STRONGER STEERING INFLUENCE.
THE SYSTEM WILL CONTINUE TO TRACK NORTHWARD FROM TAU 12-36 ON THE
WESTERN PERIPHERY OF THE STR. BETWEEN TAU 36-48, TS 06W IS
ANTICIPATED TO ROUND THE NORTHWESTERN PERIPHERY OF THE STR, ENDING
ON A NORTHEASTWARD TRACK AT TAU 72. EXTRATROPICAL TRANSITION IS
ANTICIPATED TO OCCUR BETWEEN TAU 36-48 AS A LONGWAVE TROUGH CAUSES
THE SYSTEM TO BECOME BAROCLINIC. COOL SEA SURFACE TEMPERATURES WILL
REINFORCE THE TRANSITION AS WELL. TS 06W IS ANTICIPATED TO BECOME
FULLY EXTRATROPICAL BY TAU 48 AND WILL REMAIN IN THAT STATE THROUGH
TAU 72. GRADUAL INTENSIFICATION WILL OCCUR FOR THE FIRST 24 HOURS
OF THE FORECAST AS TS 06W REMAINS IN A MODERATELY FAVORABLE
ENVIRONMENT WITH WARM SEA SURFACE TEMPERATURES, 15-20KT VERTICAL
WIND SHEAR, AND STRONG OUTFLOW. A POLEWARD OUTFLOW CHANNEL IS
ANTICIPATED TO DEVELOP BY TAU 24, ALLOWING FOR A PEAK OF 55KTS.
SLIGHT WEAKENING IS ANTICIPATED AS THE SYSTEM UNDERGOES
EXTRATROPICAL TRANSITION, ULTIMATELY REACHING 25KTS BY THE END OF
THE FORECAST.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TS 06W WILL ASSUME A NORTHWARD TRACK FOR THE NEXT 36-48 HOURS.
ENSEMBLE GUIDANCE HAS A SLIGHT SPREAD, WITH A COUPLE OF WESTERNMOST
MEMBERS TRACKING ALONG THE EASTERN COAST OF JAPAN. THE JTWC TRACK
FORECAST LIES WITHIN THE BULK OF THE MULTI-MODEL CONSENSUS OFFSHORE
OF MAINLAND JAPAN. THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT
INDICATING GRADUAL INTENSIFICATION OVER THE NEXT 24-36 HOURS TO A
PEAK BETWEEN 45-65KTS. THE JTWC INTENSITY FORECAST LIES CLOSE TO
THE MULTI-MODEL CONSENSUS MEAN AS WELL.

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