WDPN31 PGTW 112100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 03W (GUCHOL) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.7N 135.2E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 565 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 37 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY WEAKENING AND INCREASINGLY RAGGED CENTRAL DENSE OVERCAST
(CDO) OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). A LACK OF
RECENT HIGH-RESOLUTION MICROWAVE IMAGERY HAS COMPLICATED PLACEMENT
OF THE LLCC, BUT AS THE CDO GETS PUSHED OFF TO THE EAST BY THE
MODERATE WESTERLY SHEAR, THE OUTER SPIRAL BANDS ARE EMERGING TO THE
WEST, PROVIDING SOME ADDITIONAL CLARITY TO LLCC POSITION. THE
INITIAL INTENSITY AT 1200Z HAS BEEN ADJUSTED 10 KNOTS LOWER AND THE
18Z INITIAL INTENSITY IS THUS COMING MORE IN LINE WITH THE
SUBJECTIVE AND OBJECTIVE FIXES. CONFIDENCE REMAINS MEDIUM AS THERE
REMAINS A FAIRLY LARGE SPREAD IN THE FIX ESTIMATES, BUT THE
ASSESSMENT MOST CLOSELY ALIGNS WITH THE AIDT AND SATCON VALUES AND
ROUGHLY IN THE MIDDLE OF THE AGENCY CURRENT INTENSITY ESTIMATES.
THE SYSTEM IS MOVING RAPIDLY NORTHEAST ALONG THE STRENGTHENING
GRADIENT ON THE WEST SIDE OF THE SUBTROPICAL RIDGE (STR) TO THE
EAST. ANALYSIS REVEALS AN INCREASINGLY UNFAVORABLE ENVIRONMENT,
WITH MODERATE WESTERLY SHEAR, AND MARGINAL SSTS OFFSET BY STRONG
POLEWARD OUTFLOW. THE SYSTEM IS NOW ASSESSED BY BOTH AUTOMATED AND
MANUAL PHASE CLASSIFICATION WORKSHEETS AND THE FSU PHASE SPACE
DIAGRAM, AS HAVING BEGUN SUBTROPICAL TRANSITION (STT).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 62 KTS AT 111634Z
   CIMSS ADT: 47 KTS AT 111740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TS 03W HAS BEGUN SUBTROPICAL
TRANSITION. OTHERWISE, THERE ARE NO MAJOR CHANGES TO THE FORECAST.


FORECAST DISCUSSION: TS 03W HAS PICKED UP SPEED AS THE STEERING
GRADIENT ON THE WEST SIDE OF THE STEERING RIDGE TO THE EAST HAS
STRENGTHENED. NO MAJOR CHANGES TO THE STEERING MECHANISM ARE
ANTICIPATED, THUS TS 03W WILL CONTINUE TO ACCELERATE ON THE
NORTHEASTWARD TRAJECTORY THROUGH THE FORECAST PERIOD. THE SYSTEM
HAS ALREADY BEGUN TO WEAKEN FAIRLY QUICKLY, UNDER THE INFLUENCE OF
INCREASING WESTERLY SHEAR, WHICH IS INDUCING SIGNIFICANT DOWNSHEAR
TILT (TOWARDS THE EAST) AND DECREASING SSTS, NOW BARELY 26C. SHEAR
IS EXPECTED TO DO NOTHING BUT INCREASE FROM HERE ON OUT, AND THE
EXPECTATION IS THAT TS 03W WILL SOON BE DECAPITATED. AS MENTIONED
ABOVE, AUTOMATED AND MANUAL PHASE WORKSHEETS INDICATE THE SYSTEM
HAS ALREADY STARTED STT AND IT IS EXPECTED TO COMPLETE THIS PROCESS
WITHIN THE NEXT 12 HOURS AS IT RAPIDLY MOVES NORTH INTO COOLER
WATERS AND LOSES THE DEEP WARM-CORE VORTEX. BY TAU 24, THE REMNANT
LOW-LEVEL VORTEX WILL COME INTO PHASE WITH A 500MB SHORTWAVE TROUGH
MOVING EAST OFF JAPAN, MOVE UNDER A FINGER OF THE POLAR-FRONT JET
AND BEGIN TO ADVECT COOL, DRY AIR ALONG THE ENTIRE WESTERN FLANK,
MARKING THE BEGINNING OF EXTRATROPICAL TRANSITION (ETT). ETT IS
EXPECTED TO BE COMPLETED NO LATER THAN TAU 48. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY TIGHT AGREEMENT, WITH
MINIMAL CROSS- AND ALONG-TRACK SPREAD, LENDING HIGH CONFIDENCE TO
THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS IN GOOD AGREEMENT AS
WELL, WITH STEADY WEAKENING THROUGH THE FORECAST PERIOD, LENDING
HIGH CONFIDENCE TO THIS ASPECT OF THE FORECAST AS WELL. 

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