WDXS31 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (BIANCA) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.9S 102.0E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 674 NM WEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY WEAKENING SYSTEM, INCREASINGLY BECOMING VERTICALLY
MISALIGNED DUE TO STRONG NORTHWESTERLY SHEAR. AN EARLIER SAR PASS
CONFIRMED THAT THE LOW LEVEL CIRCULATION CENTER (LLCC) IS IN FACT
DISPLACED QUITE A BIT WEST-NORTHWEST OF THE UPPER-LEVEL EYE FEATURE
THAT WAS PRESENT AT THAT TIME AND PROVIDED FOR A HIGH-CONFIDENCE
POSITION UPDATE. WHILE THE FIXES ARE CONTINUING TO TRACK THE
UPPER-LEVEL EYE OR ROTATION, THE INITIAL POSITION IS BEING ASSESSED
MORE ON EXTRAPOLATION OF THE SAR DATA AND PLACED ON THE WESTERN
SIDE OF THE CIRRUS SHIELD USING ANALYSIS OF THE LOWER-LEVEL CLOUD
BANDS EVIDENT IN THE CLEAR AIR TO THE WEST. THE 251134Z SAR PASS
ALSO REVEALED A STRONGER WIND FIELD THAN EARLIER ESTIMATED, WITH A
VMAX OF 106 KNOTS IN THE SOUTHWEST QUADRANT AND 90-95 KNOTS
ELSEWHERE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE, HEDGED TOWARDS THE HIGHER END OF THE OBJECTIVE AND
SUBJECTIVE INTENSITY ESTIMATES NOTED ABOVE, BASED ON THE HIGHER
1200Z INTENSITY ASSESSMENT BASED ON THE SAR. THE ENVIRONMENT IS
UNFAVORABLE, EVEN HOSTILE, WITH COOL SSTS, STRONG NORTHWESTERLY
SHEAR, AND DRY MID-LEVEL INTRUSION OFFSET SLIGHTLY BY THE ROBUST
POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SAR DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 88 KTS AT 251730Z
   CIMSS ADT: 107 KTS AT 251730Z
   CIMSS AIDT: 87 KTS AT 251730Z
   CIMSS D-PRINT: 67 KTS AT 251800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 23-24 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY MID-LEVEL PUNCHING IN FROM THE NORTHWEST. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE WARNING HAS BEEN TRUNCATED TO 36
HOURS. 

FORECAST DISCUSSION: TC 20S (BIANCA) WILL CONTINUE TO TRACK
SOUTH-SOUTHEASTWARD, AS IT SLIDES DOWN THE WEST SIDE OF THE DEEP
RIDGE OVER AUSTRALIA THROUGH THE BULK OF THE FORECAST PERIOD.
FORWARD TRACK SPEEDS ARE EXPECTED TO SLOW DRASTICALLY AFTER TAU 12
AS THE RIDGE SHIFTS EASTWARD AND THE STEERING GRADIENT SLACKENS. TC
20S HAS ALREADY STARTED TO BE SHEARED APART BY THE HIGH SHEAR AND
DRY AIR ENTRAINMENT. THIS PROCESS WILL ONLY ACCELERATE OVER THE
COURSE OF THE NEXT DAY, AND IT IS LIKELY THAT BY TAU 24, ALL THAT
WILL REMAIN WILL BE A NAKED LOW-LEVEL VORTEX AND CIRRUS DEBRIS
RACING POLEWARD. THE SYSTEM WILL RAPIDLY WEAKEN UNDER THESE
UNFAVORABLE CONDITIONS, WHILE ALSO BEGINNING SUBTROPICAL TRANSITION
(STT) WITHIN THE NEXT 6-12 HOURS. AS THE SYSTEM WEAKENS TO JUST 35
KNOTS AND COMPLETES STT BY TAU 36, IT WILL BECOME QUASI-STATIONARY
AS THE STEERING LEVEL DROPS DOWN TO 850MB. THE REMNANT VORTEX WILL
TURN SHARPLY NORTHWESTWARD RIGHT AFTER TAU 36 AS THE STRONG SURFACE
HIGH PRESSURE SYSTEM TO THE SOUTH TAKES OVER THE STEERING
INFLUENCE. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL CONTINUE TO TRACK POLEWARD WHILE SLOWING DOWN
THROUGH THE ENTIRE FORECAST PERIOD. THEY ALSO AGREE THAT THE
REMNANT VORTEX WILL MAKE A VERY SHARP TURN NORTHWESTWARD
IMMEDIATELY AFTER TAU 36. THE MODEL PACKAGE DISPLAYS LITTLE IN THE
WAY OF EITHER ALONG- OR CROSS-TRACK SPREAD, LENDING HIGH CONFIDENCE
TO THE JTWC FORECAST. INTENSITY GUIDANCE IS ALSO IN STRONG
AGREEMENT, WITH ALL CONSENSUS MEMBERS SHOWING RAPID AND PERSISTENT
WEAKENING THROUGH THE FORECAST PERIOD. THE JTWC FORECAST IS SET
SLIGHTLY HIGHER THAN THE CONSENSUS TO ACCOUNT FOR THE HIGHER
STARTING POINT BUT REJOINS THE CONSENSUS MEAN BY THE END OF THE
FORECAST PERIOD. 

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