WDXS31 PGTW 260900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (BIANCA) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.5S 102.7E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 654 NM WEST-SOUTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN ELONGATED 
AND INCREASINGLY VERTICALLY TILTED TROPICAL CYCLONE (TC) 20S
(BIANCA). STRONG (40-45 KTS) VERTICAL WIND SHEAR, COMBINED WITH THE
COOLING (23-24 C) SEA SURFACE TEMPERATURES (SST) ARE CAUSING THE
SYSTEM TO ERODE. OFFSET ONLY BY THE STRONG, POLEWARD OUTFLOW, THE
SYSTEM DOES NOT HAVE ENOUGH FUEL TO SUSTAIN ITSELF AND IS QUICKLY
HEADING TOWARDS DISSIPATION. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON A FULLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) PRESENT IN THE HIGH RESOLUTION VISIBLE IMAGERY LOOP.
THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE 260232Z METOP-B ASCAT DATA, AS WELL AS THE DVORAK
AGENCY FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: 260232Z SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 260730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 40+ KTS
   SST: 23-24 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORECAST COVERS A 24 HOUR PERIOD DUE
TO UPCOMING DISSIPATION

FORECAST DISCUSSION: TC 20S IS FORECAST TO CONTINUE ON A
SOUTH-SOUTHEASTWARD TRACK ALONG THE WESTERN PERIPHERY OF A STR TO
THE EAST FOR THE NEXT 12 HOURS, WHILE CARRYING SOME REMAINING 
MOMENTUM. AS THE SYSTEM LOSES ITS CONVECTIVE STRUCTURE, IT WILL 
ENCOUNTER A DOMINANT EASTERLY LOW-LEVEL FLOW ASSOCIATED WITH A STRONG 
HIGH PRESSURE SYSTEM TO THE SOUTH. THE NEW STEERING PATTERN WILL PUSH 
THE SYSTEM WEST, WHILE IT COMPLETES DISSIPATION BY TAU 24.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD
AGREEMENT, WITH NEARLY ALL MODELS PREDICTING THE SHIFT IN DOMINANT
STEERING MECHANISM AND A WESTWARD TURN AT TAU 12, WHILE SOME TRACKERS 
(UKMET AND ECMWF ENSEMBLE) LOSE TRACK OF THE VORTEX PRIOR TO TAU 24. 
JTWC TRACK FORECAST IS THEREFORE ASSESSED WITH HIGH CONFIDENCE. ALL 
GUIDANCE IS IN GOOD AGREEMENT IN REGARD TO THE INTENSITY FORECAST AS 
WELL, WITH ALL MODELS DISSIPATING THE SYSTEM BY TAU 24.

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