WDXS31 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (BIANCA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.0S 103.6E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 562 NM SOUTHEAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LOW-LEVEL
CLOUD BANDING WRAPPING INTO A CLOUD-FILLED RAGGED EYE THAT HAS
DEVELOPED OVER THE LAST SIX HOURS. CIRRUS FILAMENTS EXPAND FROM THE
CENTER OF THE SYSTEM INDICATING RADIAL OUTFLOW, HOWEVER, THE
STRONGEST OUTFLOW REGION IS A POLEWARD OUTFLOW CHANNEL FEEDS INTO
THE SUBTROPICAL JET TO THE SOUTH. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED MSI. THE
INITIAL INTENSITY OF 75 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: 240132Z METOP-B ASCAT DATA 

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE POSITIONED OVER
WESTERN AUSTRALIA.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T5.0 - 90 KTS
   APRF: T4.0 - 65 KTS
   CIMSS SATCON: 66 KTS AT 240242Z
   CIMSS ADT: 55 KTS AT 240530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 20S WILL CURVE SOUTHWARD
ON THE PERIPHERY OF A SUBTROPICAL RIDGE FOR THE REMAINDER OF THE
FORECAST PERIOD. THE ENVIRONMENT WILL BE FAVORABLE FOR DEVELOPMENT
DURING THE FIRST 12 HOURS OF THE FORECAST WITH LOW VERTICAL WIND
SHEAR, WARM SEA SURFACE TEMPERATURES, AND STRONG DIVERGENCE ALOFT.
AN APPROACHING UPPER-LEVEL TROUGH FROM THE WEST WILL INTRODUCE HIGH
VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT BEGINNING AT TAU 36,
INITIATING WEAKENING. THE SYSTEM WILL BECOME EMBEDDED WITHIN THE
UPPER-LEVEL TROUGH AT TAU 36 AND PASS OVER COOL SEA SURFACE
TEMPERATURES BELOW 26 DEGREES, CAUSING SUBTROPICAL TRANSITION TO
COMMENCE. SUBTROPICAL TRANSITION WILL COMPLETE BY TAU 48 AT AN
INTENSITY OF 55KTS. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE CURVED NATURE OF THE SOUTHWARD TRACK IN THE
NEAR-TERM, BUT DOES BIFURCATE BEYOND THE FORECAST PERIOD. THE
INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT THAT THE SYSTEM WILL
INTENSIFY OVER THE COURSE OF THE NEXT 12 HOURS WITH THE EXCEPTION
OF THE GFS SOLUTION, WHICH DEPICTS CONSISTENT WEAKENING FOR THE
REMAINDER OF THE FORECAST. THE DIFFERENCE IS LIKELY ASSOCIATED WITH
A STRONGER INTERPRETATION OF HOW SIGNIFICANT THE DRY AIR
ENTRAINMENT AND VERTICAL WIND SHEAR WILL AFFECT THE CIRCULATION.

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