Tropical Cyclone BIANCA (20S)

WTXS31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 20S (BIANCA) WARNING NR 008//
RMKS/
1. TROPICAL CYCLONE 20S (BIANCA) WARNING NR 008    
   03 ACTIVE TROPICAL CYCLONES IN SOUTHIO
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   261800Z --- NEAR 26.6S 104.2E
     MOVEMENT PAST SIX HOURS - 125 DEGREES AT 05 KTS
     POSITION ACCURATE TO WITHIN 030 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   RADIUS OF 034 KT WINDS - 045 NM NORTHEAST QUADRANT
                            100 NM SOUTHEAST QUADRANT
                            065 NM SOUTHWEST QUADRANT
                            050 NM NORTHWEST QUADRANT
   REPEAT POSIT: 26.6S 104.2E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   270600Z --- 26.3S 103.1E
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
    ---
REMARKS:
262100Z POSITION NEAR 26.5S 103.9E.
26FEB25. TROPICAL CYCLONE 20S (BIANCA), LOCATED APPROXIMATELY 599
NM WEST-SOUTHWEST OF LEARMONTH, AUSTRALIA, HAS TRACKED
SOUTHEASTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. THE CURRENT 
POSITION IS SET WITH HIGH CONFIDENCE ON A FULLY EXPOSED LOW-LEVEL 
CIRCULATION EVIDENT IN ENHANCED INFRARED IMAGERY AND A 261455Z METOP-
B ASCAT PASS, WHICH ALSO SUPPORTS THE INTENSITY ESTIMATE OF 35 KNOTS. 
TC 20S IS RAPIDLY WEAKENING AND UNRAVELING UNDER THE DUAL INFLUENCES 
OF VERY STRONG NORTHWESTERLY VERTICAL WIND SHEAR AND PASSAGE OVER 
COOL WATER. THIS IS THE FINAL WARNING ON THIS SYSTEM BY THE JOINT 
TYPHOON WRNCEN PEARL HARBOR HI. THE SYSTEM WILL BE CLOSELY MONITORED 
FOR SIGNS OF REGENERATION. MINIMUM CENTRAL PRESSURE AT 261800Z IS
1005 MB. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 261800Z IS 15 FEET.
REFER TO TROPICAL CYCLONE 22S (GARANCE) WARNINGS (WTXS32 PGTW)
FOR TWELVE-HOURLY UPDATES. REFER TO TROPICAL CYCLONE 23S (HONDE) 
WARNINGS (WTXS33 PGTW) FOR TWELVE-HOURLY UPDATES.//
NNNN

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//
NNNN