WDXS31 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (BIANCA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.2S 102.9E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 591 NM SOUTHEAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 20S (BIANCA) WITH A 24 NM SLIGHTLY RAGGED EYE AND A MUCH
MORE SYMMETRIC CENTRAL DENSE OVERCAST SURROUNDING THE EYEWALL.
ENVIRONMENTAL ANALYSIS INDICATES THAT 20S IS IN A FAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, LOW
(5-10 KTS) VERTICAL WIND SHEAR, AND WARM (26-27 C) SEA SURFACE
TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE EYE IN ANIMATED EIR SATELLITE IMAGERY. THE INITIAL
INTENSITY OF 95 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   APRF: T4.5 - 77 KTS
   CIMSS SATCON: 86 KTS AT 241453Z
   CIMSS ADT: 92 KTS AT 241800Z
   CIMSS AIDT: 89 KTS AT 241800Z
   CIMSS DPRINT: 84 KTS AT 241800Z
   CIMSS DMINT: 83 KTS AT 241801Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 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: TC 20S IS FORECAST TO CONTINUE TRACKING
SOUTH-SOUTHWESTWARD ALONG THE WESTERN PERIPHERY OF THE STR THROUGH
TAU 24. AFTER TAU 24, THE SYSTEM WILL BEGIN TRACKING MORE SOUTHWARD
AS IT BEGINS TO ROUND THE RIDGE AXIS. 20S IS FORECAST TO BEGIN
SUBTROPICAL TRANSITION NEAR TAU 36 WITH COMPLETION BY TAU 48,
POSSIBLY SOONER. REGARDING INTENSITY, 20S IS FORECAST TO HAVE
PEAKED AND WILL BEGIN WEAKENING AS VERTICAL WIND SHEAR STARTS TO
INCREASE AND SEA SURFACE TEMPERATURES COOL. AT TAU 36, SHEAR IS
EXPECTED TO INCREASE TO ABOVE 30 KTS AND SEA SURFACE TEMPERATURES
DROP TO BELOW 24 C. AS A RESULT, AN INTENSITY OF 55 KTS IS FORECAST
AS THE SYSTEMS COMPLETES SUBTROPICAL TRANSITION.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
WITH THE EXCEPTION OF NAVGEM, WHICH TAKES THE SYSTEM FURTHER
WESTWARD THAN THE REMAINDER OF GUIDANCE. THE JTWC TRACK FORECAST IS
PLACED SLIGHTLY TO THE EAST OF CONSENSUS THROUGH THE ENTIRE
FORECAST PERIOD TO OFFSET NAVGEM. INTENSITY GUIDANCE IS IN MODERATE
AGREEMENT. GFS DEPICTS A MUCH WEAKER VORTEX THAN THE MESOSCALE
MODELS THROUGH TAU 36. HAFS-A ALSO SUGGESTS FURTHER INTENSIFICATION
OVER THE NEXT 12 HOURS, DIFFERING FROM THE REMAINDER OF GUIDANCE.
THE JTWC INTENSITY FORECAST IS PLACED SLIGHTLY BELOW HAFS-A
THROUGHOUT THE FORECAST PERIOD WITH MEDIUM CONFIDENCE.

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