WDXS31 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (OLGA) WARNING NR
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.4S 115.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 130 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 21S (OLGA) TRACKING SOUTH-SOUTHWESTWARD ON THE WESTERN
PERIPHERY OF A LOW-LEVEL SUBTROPICAL RIDGE (STR). THE LOW-LEVEL
CIRCULATION CENTER (LLCC) HAS BECOME FULLY EXPOSED AS SCANT
TENDRILS OF CONVECTION SPORADICALLY DRIFT TO THE SOUTHEAST CARRIED
BY 45-50KT VERTICAL WIND SHEAR (VWS). WEAK UPPER-LEVEL OUTFLOW
DRIFTS EASTWARD WHILE EMBEDDED UNDER AN UPPER-LEVEL JET. SEA
SURFACE TEMPERATURES REMAIN FAVORABLE AT 29-30C. THE INITIAL
POSITION WAS ASSESSED WITH HIGH CONFIDENCE BASED ON ANIMATED EIR
DEPICTING A LLCC. THE INITIAL INTENSITY WAS ASSESSED WITH LOW
CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE

CURRENT STEERING MECHANISM: THE WESTERN PERIPHERY OF A LOW-LEVEL
STR TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   APRF: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 45-50 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK EASTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 21S HAS CONTINUED ON A MORE
SOUTH-SOUTHWESTWARD TRACK OVER THE LAST SIX HOURS AND IS FORECAST
TO CONTINUE TO DO SO FOR THE NEXT 24 HOURS. THE SYSTEM WILL REMAIN
UNDER THE STEERING INFLUENCE OF A LOW-LEVEL STR TO THE EAST THAT
WILL LEAD THE SYSTEM IN THE DIRECTION OF THE EXMOUTH PENINSULA,
THOUGH IT MAY BE POSSIBLE TO TRACK FURTHER INLAND DEPENDING ON THE
STRENGTH OF THE NORTH-SOUTH ORIENTATION OF THE RIDGE. THE SYSTEM IS
FORECAST TO CONTINUE TO WEAKEN TO DISSIPATION OF 30KTS OVER THE
NEXT 12 HOURS AND EVEN FURTHER TO 25KTS BY TAU 24.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TC 21S WILL CONTINUE TO TRACK SOUTH-SOUTHWEST OVER THE NEXT 24
HOURS. THE GFS-BASED COAMPS-TC, HAFS-A, AND HWRF ALL FORECAST THE
CYCLONE TO TRACK OVER THE EXMOUTH PENINSULA DIRECTLY, WHILE GFS
REMAINS JUST OFF OF THE WEST COAST OF THE PENINSULA. THE INTENSITY
GUIDANCE OVERWHELMINGLY AGREES THAT TC 21S WILL WEAKEN TO 30KTS IN
12 HOURS AND 25KTS IN 24 HOURS.

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