WDXS31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (OLGA) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.6S 116.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 315 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION
DISPLACED TO THE SOUTHEAST AS ELEVATED VERTICAL WIND SHEAR
(25-30KTS) HAS CONTINUED TO WEAKEN TROPICAL CYCLONE (TC) 21S (OLGA)
OVER THE LAST SIX HOURS. DESPITE THE MITIGATING VWS, THE SEA
SURFACE TEMPERATURES (SST) REMAIN FAVORABLE AT 29-30C. STRONG
POLEWARD OUTFLOW IS DEPICTED ON WATER VAPOR IMAGERY AS THE SYSTEM
APPROACHES THE SUBTROPICAL JET TO THE SOUTH. TC 21S HAS CONTINUED
TO TRAVEL WEST-SOUTHWEST ON THE NORTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE TO THE SOUTHEAST. THE INITIAL POSITION WAS
ASSESSED WITH HIGH CONFIDENCE BASED ON ANIMATED MSI. THE INITIAL
INTENSITY WAS ASSESSED WITH LOW CONFIDENCE BASED ON THE AGENCY AND
OBJECTIVE FIXES LISTED BELOW, BEING HELD HIGHER BASED ON A 062148Z
RCM-2 SAR PASS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE NORTHWESTERN PERIPHERY OF AN STR OT
THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 42 KTS AT 090700Z
   CIMSS ADT: 45 KTS AT 090700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 IS FORECAST TO CONTINUE TO TRACK TO THE
SOUTHWEST THROUGH TAU 72 AS IT CONTINUES TO TRACK ON THE
NORTHWESTERN PERIPHERY OF A LOW-LEVEL STR TO THE EAST. THE SYSTEM
IS EXPECTED TO CONTINUE WEAKENING WHILE INUNDATED WITH ELEVATED VWS
REACHING POSSIBLY 75KTS BY TAU 60. VWS WILL CONTINUE TO INTRODUCE
DRY AIR FROM THE NORTHWEST INTO THE VORTEX, FURTHER WEAKENING THE
SYSTEM TO DISSIPATION BY TAU 48. OUTFLOW WILL NOW ASSIST
INTENSIFICATION AS THE SYSTEM BECOMES EMBEDDED IN THE JET TO THE
SOUTH. THE WIND RADII ARE FORECAST TO PERSIST PRIMARILY IN THE
SOUTHERN HEMISPHERE OF THE SYSTEM AS IT WINDS DOWN. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
WITH ONLY A 150NM CROSS-TRACK SPREAD BY TAU 72, CONSISTENTLY
FORECASTING A SOUTHWESTWARD TRACK THROUGH THE END OF THE FORECAST
PERIOD, BANDED BY UKMET ENSEMBLE TO THE NORTH AND GALWEM TO THE
SOUTH. THE JTWC INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE
SYSTEM WILL CONTINUE TO WEAKEN AND FULLY DISSIPATE BETWEEN TAU 24
(JTWC SHIPS GUIDANCE) AND TAU 60 (COAMPS-TC). 

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