WDXS31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (OLGA) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.6S 118.5E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 423 NM NORTHEAST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS TC 21S
CONTINUED TO SIGNIFICANTLY DEGRADE AS EVIDENCED BY EXCESSIVE
POLEWARD ELONGATION, WARMING CLOUD TOPS, AND CONVECTIVE
FRAGMENTATION MOSTLY DUE TO HIGH (30+ KNOTS) WESTERLY VWS. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A SMALL
CLUSTER OF WARM PIXELS IN THE 072350Z EIR IMAGE, ADJUSTED FOR
TILT, AND LINED UP WITH A SEMI-EXPOSED MICROWAVE LLC FEATURE IN THE
072150Z SSMIS 91GHZ IMAGE. THE INITIAL INTENSITY IS ALSO PLACED
WITH MEDIUM CONFIDENCE BASED ON OVERALL ASSESSMENT OF AGENCY AND
AUTOMATED DVORAK ESTIMATES AND REFLECTS THE RAPID WEAKENING TREND.
ANALYSIS INDICATES AN UNFAVORABLE ENVIRONMENT WITH THE STRONG
POLEWARD OUTFLOW AND WARM SST OFFSET BY STRONG VWS AND DRY AIR
INTRUSION AT THE LOWER LEVELS WRAPPING IN FROM THE SOUTHWEST
PERIPHERIES.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO
THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   DEMS: T6.0 - 115 KTS
   CIMSS ADT: 107 KTS AT 072330Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 OLGA WILL CONTINUE SOUTHWESTWARD ALONG THE
NORTHWEST EDGE OF THE SOUTHWEST EXTENSION OF THE STEERING STR. THE
HIGHLY UNFAVORABLE ENVIRONMENT WILL ONLY GET WORSE WITH INCREASING VWS 
AND COOL DRY AIR INTRUSION. THESE WILL ENHANCE RAPID EROSION LEADING 
TO DISSIPATION BY TAU 96, POSSIBLY SOONER. 

MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION MODELS ARE IN
OVERALL GOOD AGREEMENT WITH AN EVEN BUT INCREASINGLY WIDENING
SPREAD TO 355NM BY TAU 96, LENDING MEDIUM CONFIDENCE TO THE JTWC
TRACK FORECAST. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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