WDXS31 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (OLGA) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.9S 116.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 233 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MOSTLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AS THE DEEP CONVECTIVE
BURST THAT HAD COVERED THE SOUTHERN SEMICIRCLE OVER THE PAST
SEVERAL HOURS HAS BEEN SHEARED OFF TO THE SOUTHEAST AND DECAYED.
THE LOW-LEVEL CIRCULATION HAS ALSO BECOME MORE OBLONG IN VISIBLE
IMAGERY, AND A TONGUE OF STRATUS CLOUDS ASSOCIATED WITH A STABLE
LOW-LEVEL AIR MASS CAN BE SEEN WRAPPING AROUND THE WESTERN
SEMICIRCLE. THE INITIAL INTENSITY IS LOWERED TO 35 KT BASED ON THIS
DEGRADATION IN SATELLITE PRESENTATION, CONSISTENT WITH A SLIGHT
OVERALL DECREASE IN OBJECTIVE SATELLITE INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: SURFACE OBSERVATIONS AND PERSISTENCE

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   APRF: T2.5 - 35 KTS
   CIMSS ADT: 41 KTS AT 092030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY, STABLE AIR MASS TO THE WEST AND NORTH

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: TROPICAL CYCLONE 21S (OLGA) CONTINUES TO TRACK
GENERALLY SOUTHWESTWARD ALONG THE PERIPHERY OF A SUBTROPICAL RIDGE
OVER WESTERN AUSTRALIA, THOUGH THE PAST 6-HOUR MOTION HAS BEEN MORE
SOUTHWARD AND AT A SLOWER PACE THAN FORECAST. THE CYCLONE REMAINS
IN THE DECAY STAGE AND CONDITIONS ARE GROWING MORE HOSTILE, WITH
VERTICAL WIND SHEAR NOW 40 TO 50 KT AND A STABLE AIR MASS WRAPPING
INTO THE LLCC. THE MAXIMUM WIND BAND IN THE SOUTHERN SEMICIRCLE MAY
YET TAKE AT LEAST 12 HOURS TO WEAKEN BELOW GALE FORCE, HOWEVER, AS
FRICTION ONLY GRADUALLY SPINS DOWN THE VORTEX. THE JTWC FORECAST
SHOWS OLGA WEAKENING BELOW WARNING CRITERIA BY 24 HOURS WHEN THE
CENTER IS ABOUT 65 NM NORTH OF LEARMONTH, AUSTRALIA. THE REMNANT
VORTEX WILL CONTINUE TRACKING GENERALLY SOUTHWESTWARD AS IT
WEAKENS, WITH MAXIMUM WINDS LIKELY REMAINING ON THE SOUTH SIDE.
DYNAMICAL MODELS HAVE CONTINUED TO ERR TOO FAR WESTWARD WITH OLGA'S
SHORT-TERM FORWARD MOTION, WITH THE ECMWF, HAFS-A, HWRF, AND
COAMPS-TC MODELS PERFORMING BEST. THE JTWC TRACK FORECAST IS THUS
ABOUT 20 NM SOUTHEAST OF THE MULTI-MODEL CONSENSUS, AND SLIGHTLY
CLOSER TO THE AUSTRALIAN COASTLINE THAN THE PREVIOUS FORECAST. THE
MODEL SPREAD DURING THE 24-36 HOUR PERIOD INCLUDES THE POSSIBILITY
OF THE REMNANT VORTEX MOVING NEAR OR OVER THE EXMOUTH PENINSULA.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS ABOUT 20 NM SOUTHEAST
OF THE MULTI-MODEL CONSENSUS DURING THE 24-36 HOUR PERIOD, AND THE
INTENSITY FORECAST IS SLIGHTLY ABOVE THE MULTI-MODEL CONSENSUS,
PRIMARILY DUE TO THE SHIPS STATISTICAL MODEL SHOWING WEAKENING TOO
RAPIDLY.

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