WDXS31 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (OLGA)       
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.6S 120.2E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 627 NM NORTHEAST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A 
CONSOLIDATING SYSTEM, WITH A DEVELOPING CENTRAL DENSE OVERCAST AND 
WEAK DEVELOPING EYE. A 061053Z SSMIS 91 GHZ MICROWAVE IMAGE REVEALS 
DEEP CONVECTIVE BANDING WRAPPING TIGHTLY INTO A DEFINED LOW-LEVEL 
CIRCULATION CENTER, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH 
CONFIDENCE. ALTHOUGH THERE IS DRY AIR PRESENT OVER THE WESTERN 
PERIPHERY OF THE SYSTEM, THERE IS A DEEP MOIST CORE AS WELL AS ROBUST 
POLEWARD OUTFLOW, LOW VERTICAL WIND SHEAR AND WARM SST VALUES. THE 
INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON 
SUBJECTIVE DVORAK INTENSITY ESTIMATES OF 55 KNOTS FROM ALL AGENCIES. 
CIMSS OBJECTIVE INTENSITY ESTIMATES HAVE INCREASED MARKEDLY, WITH ADT 
AND AIDT ESTIMATES RANGING FROM 49 TO 59 KNOTS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   APRF: T3.5 - 55 KTS
   CIMSS SATCON: 50 KTS AT 060800Z
   CIMSS ADT: 59 KTS AT 061130Z
   CIMSS AIDT: 49 KTS AT 061300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL, WITH ENHANCED POLEWARD OUTFLOW

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 (TC) 21S IS TRACKING SLOWLY 
SOUTHWARD ALONG THE WESTERN PERIPHERY OF THE STR BUT IS EXPECTED TO 
TURN SOUTHWESTWARD TO WEST-SOUTHWESTWARD AFTER TAU 24 ALONG AN 
EXTENSION OF THE STR POSITIONED OVER NORTHWESTERN AUSTRALIA. TC OLGA 
WILL CONTINUE TRACKING GENERALLY WEST-SOUTHWESTWARD THROUGH TAU 96, 
WITH A STRONG HIGH BUILDING TO THE SOUTH. ENVIRONMENTAL CONDITIONS 
WILL REMAIN CONDUCIVE THROUGH TAU 24 ALLOWING FOR A SHORT PERIOD OF 
MODERATE INTENSIFICATION, WITH A PEAK INTENSITY OF 80 KNOTS BY TAU 
24. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO DEGRADE QUICKLY AFTER 
TAU 24, WITH INCREASING VERTICAL WIND SHEAR (VWS) OF 25 KNOTS NEAR 
TAU 24 TO 45 KNOTS BY TAU 72. MID- TO UPPER-LEVEL DRY AIR ENTRAINMENT 
WILL INCREASE SIGNIFICANTLY OVER THE NEXT TWO DAYS, WITH THE SYSTEM 
EMBEDDED WITHIN A VERY DRY, HOSTILE ENVIRONMENT BY TAU 72, WHICH
WILL LEAD TO RAPID WEAKENING AND DISSIPATION BY TAU 96.    

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, WHICH SHOWS A
TRACK RECURVING INTO NORTHWEST AUSTRALIA, NUMERICAL MODEL GUIDANCE IS 
IN FAIR AGREEMENT WITH A 140 NM CROSS-TRACK SPREAD IN SOLUTIONS AT
TAU 72 AND 206 NM AT TAU 96. BOTH THE 060000Z ECMWF ENSEMBLE (EPS) 
AND THE 060600Z GFS ENSEMBLE (GEFS) INDICATE A SIMILAR TRACK SPREAD. 
RELIABLE INTENSITY GUIDANCE CONSISTENTLY INDICATES A SHARP 
INTENSIFICATION TREND THROUGH TAU 24 WITH PEAK INTENSITIES RANGING
FROM 60 TO 80 KNOTS THEN A PERIOD OF RAPID WEAKENING THROUGH TAU
96. RAPID INTENSIFICATION GUIDANCE HAS CONTINUED TO TRIGGER 
SUPPORTING THE SHARP INTENSIFICATION PHASE. THE 060600Z COAMPS-TC 
INTENSITY ENSEMBLE NO LONGER INDICATES RAPID INTENSIFICATION BUT DOES 
SHOW A 40 TO 50 PERCENT PROBABILITY OF MODERATE INTENSIFICATION 
THROUGH TAU 24.  

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