WDXS31 PGTW 060300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (TWENTYONE) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.8S 120.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 665 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A MEDIUM-SIZED 
SYSTEM THAT CONTINUED TO SLOWLY CONSOLIDATE AND EXPAND WITH FEEDER 
BANDS, ALBEIT STILL FRAGMENTED, WRAPPING TIGHTER TOWARD AN OBSCURED 
LOW LEVEL CIRCULATION CENTER (LLCC). A STRONG POLEWARD OUTFLOW 
PERSISTS AS EVIDENCED BY EXPANSIVE CIRRUS STREAKS ALONG THE
SOUTHERN PERIPHERY. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON A MICROWAVE LLCC FEATURE IN THE 052315Z GPM 37GHZ 
COLOR-ENHANCED IMAGE. THE INITIAL INTENSITY IS PLACED WITH HIGH 
CONFIDENCE BASED ON THE HIGH END OF AGENCY AND AUTOMATED DVORAK 
ESTIMATES AND REFLECTS THE 6-HR CONVECTIVE AND WRAP IMPROVEMENT. 
ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH LOW VWS, STRONG 
OUTFLOW, AND WARM SST SLIGHTLY OFFSET BY DRY AIR INTRUSION AT THE LOW 
LEVELS ALONG THE WESTERN PERIPHERIES.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: PERIPHERY OF NEAR EQUATORIAL RIDGE
(NER) TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   APRF: T2.5 - 35 KTS
   CIMSS ADT: 43 KTS AT 060000Z
   CIMSS AIDT: 40 KTS AT 060000Z
   CIMSS DPRINT: 34 KTS AT 060000Z
   CIMSS DMINT: 35 KTS AT 052313Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 WILL CONTINUE TO TRACK SOUTHWARD THEN
SOUTH-SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE NER AND ITS
SOUTHWEST EXTENSION. AFTER TAU 24, AS THE CYCLONE GRADUALLY
WEAKENS, A LOW LEVEL REFLECTION OF THE SUBTROPICAL RIDGE TO THE
SOUTHEAST WILL ASSUME STEERING AND DRIVE A WEAKER AND SHALLOWER
CYCLONE SOUTHWESTWARD. THE FAVORABLE ENVIRONMENT WILL FUEL
INTENSIFICATION TO A PEAK OF 65KTS BY TAU 24. AFTERWARD, INCREASING
COLD DRY AIR INTRUSION AT THE LOW LEVELS, THEN LATER ON, INCREASING
VWS AS THE CYCLONE APPROACHES THE JET LEVEL WINDS ASSOCIATED WITH
THE PREVAILING WESTERLIES WILL COMBINE TO GRADUALLY WEAKEN THE
SYSTEM LEADING TO DISSIPATION BY TAU 120.  

MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION MODELS ARE IN
OVERALL GOOD AGREEMENT WITH A GRADUAL AND EVEN SPREAD TO 175NM BY
TAU 72, LENDING MEDIUM CONFIDENCE TO THIS PORTION OF THE JTWC TRACK
FORECAST. AFTERWARD, NAVGEM SIGNIFICANTLY DEFLECTS FROM A MORE
SPREAD OUT MAIN PACK TOWARD THE LEFT MARGIN, INCREASING THE
ENVELOPE SPREAD TO OVER 700NM BY TAU 120, AN INDICATION OF A WEAK
VORTEX. THIS LENDS LOW CONFIDENCE TO THE EXTENDED PORTION OF THE
JTWC TRACK FORECAST THAT IS LAID JUST TO THE RIGHT OF CONSENSUS TO
OFFSET NAVGEM.

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