WDPS31 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10P (NAT) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.9S 159.4W
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 435 NM WEST OF BORA BORA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A MEDIUM-SIZED
SYSTEM EMBEDDED IN THE SOUTH PACIFIC CONVERGENT ZONE THAT IS FAST
APPROACHING THE STRONG WESTERLIES AS EVIDENCED BY TRANSVERSE
BANDING ALONG THE OUTFLOW CIRRUS TO THE SOUTH. THE COLD DENSE OVERCAST 
HAS DEEPENED OVER THE PAST SIX HOURS, PUNCTUATED BY OVERSHOOTING CLOUD 
TOPS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON 
LOW CLOUD TRACING INTO AN OBSCURED CIRCULATION CENTER IN THE MSI LOOP. 
THE INITIAL INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE 
AGGREGATE AGENCY AND AUTOMATED DVORAK ESTIMATES AND REFLECTS THE 6-HR 
CONVECTIVE IMPROVEMENT. ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH 
WARM SST AND STRONG POLEWARD OUTFLOW OFFSET BY MODERATE TO STRONG VWS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) TO THE
NORTH.


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   CIMSS ADT: 49 KTS AT 060540Z
   CIMSS AIDT: 38 KTS AT 060540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-30 KTS
   SST: 30-31 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 NAT WILL CONTINUE ON ITS CURRENT
EAST-SOUTHEASTWARD TRACK UNDER THE STEERING INFLUENCE OF THE NER FOR 
THE REMAINDER OF THE FORECAST. THE MARGINAL ENVIRONMENT WILL
SUSTAIN THE CURRENT INTENSITY, AT BEST, UP TO TAU 12. AFTERWARD,
INCREASING VWS AND DRY AIR ENTRAINMENT AT THE LOW LEVELS WILL
GRADUALLY ERODE THE SYSTEM TO DISSIPATION BY TAU 48 POSSIBLY
SOONER.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH A
GRADUAL AND EVEN SPREAD TO A MERE 64NM BY TAU 48, LENDING HIGH
CONFIDENCE TO THE JTWC TRACK FORECAST. THERE IS ONLY MEDIUM
CONFIDENCE IN THE INTENSITY FORECAST GIVEN THE POSSIBILITY OF AN
EARLIER DISSIPATION. 

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