WDXS31 PGTW 230300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (NEVILLE) WARNING 
NR 039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3S 96.5E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 420 NM SOUTH OF COCOS ISLANDS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT,
NEAR-SYMMETRICAL SYSTEM WITH TIGHTLY WRAPPED FEEDER BANDS AND A
RAGGED 18-NM EYE. THE MSI LOOP ALSO SHOWS LOW LEVEL COLD AIR
STRATOCUMULUS CLOUD LINES INTRUDING INTO THE CENTER FROM THE
SOUTHWESTERN TO NORTHWESTERN PERIPHERIES. TRANSVERSE BANDS ARE ALSO
EVIDENT ON THE CIRRUS CLOUDS SPIRALING OUTWARD FROM THE CORE. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE
FEATURE. THE INITIAL INTENSITY OF 85KTS IS ALSO PLACED WITH HIGH
CONFIDENCE BASED ON OVERALL ASSESSMENT OF AGENCY AND AUTOMATED
DVORAK ESTIMATES THAT ARE SLOWLY TRENDING DOWN, AND REFLECTS THE
SLIGHT 12-HR DEGRADATION. ANALYSIS INDICATES THE ENVIRONMENT
REMAINS MARGINALLY UNFAVORABLE WITH THE MODERATE POLEWARD OUTFLOW
OFFSET BY COLD AIR INTRUSION, COOLING SST, AND INCREASING VWS.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE SOUTH.


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   APRF: T5.0 - 90 KTS
   CIMSS SATCON: 83 KTS AT 222130Z
   CIMSS ADT: 97 KTS AT 222330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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: TC NEVILLE WILL CONTINUE ON ITS CURRENT
WEST-SOUTHWESTWARD TRACK UNDER THE STEERING INFLUENCE OF THE STR TO
THE SOUTH. AFTER TAU 48, A DEEP MID-LATITUDE TROUGH APPROACHING
FROM THE WEST WILL WEAKEN THE STR AND ALLOW THE SYSTEM TO TRACK
MORE SOUTHWARD. THE ENVIRONMENT WILL BECOME MORE UNFAVORABLE WITH
THE PERSISTENT AND INCREASING EFFECTS OF COLD AIR ADVECTION,
COOLING SST, AND INCREASING VWS. THIS WILL PROMOTE A FASTER THAN
NORMAL DECAY, LEADING TO DISSIPATION BY TAU 72.   

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH A
GRADUAL AND EVEN SPREAD TO 182NM BY TAU 72, LENDING HIGH CONFIDENCE
TO THE JTWC TRACK FORECAST. 

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