WDXS31 PGTW 120300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 17S (ZELIA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.1S 118.6E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 317 NM NORTHEAST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
PERSISTENT CONVECTION BUILDING OVER THE LOW-LEVEL CIRCULATION
CENTER. VERY HOT TOWERS CAN BE IDENTIFIED AS WARM SPOTS ON THE
ANIMATED EIR, INDICATIVE OF THE SIGNIFICANT INTENSIFICATION THAT
HAS OCCURRED OVER THE LAST SIX HOURS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT
BETWEEN TWO SUBTROPICAL RIDGES (STR) TO THE EAST AND WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 53 KTS AT 110040Z
   CIMSS AIDT: 41 KTS AT 110040Z
   CIMSS D-PRINT: 61 KTS AT 110040Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE PEAK INTENSITY IS HIGHER THAN THE
PREVIOUS FORECAST DUE TO A HIGHER RATE OF INTENSIFICATION.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 17S IS FORECAST TO
REMAIN QUASI-STATIONARY (QS) FOR THE FIRST 48 HOURS OF THE
FORECAST, RESULTING IN AN IRREGULAR MOTION OVER WARM SEA SURFACE
TEMPERATURES BETWEEN 29-30C. THE UPPER-LEVEL ENVIRONMENT IS HIGHLY
FAVORABLE FOR DEVELOPMENT RESULTING PROVIDING A POLEWARD OUTFLOW
CHANNEL INTO A JET MAXIMUM. VERTICAL WIND SHEAR WILL DECREASE
FAVORABLY, CONTRIBUTING TO RAPID INTENSIFICATION TO A PEAK OF
105KTS BY TAU 48. AFTER THE SYSTEM MAKES LANDFALL, THE SYSTEM WILL
BEGIN TO SHALLOW AND TRACK SOUTHWARD QUICKLY WHILE DRIVEN BY MID-
AND LOW-LEVEL FLOW. THE TOPOGRAPHIC INTERACTION OVER THE DRY LAND
WILL LEAD TO DISSIPATION OVER LAND BY TAU 120. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE HAS A SIGNIFICANT
SPREAD OF POTENTIAL TRACKS IN THE NEAR-TERM DUE TO THE
QUASI-STATIONARY NATURE OF THE SYSTEM. THE ENSEMBLES GUIDANCE LEADS
TO FURTHER LOW CONFIDENCE DUE TO A LARGE POTENTIAL SPREAD
REPRESENTED BY BOTH THE ECMWF AND GFS ENSEMBLES. THE AMOUNT OF TIME
THAT THE SYSTEM REMAINS OVER WATER WILL GREATLY INFLUENCE THE RATE
OF INTENSIFICATION. IF THE SYSTEM TRACKS FARTHER WEST, AS
REPRESENTED IN GFS, THE SYSTEM MAY EXCEED THE MAXIMUM INTENSITY
REFLECTED IN THE FORECAST.

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