WDPS31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.6S 155.8E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 391 NM NORTH-NORTHEAST OF BRISBANE,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 51 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) SHOWS A RATHER 
LARGE SYSTEM IN THE CORAL SEA WITH A RECENTLY OBSCURED RAGGED EYE
OVER THE CENTRAL DENSE OVERCAST WITH OVERSHOOTING COLD CLOUD TOPS 
HEIGHT REACHING -79 CELSIUS. THE INITIAL POSITION IS CENTERED WITH
A HIGH DEGREE OF CONFIDENCE BASED ON THE EIR LOOP EYE FEATURE THAT 
JUST CLOSED INTO A DIMPLE. THE INITIAL INTENSITY IS ALSO PLACED WITH 
THE SAME CONFIDENCE BASED ON AGENCY AND AUTOMATED DVORAK ESTIMATES
WEIGHTED ON THE HIGH END TO REFLECT A SUSTAINED 12-HR TIGHT WRAP AND
CONVECTIVE STRUCTURE. ANALYSIS INDICATES THAT VERTICAL WIND SHEAR
REACHED HIGH VALUES (20-25KTS), OFFSETTING THE WARM ALONG-TRACK SST, 
INFLUX OF MOISTURE, AND STRONG POLEWARD OUTFLOW (AS INDICATED BY LONG 
CIRRUS STREAKS STREAMING POLEWARD IN THE EIR LOOP). THE EFFECT OR 
KEY OUTCOME IS A MARGINAL ENVIRONMENT. TC ALFRED IS TRACKING ON THE
OUTER WEST RIM OF THE SUBTROPICAL RIDGE TO THE EAST AND IT IS ALSO
UNDER THE INFLUENCE OF THE STR TO THE WEST. THIS IS RESULTING IN 
THE SLOWER AND ZIG-ZAG STORM MOTION.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE ENE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 80 KTS AT 281958Z
   CIMSS ADT: 99 KTS AT 282330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC ALFRED WILL TRACK SOUTHWESTWARD,
SOUTHEASTWARD, THEN AFTER TAU 72, WESTWARD AS THE TWO COMPETING
STRS CONTINUE TO COMPETE RESULTING IN A MORE PRONOUNCED ZIG-ZAG
STORM MOTION. AS THE SYSTEM MOVES POLEWARD, THE ENVIRONMENT WILL
BECOME UNFAVORABLE MOSTLY DUE TO INCREASING VWS, RESULTING IN A
GRADUAL WEAKENING DOWN TO 65KTS BY TAU 96 AS THE TC BEELINES TOWARD
AUSTRALIA JUST NORTH OF BRISBANE.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT
WITH A SPREAD TO 123NM BY TAU 72, THEN WIDELY AND ERRATICALLY TO
445NM BY TAU 120. IN VIEW OF THESE PLUS THE UNCERTAINTIES BROUGHT
ON BY TWO COMPETING STEERING MECHANISMS, THERE IS ONLY MEDIUM
CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECASTS UP TO TAU 72,
THEN LOW CONFIDENCE AFTERWARD.

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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