WDPS31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.8S 155.7E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 569 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COLLAPSING EYE STRUCTURE AS TROPICAL CYCLONE (TC) 18P TRACKS
SOUTHWARD AT A SLOW MOTION. THE DEGRADING STRUCTURE IS RELATED TO
THE SIGNIFICANT UPWELLING OF COOL WATER. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON A 2711140Z METOP-B AMSU-B 89V
MICROWAVE IMAGE DEPICTING A BROKEN MICROWAVE EYE FEATURE. THE
INITIAL INTENSITY OF 115 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT
BETWEEN A DEEP-LAYER RIDGE TO THE EAST AND WEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   CIMSS SATCON: 81 KTS AT 271115Z
   CIMSS ADT: 115 KTS AT 271400Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 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 18P WILL REMAIN IN A COMPETING STEERING
ENVIRONMENT FOR THE FIRST 48 HOURS OF THE FORECAST PERIOD. AS A
RESULT, THE TRACK MOTION WILL BE SLOW MOVING AND NEARLY
QUASI-STATIONARY AT TIMES. AFTER TAU 48, THE TRACK SPEED WILL
INCREASE AS THE RIDGE TO THE EAST BECOMES THE PRIMARY STEERING
INFLUENCE, CAUSING THE SYSTEM TO CURVE SOUTHEASTWARD. TC 18P WILL
WEAKEN CONTINUALLY THROUGH THE END OF THE FORECAST DUE TO DRY AIR
ENTRAINMENT INTRODUCED BY HIGH VERTICAL WINDSHEAR FROM THE WEST AND
UPWELLING OF COOL SEA SURFACE TEMPERATURES. THE SYSTEM WILL WEAKEN
TO 65KTS BY THE END OF THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE HOLDS SOME
UNCERTAINTY DUE TO INTERPRETATIONS OF HOW STRONGLY THE RIDGES TO
THE EAST AND WEST DRIVE THE STORM. SOME MODELS DEPICT A FARTHER
WESTWARD TRACK, LIKE ECMWF, WHILE OTHERS MOVE FARTHER EAST, LIKE
NAVGEM. THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM
WILL WIND DOWN IN AN UNFAVORABLE ENVIRONMENT WITH MINIMAL SPREAD.

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