WDPS31 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.6S 154.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 80 NM EAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS WEAK
CONVECTIVE BANDING WRAPPING INTO THE PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC). THE SYSTEM PREVIOUSLY HAD STRONGER
SUBTROPICAL CHARACTERISTICS OF COOL SEA SURFACE TEMPERATURES, BUT
HAS NOW RE-INTRODUCED INSTABILITY FUELED BY WARM WATERS OF THE
COASTAL CURRENT ALONG THE GOLD COAST OF AUSTRALIA. WATER VAPOR
IMAGERY HIGHLIGHTS THE RE-INTRODUCTION OF WARM MOISTURE AND STRONG
POLEWARD OUTFLOW ALOFT. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED MSI. THE LOW-LEVEL
CLOUD BANDING WRAPPING INTO THE CIRCULATION CENTER IS EVIDENT ON
RADAR IMAGERY AND ALSO ASSISTED POSITIONING. THE INITIAL INTENSITY
OF 45 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON A 062238Z
METOP-C ASCAT IMAGE REVEALING 35-40KT WINDS TO THE SOUTHEAST AND
EARLIER 061910Z RCM-2 SYNTHETIC APERTURE RADAR WIND SPEED DATA
INDICATING WIND SPEEDS ABOVE 50KTS. SYNOPTIC OBSERVATIONS AT CAPE
BYRON SOUTHEAST OF THE SYSTEM INDICATE 37KTS OF WIND WITH A
10-MINUTE AVERAGE.

INITIAL WIND RADII BASIS: 061910Z RCM-2 SYNTHETIC APERTURE RADAR
WIND SPEED DATA

CURRENT STEERING MECHANISM: A WEAK STEERING ENVIRONMENT BETWEEN A
SUBTROPICAL RIDGE (STR) TO THE SOUTHWEST AND A NEAR EQUATORIAL
RIDGE (NER) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 061926Z
   CIMSS ADT: 35 KTS AT 062030Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 18P WILL SLOWLY TRACK
WEST-NORTHWESTWARD FOR THE REMAINDER OF THE FORECAST PERIOD WITH
LIKELY IRREGULAR MOTION GUIDED BY THE CONTINUING COMPETING STEERING
ENVIRONMENT. THE SLIGHT CURVATURE TO THE WEST-NORTHWEST WILL BE
DRIVEN BY THE BUILDING SUBTROPICAL RIDGE TO THE SOUTH. THE SYSTEM
INTENSITY WILL WEAKEN AS THE UPPER-LEVEL ENVIRONMENT IS NO LONGER
DIVERGENT DUE TO AN UPSTREAM UPPER-LEVEL TROUGH AND HIGH VERTICAL
WIND SHEAR THAT WILL CONTINUE FOR THE REST OF THE FORECAST. AFTER
LANDFALL BETWEEN TAU 12-24, TOPOGRAPHIC INTERACTION, LACK OF A
MOISTURE SOURCE, AND DRY AIR WILL LEAD THE SYSTEM TO DISSIPATION BY
TAU 36. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN STRONG
AGREEMENT THAT THE SYSTEM WILL TRACK WESTWARD TO WEST-NORTHWESTWARD
FOR THE NEXT 36 HOURS AS THE RIDGE TO THE SOUTHWEST BUILDS. IT IS
NOTABLE THAT DESPITE THE MODEL GUIDANCE, TC 18P HAS HAD AND WILL
CONTINUE TO HAVE A COMPETING STEERING ENVIRONMENT. THE INTENSITY
GUIDANCE IS ALSO IN GOOD AGREEMENT THAT THE TROPICAL CYCLONE WILL
DISSIPATE UNDER UNFAVORABLE CONDITIONS WITHIN THE NEXT 36 HOURS.

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