WDPS31 PGTW 060300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.3S 155.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 145 NM EAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER AS TROPICAL CYCLONE (TC) 18P
SLOWLY MEANDERS TOWARDS THE EASTERN COAST OF AUSTRALIA. THE TRACK
MOTION OVER THE LAST 6 HOURS HAS BEEN IRREGULAR DUE TO WEAK
STEERING FLOW AS THE SYSTEM HAS SHALLOWED OVER THE LAST 12 HOURS.
DEEP CONVECTION IS DISPLACED TO THE SOUTH DUE TO HIGH VERTICAL WIND
SHEAR FROM THE NORTHEAST. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED EIR. THE INITIAL
INTENSITY OF 50 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON A
052206Z METOP-B ASCAT WIND SPEED IMAGE REVEALING 50KT WINDS TO THE
SOUTH OF THE CIRCULATION.

INITIAL WIND RADII BASIS: 052206Z METOP-B SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: A WEAK STEERING ENVIRONMENT BETWEEN A
RIDGE OVER AUSTRALIA AND A NEAR EQUATORIAL RIDGE TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   ABRF: T2.5 - 35 KTS
   CIMSS SATCON: 48 KTS AT 052034Z
   CIMSS ADT: 30 KTS AT 052030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 IS FORECAST TO TRACK
WESTWARD FOR THE REMAINDER OF THE FORECAST PERIOD. THE SYSTEM WILL
MAKE LANDFALL IN THE VICINITY OF BRISBANE BETWEEN TAU 36-48. THE
SLOW AND IRREGULAR TRACK OF THE SYSTEM WILL CONTINUE FOR THE
REMAINDER OF THE FORECAST PERIOD, RESULTING IN A UPWELLING IN
ALREADY COOL WATERS. WEAKENING WILL CONTINUE DUE TO THE COOL SEA
SURFACE TEMPERATURES AND STRONG VERTICAL WIND SHEAR INTRODUCED BY
AN APPROACHING UPPER-LEVEL TROUGH. THE INTENSITY AT TAU 36, JUST
PRIOR TO LANDFALL, IS ANTICIPATED TO BE 40KTS. FURTHER WEAKENING TO
DISSIPATION IS EXPECTED BY TAU 48.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL TRACK WESTWARD FOR THE REMAINDER OF THE
FORECAST PERIOD WITH A CROSS-TRACK SPREAD OF 46 NM BY TAU 48. SOME
MODELS, SUCH AS NAVGEM AND GFS, INDICATE A MORE NORTHWESTWARD TRACK
THAN OTHERS DUE TO AN EXTENSION OF THE AUSTRALIAN RIDGE ORIENTED
FROM THE NORTHWEST TO THE SOUTHEAST THAT IS NOT AS STRONG ON OTHER
MODEL GUIDANCE. THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT
WEAKENING WILL OCCUR FOR THE REMAINDER OF THE FORECAST DUE TO COOL
SEAS SURFACE TEMPERATURES, HIGH VERTICAL WIND SHEAR, AND
TOPOGRAPHIC INTERACTION.

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