WDPS31 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.5S 153.7E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 38 NM EAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 18P (ALFRED) ON A WEST-NORTHWESTWARD TRACK, AS IT
APPROACHES NORTH STRADBROKE ISLAND AND MORETON ISLAND. LOW-LEVEL
CIRCULATION REMAINS RELATIVE SYMMETRICAL, WITH MAJORITY OF THE DEEP
CONVECTION THROUGHOUT THE SOUTHERN SEMICIRCLE OF THE SYSTEM. TC 18P
BENEFITTED FROM RECENT INJECTION OF WARMER (26-27 C) WATER
ORIGINATING WITHIN THE EAST AUSTRALIAN CURRENT, AS WELL AS SLIGHTLY
REDUCED (25-30 KTS) VERTICAL WIND SHEAR (VWS). THEREFORE, OVER THE
LAST 12 HOURS, THE SYSTEM WAS ABLE TO MAINTAIN 40-45 KTS INTENSITY,
WHICH IS CURRENTLY ASSESSED WITH MEDIUM CONFIDENCE BASED ON AGENCY
DVORAK FIXES, OBJECTIVE ESTIMATES LISTED BELOW, AS WELL AS SYNOPTIC
OBSERVATIONS FROM MAIN BEACH, GOLD COAST, AUSTRALIA, INDICATING 41
KTS, 10-MINUTE AVERAGED WIND. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE EIR SATELLITE LOOP AND THE RADAR FIXES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: 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
   ABRF: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 070754Z
   CIMSS ADT: 39 KTS AT 071130Z
   CIMSS AIDT: 39 KTS AT 071130Z
   CIMSS D-MINT: 38 KTS AT 070755Z
   CIMSS D-PRINT: 37 KTS AT 071130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: UPPER-LEVEL TROUGH, LAND INTERACTION AND DRY AIR
ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 18P IS FORECAST TO CROSS THE MORETON BAY
ISLANDS AND MAKE LANDFALL JUST NORTH OF BRISBANE WITHIN THE NEXT 12
HOURS. THE STR TO THE SOUTH IS DOMINATING THE STEERING PATTERN AT THE
MOMENT, AS INDICATED BY THE WEST-NORTHWESTWARD TURN OCCURRING
WITHIN THE LAST 6-12 HOURS. SLIGHT INCREASE IN CONVECTIVE ACTIVITY IS 
HIGHLY POSSIBLE OVER THE NEXT 6 HOURS, AS TC ALFRED IS TRANSITING 
THROUGH A PATCH OF WARMER WATER. AFTERWARDS, THE SYSTEM IS FORECAST TO 
BEGIN RAPIDLY WEAKENING DUE TO LAND INTERACTION, INCREASING VWS, AS 
WELL AS A PASSING UPPER-LEVEL TROUGH. AS THE SYSTEM MAKES LANDFALL IT 
IS FORECAST TO BEGIN ROUNDING THE NORTHERN PERIPHERY OF THE RIDGE AND 
TURN SOUTHWESTWARD, WHILE FULLY DISSIPATING BY TAU 24. 

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH ALL MODELS CLOSELY GROUPED, LEADING TO JTWC TRACK
GUIDANCE TO BE ASSESSED WITH HIGH CONFIDENCE AND IN CLOSE PROXIMITY
TO THE MULTI-MODEL CONSENSUS. THE ONLY MINOR OUTLIER IS NAVGEM,
WHICH IS PREDICTING A TRACK FASTER THAN ALL OTHER MODELS. HIGH
TRACK FORECAST CONFIDENCE IS ALSO REFLECTED BY THE 13 NM
CROSS-TRACK SPREAD AT LANDFALL. JTWC INTENSITY GUIDANCE IS ALSO
ASSESSED WITH HIGH CONFIDENCE, AS ALL AVAILABLE MODELS INDICATE
SIMILAR IMPACT OF CHANGING ENVIRONMENT, LEADING TO FULL DISSIPATION
BY THE END OF THE FORECAST PERIOD.

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