WDPS31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.6S 152.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 427 NM EAST-NORTHEAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTIVE BANDS WRAPPING INTO AN OBSCURED LOW-LEVEL CIRCULATION
CENTER. CIRRUS FILAMENTS LEAD INTO A STRONG POLEWARD AND EASTWARD
OUTFLOW CHANNEL ENHANCED BY THE JET TO THE SOUTH. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED ANIMATED EIR. THE INITIAL INTENSITY OF 55 KTS IS
ASSESSED WITH LOW CONFIDENCE BASED THE AGENCY AND OBJECTIVE FIXES
BELOW, BUT IS LESS CERTAIN DUE TO A 230800Z RCM-1 SYNTHETIC
APERTURE RADAR WIND SPEED PRODUCT INDICATING MAXIMUM WIND SPEEDS UP
TO 83KTS, WHICH IS CONSIDERABLY HIGH GIVEN THE STRUCTURE OF THE
SYSTEM.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A NEAR EQUATORIAL RIDGE TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   ABRF: T3.5 - 55 KTS
   CIMSS SATCON: 57 KTS AT 230846Z
   CIMSS ADT: 57 KTS AT 231130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE RATE OF INTENSIFICATION IS SLOWER
THAN REFLECTED IN THE PREVIOUS WARNING DUE TO HIGH VERTICAL WIND
SHEAR THAT IS INTRODUCED AFTER TAU 48 AND CONTINUES TO ERODE THE
CIRCULATION FOR THE REMAINDER OF THE FORECAST.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 18P WILL SLOWLY CURVE
FROM AN EASTWARD TRACK DURING THE FIRST 24 HOURS OF THE FORECAST
PERIOD TO A SOUTH-SOUTHEASTWARD TRACK BY THE END OF THE FORECAST
PERIOD UNDER THE STEERING INFLUENCE OF A NEAR EQUATORIAL RIDGE TO
THE NORTHEAST. THE SYSTEM IS EXPECTED TO INTENSIFY TO A PEAK OF
80KTS WITHIN THE FIRST 48 HOURS DUE TO LOW VERTICAL WIND SHEAR AND
CONTINUED STRONG POLEWARD OUTFLOW. AFTER TAU 48, VERTICAL WIND
SHEAR WILL INCREASE UNFAVORABLY TO 20-25KTS RESULTING IN WEAKENING
TO 60 KTS BY THE END OF THE FORECAST. DESPITE THE UNFAVORABLE
SHEAR, SEA SURFACE TEMPERATURES AND OUTFLOW WILL REMAIN SUPPORTIVE.


MODEL DISCUSSION: THE JTWC MULTI-MODEL CONSENSUS HAS A LARGE SPREAD
OF MODEL SOLUTIONS LEADING TO A CROSS-TRACK SPREAD OF 373NM BY THE
END OF THE FORECAST. THE SPREAD OF SOLUTIONS CAN BE ATTRIBUTED TO
DIFFERENT VARIATIONS OF HOW SHARPLY THE NEAR EQUATORIAL RIDGE
DRIVES THE SYSTEM AND WHETHER OR NOT THE RIDGE BREAKS DOWN. THE
INTENSITY GUIDANCE IS LARGELY SPREAD BETWEEN THE RAPID
INTENSIFICATION AIDS AND HAFS-A, HWRF, COAMPS-TC, AND GFS WHICH
DEPICT MINIMAL INTENSIFICATION IN THE NEAR-TERM FORECAST. WITHOUT
BITING OFF COMPLETELY ON THE SUDDEN DROP IN INTENSIFICATION
GUIDANCE, THE FORECAST INTENSITY WAS LOWERED BASED ON THE NEWLY
INDICATED SHEAR AFTER TAU 48.

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