WDPS31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.7S 155.4E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 551 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS IMPROVING
CONVECTIVE ORGANIZATION AROUND A PRECURSOR EYE FEATURE. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON 262213Z GMI 37 GHZ
IMAGERY SHOWING A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER. THE
INITIAL INTENSITY OF 95 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON A CONSENSUS OF AVAILABLE SUBJECTIVE DVORAK AND AUTOMATED
INTENSITY FIX DATA.

INITIAL WIND RADII BASIS: SAR DATA (261907Z RCM-1 PASS) AND SMOS
DATA (261955Z PASS)

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   ABRF: T4.5 - 77 KTS
   CIMSS ADT: 72 KTS AT 262320Z
   CIMSS AIDT: 79 KTS AT 262320Z
   CIMSS D-PRINT: 84 KTS AT 262340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORWARD TRACK SPEEDS ARE
SIGNIFICANTLY FASTER IN THE EXTENDED PERIOD RELATIVE TO THE
PREVIOUS FORECAST BASED ON EXPECTATIONS OF A SMOOTHER AND STRONGER
POLEWARD STEERING FLOW.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 18P WILL CONTINUE
TRACKING GENERALLY POLEWARD THROUGH THE ENTIRETY OF THE FORECAST
PERIOD UNDER THE ONGOING STEERING INFLUENCE OF THE STR TO THE EAST.
A SLIGHT WESTWARD JOG IS POSSIBLE AFTER TAU 36 AS A SUBTROPICAL
RIDGE BUILDS TO THE SOUTHWEST AND NUDGES THE SYSTEM, BUT THE
INFLUENCE OF THIS RIDGING WILL LIKELY BE MUTED. WHILE THE CURRENT
FORECAST CALLS FOR A GENERALLY STEADY INTENSITY TREND OVER THE NEXT
12 TO 24 HOURS, ADDITIONAL INTENSIFICATION IS POSSIBLE AS VERTICAL
WIND SHEAR REMAINS LOW AND POLEWARD OUTFLOW ROBUST. HOWEVER,
VERTICAL WIND SHEAR IS EXPECTED TO INCREASE AS UPPER-LEVEL FLOW
AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE TO THE EAST IMPACTS
THE SYSTEM, EVENTUALLY RESULTING IN A SLOW WEAKENING TREND. BY TAU
120, THE SYSTEM IS EXPECTED TO PASS OVER COOLER WATER (BELOW 26C),
BUT THE INTENSITY WILL HOLD STEADY OR DROP VERY SLOWLY AT THAT
POINT DUE TO AN INJECTION OF BAROCLINIC SUPPORT. BEYOND THE
FORECAST PERIOD, SUBTROPICAL TRANSITION APPEARS LIKELY.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT REGARDING
THE OVERALL FORECAST SCENARIO AND DERIVED TRACKS ARE FAIRLY TIGHTLY
PACKED THROUGH TAU 72, PROVIDING HIGH CONFIDENCE TO THE EARLY
PORTION OF THE FORECAST. SPREAD INCREASES THEREAFTER AS
DETERMINISTIC CONSENSUS MODELS AND INDIVIDUAL MEMBERS OF GLOBAL
ENSEMBLES (GEFS, EC-EPS) INDICATE UNCERTAINTY ASSOCIATED WITH THE
INFLUENCE OF A BUILDING RIDGE TO THE SOUTHWEST AFTER TAU 36.
SOLUTIONS THAT JOG THE SYSTEM FARTHER WESTWARD ARE ALSO SLOWER TO
TURN AND ACCELERATE POLEWARD. TRENDS IN THE FORECAST GUIDANCE
SUGGEST THAT ANY WESTWARD JOG AFTER TAU 36 WILL LIKELY BE SMALL AND
SHORT LIVED, WHICH THE SUBTROPICAL RIDGE TO THE EAST DOMINATING
STEERING. THE CURRENT TRACK FORECAST LIES SLIGHTLY TO THE EAST AND
A BIT FASTER THAN THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE
IN THE EXTENDED RANGE. NEAR-TERM INTENSITY CHANGE IS A BIT
UNCERTAIN, WITH HAFS REFLECTING A BUMP TO APPROXIMATELY 105 KTS BUT
ALL OTHER SOLUTIONS HOLDING STEADY OR WEAKENING SLOWLY. THE TREND
TOWARD SLOW WEAKENING IS SHARED ACROSS MODEL SOLUTIONS AFTER TAU
36. OVERALL, THERE IS MEDIUM CONFIDENCE IN THE INTENSITY FORECAST. 

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