WDPS31 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.8S 157.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 250 NM EAST-NORTHEAST OF BRISBANE,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 18P (ALFRED) WITH AN EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) AND CONVECTION CONFINED TO THE SOUTHEASTERN QUADRANT. STRONG
NORTHWESTERLY SHEAR CAN BE SEEN ACTING ON THE SYSTEM, CAUSING THE
CONVECTION TO STREAM OFF TOWARD THE SOUTHEAST. ENVIRONMENTAL
ANALYSIS INDICATES THAT 18P IS IN A MARGINAL ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, HIGH (25-30 KTS)
VERTICAL WIND SHEAR, EXTENSIVE DRY AIR ENTRAINMENT, AND WARM (26-27
C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE ANIMATED MSI. THE
INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW. ADDITIONALLY, A 022217Z METOP-C ASCAT UHR IMAGE REVEALED A
45-47 KNOT WIND FIELD WITH A SMALL PATCH OF 50-55 KTS WITHIN THE
SOUTHERN SEMICIRCLE.

INITIAL WIND RADII BASIS: 022217Z SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   ABRF: T3.0 - 45 KTS
   CIMSS SATCON: 51 KTS AT 022011Z
   CIMSS ADT: 43 KTS AT 022330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: EXTENSIVE DRY AIR ENTRAINMENT

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: TC 18P IS FORECAST TO CONTINUE TRACKING
SOUTHEASTWARD, ALONG THE WESTERN PERIPHERY OF THE STR THROUGH TAU
24. NEAR TAU 24, AN INCOMING LONGWAVE TROUGH WILL BREAK DOWN THE
RIDGE, ALLOWING FOR RIDGING EXTENDING FROM SOUTHERN AUSTRALIA TO
BUILD TO THE SOUTH OF THE SYSTEM. THIS WILL CAUSE 18P TO TURN
SHARPLY WESTWARD AND HEAD TOWARD THE EASTERN COAST OF AUSTRALIA.
LANDFALL IS CURRENTLY FORECAST TO OCCUR NEAR TAU 84, ABOUT 45 NM
NORTH OF BRISBANE, THOUGH THE EXACT TIMING AND LOCATION IS STILL
UNCERTAIN. REGARDING INTENSITY, 18P IS FORECAST TO INTENSIFY
MARGINALLY OVER THE NEXT 12 HOURS DUE TO THE STRONG POLEWARD OUTFLOW
CHANNEL. HOWEVER, AROUND AFTER TAU 24, SEA SURFACE TEMPERATURE
WILL DROP BELOW 26 C AND VERTICAL WIND SHEAR WILL CONTINUE TO RISE,
CAUSING 18P TO BEGIN WEAKENING AS IT APPROACHES THE COAST.
ADDITIONALLY, NEAR TAU 72, THE POLEWARD OUTFLOW CHANNEL WILL
DIMINISH DUE TO THE JET MAX PROPAGATING EASTWARD, AWAY FROM THE
VORTEX. AS A RESULT, THE SYSTEM IS FORECAST TO BE AROUND 45 KTS AS
IT MAKES LANDFALL. AFTER LANDFALL, TERRAIN INTERACTION WILL CAUSE
18P TO QUICKLY DISSIPATE AS IT TRACKS FURTHER WESTWARD.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN SLIGHTLY WORSE
AGREEMENT THAN DURING THE PREVIOUS FORECAST. CROSS-TRACK SPREAD 
REMAINS RELATIVELY TIGHT WHILE ALONG-TRACK SPREAD HAS NOTABLY 
INCREASED. GFS AND ITS ENSEMBLE MEAN HAVE A MUCH FASTER TRACK SPEED 
THAN THE REMAINDER OF GUIDANCE, WITH THE VORTEX ALREADY MAKING 
LANDFALL AT TAU 72 AND RACING QUICKLY WESTWARD AFTER TAU 72. ON THE 
OTHER HAND, ECMWF AND ITS ENSEMBLE MEAN HAVE THE SYSTEM STILL OFF THE 
COAST AT TAU 96. THE JTWC TRACK FORECAST IS PLACED SLOWER THAN 
CONSENSUS, A BIT CLOSER TO THE ECMWF SOLUTIONS WITH MEDIUM CONFIDENCE 
THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IS IN 
BETTER AGREEMENT, WITH ALL MODELS SUGGESTING SLIGHT INTENSIFICATION 
THOUGH TAU 12 WITH GRADUAL WEAKENING AFTERWARDS. THE JTWC INTENSITY 
FORECAST IS PLACED CLOSE TO CONSENSUS WITH OVERALL MEDIUM CONFIDENCE 
DUE TO THE UNCERTAINTIES ASSOCIATED WITH THE TRACK GUIDANCE.

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