WDPS31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.4S 155.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 286 NM NORTH-NORTHEAST OF BRISBANE,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 19P (ALFRED) WITH A WELL-DEFINED, COMPLETELY EXPOSED
LOW-LEVEL CIRCULATION CENTER. THE DEEP CONVECTION THAT WAS OVER THE
CENTER OF THE SYSTEM 12 HOURS AGO HAS NOW DISSIPATED AND IS NOW
CONFINED TO THE SOUTHERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS
INDICATES THAT 18P IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY
STRONG POLEWARD OUTFLOW ALOFT, MODERATE (15-20 KTS) VERTICAL WIND
SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES HEAVILY OFFSET
BY EXTENSIVE DRY AIR ENTRAINMENT ALONG THE ENTIRE NORTHERN HALF OF
THE VORTEX. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE EXPOSED LLCC IN THE ANIMATED MSI. THE INITIAL
INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
HIGHER SIDE OF THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES
LISTED BELOW. THE LACK OF CONVECTION HAS CAUSED MANY INTENSITY
ESTIMATES TO RAPIDLY DECREASE. SURFACE OBSERVATIONS FROM CATO
ISLAND HAVE RECENTLY DROPPED IN INTENSITY AS THE BROAD CORE OF
WEAKER WINDS PASSED NEARLY DIRECTLY OVER THE ISLAND. HOWEVER,
AROUND 6 HOURS AGO, WINDS WERE REPORTED TO BE NEAR 48 KTS (AFTER
CONVERSION TO 1-MINUTE AVERAGE) FROM THE EAST. A PARTIAL 012237Z
METOP-C ASCAT UHR IMAGE REVEALS 45-49 KNOT WINDS WITHIN THE WESTERN
PERIPHERY WHILE MISSING THE EASTERN PORTION OF THE SYSTEM.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   ABRF: T3.0 - 45 KTS
   CIMSS SATCON: 52 KTS AT 020010Z
   CIMSS ADT: 32 KTS AT 012330Z
   CIMSS AIDT: 42 KTS AT 012330Z
   CIMSS DMINT: 44 KTS AT 012138Z
   CIMSS MW SOUNDERS: 54 KTS AT 012237Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: EXTENSIVE DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 TRACK
SOUTH-SOUTHEASTWARD ALONG THE WESTERN PERIPHERY OF THE STR THROUGH
TAU 48. AFTER TAU 48, THE RIDGE REORIENTS DUE TO A SHARP LONGWAVE
TROUGH BREAKING DOWN THE RIDGE. THE BREAK IN THE RIDGE ALLOWS FOR
RIDGING EXTENDING FROM SOUTHERN AUSTRALIA TO BUILD SOUTH OF THE
SYSTEM. THIS WILL THEN DRIVE 18P WESTWARD, TOWARD THE EASTERN COAST
OF AUSTRALIA THROUGH THE REMAINDER OF THE FORECAST PERIOD.
LANDFALL IS CURRENTLY FORECAST TO OCCUR ABOUT 40 NM NORTH OF
BRISBANE AROUND TAU 108, BUT IT IS UNCERTAIN AT THIS TIME.
REGARDING INTENSITY, 18P IS FORECAST TO MAINTAIN INTENSITY THROUGH
TAU 48 AS STRONG POLEWARD OUTFLOW AND WARMISH SEA SURFACE
TEMPERATURES FIGHT AGAINST DRY AIR AND INCREASING VERTICAL WIND
SHEAR. AFTER TAU 48, THE POLEWARD OUTFLOW CHANNEL WILL BEGIN TO
DIMINISH, WHICH WILL CAUSE 18P TO WEAKEN AS IT APPROACHES THE
COAST. AFTER LANDFALL, 18P WILL QUICKLY WEAKEN DUE TO TERRAIN
INTERACTION AND IS FORECAST TO DISSIPATE BY TAU 120, NORTHWEST OF
BRISBANE.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN SLIGHTLY POOR
AGREEMENT. THE GFS AND ITS ENSEMBLE MEAN BOTH ARE OUTLIERS FROM THE
REMAINDER OF CONSENSUS. THEY BOTH DEPICT A MUCH SLOWER TRACK SPEED
THROUGH TAU 48. THE RESULT IS THAT THEY HAVE THE WESTWARD TURN
BEGINNING MUCH FURTHER NORTH. ALL MODELS HAVE THE WESTWARD TURN
AFTER TAU 48, BUT THE TIME AND LOCATION OF LANDFALL ARE UNCERTAIN
DUE TO THE DISCREPANCY IN TRACK SPEEDS LEADING UP TO TAU 48.
LANDFALL LOCATIONS CURRENTLY EXTEND FROM THE RAINBOW BEACH AREA TO
JUST SOUTH OF BRISBANE. THE JTWC TRACK FORECAST IS PLACED WITH
OVERALL LOW CONFIDENCE DUE TO THE LARGE TRACK SPREAD THROUGHOUT THE
ENTIRETY OF THE FORECAST PERIOD. INTENSITY GUIDANCE IS IN
SURPRISINGLY GOOD AGREEMENT WITH ALL MODELS SUGGESTING A STEADY
INTENSITY THROUGH TAU 48 WITH WEAKENING THEREAFTER. THE JTWC
INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE DUE TO THE
UNCERTAINTIES ASSOCIATED WITH THE TIMING AND LOCATION OF LANDFALL. 

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