WDPS31 PGTW 031500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.7S 158.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 283 NM EAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION (LLCC) OF TROPICAL CYCLONE (TC)
ALFRED (18P) WITH MAJORITY OF THE DEEP CONVECTION CONTAINED WITHIN THE 
SOUTHERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS REVEALS STRONG POLEWARD
OUTFLOW, COOLING (25-26 C) SEA SURFACE TEMPERATURES, STRONG (35-40
KTS) DEEP-LAYER VERTICAL WIND SHEAR (VWS) AND SIGNIFICANT AMOUNT OF
DRY AIR ENTRAINING INTO THE CORE OF THE SYSTEM FROM THE NORTHWEST.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
LOW-LEVEL CIRCULATION CENTER (LLCC) PRESENT IN THE EIR LOOP, AS
WELL AS IN THE 031133Z METOP-B ASCAT DATA. THE INITIAL INTENSITY
OF 50 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED ASCAT DATA.

INITIAL WIND RADII BASIS: 031133Z METOP-B ASCAT DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   ABRF: T2.5 - 35 KTS
   CIMSS SATCON: 44 KTS AT 030835Z
   CIMSS ADT: 30 KTS AT 031140Z
   CIMSS AIDT: 38 KTS AT 031140Z
   CIMSS D-MINT: 42 KTS AT 030759Z
   CIMSS D-PRINT: 32 KTS AT 031300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 35-40 KTS
   SST: 25-26 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 TRACK SOUTHEASTWARD FOR
THE NEXT 12 HOURS, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR TO
THE EAST. AFTERWARDS, THE STEERING PATTERN WILL SHIFT, AS THE STR
TO THE EAST MOVES NORTH, WHILE AN EXTENSION OF ANOTHER STR
ORIGINATING OVER AUSTRALIA ASSUMES THE PRIMARY STEERING. BY TAU 24,
THE STR TO THE SOUTH WILL CAUSE TC ALFRED TO SHARPLY TURN WESTWARD.
AS THE SYSTEM STARTS TRACKING TOWARDS THE COAST OF AUSTRALIA, THE
STR WILL REORIENT FROM NORTHWEST-SOUTHEAST, TO A
SOUTHWEST-NORTHEAST AXIS. THIS CHANGE IN THE STEERING WILL LEAD TO
TC 18P TAKING A SLIGHT WEST-NORTHWESTWARD TURN, FOLLOWED BY A
WEST-SOUTHWESTWARD TURN JUST BEFORE LANDFALL AND EVENTUAL
DISSIPATION. IN REGARD TO THE INTENSITY FORECAST, TC 18P IS
EXPECTED TO SLIGHTLY INTENSIFY, WHILE MAKING THE SHARP WESTWARD
TURN, UTILIZING THE INJECTION OF MOIST AIR FROM THE SOUTH AND
SOUTHEAST. AFTERWARDS THE SYSTEM IS EXPECTED TO BEGIN WEAKENING AS
IT TRANSITS TOWARDS AUSTRALIA AND THE ENVIRONMENTAL CONDITIONS
BECOME LESS FAVORABLE, WITH COOLING SST, INCREASING WIND SHEAR,
INCREASING DRY AIR AND REDUCED OUTFLOW ALOFT. LANDFALL IS EXPECTED
SHORTLY AFTER TAU 72, JUST NORTH OF BRISBANE.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT WITH ALL MODELS INDICATING STEERING MECHANISM SHIFT AND A
SHARP WESTWARD TURN, WITH JUST 40 NM CROSS-TRACK SPREAD, INCREASING
TO JUST 60 NM BY LANDFALL. UNCERTAINTY IS INCREASED HOWEVER DUE TO
THE ALONG-TRACK SPREAD AS HIGH AS 165 NM BY TAU 72. THE FASTEST
MODEL IS CURRENTLY NAVGEM, WHILE THE SLOWEST ARE UKMET ENSEMBLE AND
ECMWF. REMAINING MODEL TRACKERS ARE IN RELATIVELY TIGHT AGREEMENT.
JTWC TRACK FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE AND IS LAID
CLOSE, BUT A LITTLE SLOWER THAN THE MULTI-MODEL CONSENSUS,
OFFSETTING THE FASTEST NAVGEM. NUMERICAL MODEL INTENSITY GUIDANCE
IS ALSO IN FAIR AGREEMENT, WITH ALL MODELS INDICATING THE INTENSITY
TO OSCILLATE BETWEEN 50 AND 60 KTS UNTIL TAU 72. AFTERWARD, LAND 
INTERACTION IS INDICATED BY ALL MODELS PREDICTING RAPID WEAKENING
AND DISSIPATION BY TAU 96.

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