WDPS31 PGTW 040300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING 
NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.3S 159.0E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 320 NM EAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TC 18P
(ALFRED) WITH A FULLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC),
WITH ALL ASSOCIATED CONVECTION DISLOCATED TO THE SOUTHERN
SEMICIRCLE, INDICATIVE OF THE CYCLONE GAINING SUBTROPICAL CYCLONE
CHARACTERISTICS. STRONG VERTICAL WIND SHEAR (VWS) AND DRY-AIR
ENTRAINMENT HAS REMAINED EVIDENT THROUGHOUT THE NORTHERN HALF OF
THE SYSTEM, EXPOSING LOW-LEVEL CURVED AND FRAGMENTED CONVECTIVE
CLOUD LINES WRAPPING INTO THE LLCC. ENVIRONMENTAL ANALYSIS REVEALS
A STRONG UPPER-LEVEL POLEWARD OUTFLOW CHANNEL WITH ASSOCIATED
TRANSVERSE BANDING ALONG THE POLEWARD EDGE, COOLER SEA SURFACE
TEMPERATURES OF 25-26 C AND SUSTAINED STRONG VWS OF NEAR 50 KTS.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A
032243Z METOP-B ASCAT UHR PASS. THE INITIAL INTENSITY IS ASSESSED
WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED METOP-B ASCAT
DATA.

INITIAL WIND RADII BASIS: 032243Z METOP-B ASCAT UHR DATA

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) TO THE
NORTHEAST AND A SUBTROPICAL RIDGE (STR) TO THE WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   ABRF: T1.5 - 25 KTS
   CIMSS SATCON: 41 KTS AT 032230Z
   CIMSS ADT: 25 KTS AT 040100Z
   CIMSS AIDT: 33 KTS AT 040100Z
   CIMSS D-MINT: 39 KTS AT 031917Z
   CIMSS D-PRINT: 31 KTS AT 040100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 45-50 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 FORECASTED TO BEGIN ITS SHARP TRACK
CHANGE MOMENTARILY AND DRIVE WESTWARD ALONG THE NORTHERN EDGE OF A
SOUTHEASTWARD EXTENSION FROM A SUBTROPICAL RIDGE LOCATED OVER
WESTERN AUSTRALIA. THE WESTWARD TRACK FOR TC ALFRED WILL CONTINUE
THROUGH THE END OF THE FORECAST PERIOD AS THE SUBTROPICAL RIDGE
EXTENSION CONTINUES TO BUILD SOUTHEASTWARD. DURING THIS WESTWARD
PHASE TOWARD COASTAL AUSTRALIA, A SLIGHT INCREASE IN RIDGING
AMPLITUDE WILL CAUSE A RELATIVELY SMALL WEST-NORTHWESTWARD APPROACH
BETWEEN TAU 12 AND TAU 36. AFTER TAU 36, THE RIDGE WILL REORIENT
AND LEAD TO A WEST-SOUTHWESTWARD TRACK UNTIL TAU 72, WITH AN
EXPECTED LANDFALL NEAR TAU 66 NORTH OF BRISBANE. WITH REGARD TO
INTENSITY, TC 18P IS FORECASTED TO MAINTAIN INTENSITIES BETWEEN
50-55 KTS THROUGH TAU 48. FOLLOWING TAU 48, INTENSITIES ARE
EXPECTED TO WEAKEN SLIGHTLY AS THE SUPPORTIVE POLEWARD UPPER-LEVEL
OUTFLOW CHANNEL WEAKENS AND THE SYSTEMS WIND FIELD BEGINS TO
INTERACT WITH COASTAL AND INLAND TERRAIN. WITH THAT BEING SAID, THE
SYSTEM HAS ADOPTED SUBTROPICAL CYCLONE CHARACTERISTICS DUE TO
STRONG VWS AND DRY AIR ENTRAINMENT, HOWEVER, WARMING SEA SURFACE
TEMPERATURES ALONG THE AUSTRALIAN COASTLINE, AND DECREASING VWS
WILL ALLOW FOR AN INCREASINGLY SUPPORTIVE ENVIRONMENT FOR THE
CYCLONE TO REGAIN ITS SYMMETRICAL TROPICAL STRUCTURE JUST BEFORE
LANDFALL.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN TIGHT
AGREEMENT THAT A SHARP WESTWARD TURN IS EXPECTED OVER THE NEXT FEW
HOURS, WITH A CROSS-TRACK SPREAD OF JUST 46 NM AT TAU 48. AS THE
SYSTEM APPROACHES COASTAL AUSTRALIA, THE CROSS-TRACK SPREAD
INCREASES TO 64 NM NEAR TAU 66. DUE TO THE EXPECTED AND SHARP
WESTWARD TURN, WITH AN INCREASING CROSS-TRACK SPREAD JUST BEFORE
LANDFALL, THE JTWC FORECAST IS PLACED WITH MEDIUM CONFIDENCE AND
ALIGNED CLOSELY WITH THE JTWC CONSENSUS. WITH REGARD TO INTENSITY,
ALL INTENSITY CONSENSUS MEMBERS ARE IN AGREEMENT THAT INTENSITIES
WILL FLUCTUATE BETWEEN 50-55 KTS OVER THE NEXT 48 HOURS. FOLLOWING
TAU 48, EVERY NUMERICAL MODEL WITHIN THE INTENSITY CONSENSUS
INDICATES A WEAKENING PHASE JUST BEFORE LANDFALL. AFTER LANDFALL,
NUMERICAL MODELS WITHIN THE INTENSITY CONSENSUS INDICATE RAPID
WEAKENING BY TAU 72, LENDING MEDIUM CONFIDENCE TO THE JTWC
INTENSITY FORECAST.

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