WDPS31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.5S 156.2E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 254 NM NORTHEAST OF BRISBANE, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 18P (ALFRED) AS IT IS TRANSITING ALONG THE
SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE EAST. THE 
DEEP CONVECTION IS PUSHED AWAY FROM THE NEARLY FULLY EXPOSED LOW-LEVEL 
CIRCULATION CENTER (LLCC) BY THE MODERATELY STRONG (20-25 KTS) 
NORTHWESTERLY VERTICAL WIND SHEAR (VWS). ANALYSIS REVEALS MARGINAL 
ENVIRONMENT WITH WARM (26-27 C) SEA SURFACE TEMPERATURES (SST), STRONG 
POLEWARD OUTFLOW, OFFSET BY SIGNIFICANT DRY AIR INTRUSION PRESENT 
THROUGHOUT THE NORTHERN SEMICIRCLE OF THE SYSTEM. THE INITIAL POSITION 
IS PLACED WITH HIGH CONFIDENCE BASED ON THE SLIGHTLY ELONGATED LLCC
VISIBLE IN THE 021107Z METOP-C ASCAT PARTIAL PASS. THE INITIAL
INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED ASCAT SHOWING 45-50 KTS WINDS MAXIMA, COMBINED WITH
THE AGENCY DVORAK AND OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 44 KTS AT 020900Z
   CIMSS ADT: 32 KTS AT 021140Z
   CIMSS AIDT: 34 KTS AT 021140Z
   CIMSS D-MINT: 40 KTS AT 020814Z
   CIMSS D-PRINT: 33 KTS AT 021000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: 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 SOUTHEASTWARD
ALONG THE SOUTHWESTERN PERIPHERY OF THE STR THROUGH TAU 36, WITH
INTENSITY OSCILLATING BETWEEN 50 AND 55 KTS. AROUND TAU 48, THE
ENVIRONMENT WILL SIGNIFICANTLY CHANGE, WITH THE STEERING RIDGE TO
THE EAST PUSHING FURTHER NORTH AND ELONGATING. AT THE SAME TIME, AN
EXTENSION OF ANOTHER RIDGE OVER AUSTRALIA WILL ASSUME STEERING FOR
TC ALFRED, CHANGING THE MOVEMENT DIRECTION OF THE CYCLONE TO WESTWARD. 
BY TAU 48, THE SYSTEM WILL ALSO LOSE ITS MAIN OUTFLOW MECHANISM AS THE 
JET MAXIMA PREVIOUSLY LOCATED TO THE SOUTH SHIFTS EASTWARD. WITH TC 
18P NOW SOUTH OF THE 26S LATITUDE, THE SEA SURFACE TEMPERATURES WILL
DROP TO 25-26 C, WHILE THE VWS INCREASES TO 25+ KTS. AS A RESULT,
THE SYSTEM WILL BEGIN TO WEAKEN AS IT TRANSITS TOWARD THE COAST OF
AUSTRALIA. THE SYSTEM IS FORECAST TO MAKE LANDFALL JUST NORTH OF
BRISBANE AND DISSIPATE BY TAU 120.

MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS IN FAIR
AGREEMENT, WITH MORE MODELS TIGHTLY PACKED CLOSE TO THE MULTI-MODEL
CONSENSUS, RESULTING IN A 75 NM CROSS-TRACK SPREAD AT TAU 36,
EXTENDING TO JUST 90 NM AT LANDFALL. THE TIMING OF THE TURN REMAINS
UNCERTAIN, WITH GFS ENSEMBLE PROJECTING THE QUICKEST TURN TOWARDS
THE COAST, WHILE ECMWF ENSEMBLE IS THE SLOWEST TRACKER TO MAKE THE
TURN. IN REGARD TO LANDFALL, MAJORITY OF THE MODELS ARE TIGHTLY
PACKED AND SUGGEST A TRACK 20-30 NM NORTH OF BRISBANE WITH A
CROSS-TRACK SPREAD OF 40 NM. THE ONLY OUTLIER IS NAVGEM WHICH
PREDICTS LANDFALL APPROXIMATELY 40 NM SOUTH OF BRISBANE. JTWC TRACK
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE AND CLOSE TO THE
MULTI-MODEL CONSENSUS. IN TERMS OF INTENSITY, ALL CONSENSUS MEMBER
SUGGEST A SLIGHT INTENSIFICATION OVER THE NEXT 24 HOURS, WITH THE
SYSTEM MAINTAINING INTENSITY UNTIL THE CHANGES IN THE ENVIRONMENT 
OCCUR BY TAU 48. AFTERWARDS, ALL MODELS SUGGEST A RAPID AND STEADY
WEAKENING CULMINATING IN DISSIPATION OVER LAND BY TAU 120. JTWC
INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE THROUGHOUT
THE FORECAST, AS THE MODELS GENERALLY AGREE ON THE INTENSIFICATION
AND WEAKENING TRENDS, BUT THE TRACK GUIDANCE SPREAD INCREASES 
UNCERTAINTY.

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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