WDPS31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.7S 155.4E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 322 NM NORTH-NORTHEAST OF BRISBANE,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
SIGNIFICANTLY ERODING TROPICAL CYCLONE (TC) 18P (ALFRED), WITH
DISPLACED CONVECTION AND ELONGATING STRUCTURE. ANALYSIS REVEALS
THAT THE MID-LEVEL DRY AIR EXTENDING FROM THE SOUTHWEST, ALL THE
WAY TO THE EASTERN SECTOR OF TC ALFRED IS ERODING THE CONVECTIVE
STRUCTURE OF THE SYSTEM. COMBINED WITH MODERATELY STRONG,
NORTHWESTERLY VERTICAL WIND SHEAR (VWS), THE CENTRAL CONVECTION IS
BEING PUSHED AWAY FROM THE LOW-LEVEL CIRCULATION CENTER (LLCC),
WHILE THE SYSTEM STILL MAINTAINS SOME MOMENTUM FROM THE STRONG
DEVELOPMENT OVER THE PAST FEW DAYS. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE EXTRAPOLATION FROM 011032Z UHR
METOP-B ASCAT PASS. THE INITIAL INTENSITY OF 70 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT PASS, AS
WELL AS THE AGENCY FIXES AND OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   ABRF: T4.0 - 65 KTS
   CIMSS SATCON: 63 KTS AT 010927Z
   CIMSS ADT: 63 KTS AT 011130Z
   CIMSS AIDT: 57 KTS AT 011130Z
   CIMSS D-MINT: 72 KTS AT 010830Z
   CIMSS D-PRINT: 54 KTS AT 011300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ALMOST FULLY ENCIRCLING THE
SYSTEM

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 ALONG THE
SOUTHWESTERN PERIPHERY OF THE STR LOCATED TO THE NORTHEAST. AS THE
SYSTEM HEADS SOUTHEASTWARD OVER THE NEXT 48 HOURS IT WILL TRANSIT
THROUGH A MARGINAL TO MARGINALLY UNFAVORABLE ENVIRONMENT. WARM
(26-28 C) SEA SURFACE TEMPERATURES AND GOOD POLEWARD OUTFLOW
CONDITIONS WILL BE OFFSET BY SLIGHTLY INCREASING VWS AND
SIGNIFICANT DRY AIR INTRUSION. THEREFORE THE SYSTEM IS FORECAST
WEAKEN DOWN TO 55 KTS. AROUND TAU 48, THE STEERING PATTERN IS
FORECAST TO DRASTICALLY CHANGE. AS THE STR TO THE NORTHEAST MOVES
FURTHER NORTH, ANOTHER RIDGE THAT IS BUILDING OVER SOUTHEASTERN
AUSTRALIA, AND EXTENDING OFFSHORE, WILL ASSUME STEERING AND CAUSE
THE TC ALFRED TO MAKE A WESTWARD TURN. THROUGHOUT TAU 120 THE
SYSTEM IS FORECAST TO MAINTAIN INTENSITY AND HEAD TOWARDS
SOUTHEASTERN PORTION OF QUEENSLAND, AUSTRALIA.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT THROUGH THE INITIAL 48 HOURS OF THE FORECAST, WITH THE
CROSS-TRACK SPREAD OF 120 NM. AFTERWARDS, THE GUIDANCE DIFFUSES
SIGNIFICANTLY, AS THE MODELS RESPOND TO THE CHANGE IN STEERING
MECHANISM, WITH SIGNIFICANT UNCERTAINTY THROUGHOUT THE REMAINDER OF
THE FORECAST. BY TAU 120, THE CROSS TRACK SPREAD INCREASES TO 230
NM. THIS MEANS THAT AS THE SYSTEM REACHES COASTAL AUSTRALIA, IT CAN
MAKE LANDFALL ANYWHERE BETWEEN BRISBANE AND BARGARA, CAUSING THE
LONG TERM TRACK FORECAST TO BE LAID WITH LOW CONFIDENCE, WHILE THE
FIRST 72 HOURS ARE ASSESSED WITH MEDIUM CONFIDENCE AND PLACED IN
CLOSE PROXIMITY TO THE MULTI-MODEL CONSENSUS. THE OUTLIER MODELS IN
REGARD TO THE TRACK ARE UKMET ENSEMBLE TAKING THE TRACK INITIALLY
FURTHER AWAY FROM LAND, AND NAVGEM SUGGESTING A TRACK CLOSER TO THE
COAST. INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, AS ALL
MODELS SUGGEST SLIGHT WEAKENING TREND. AT TAU 36, AND THROUGHOUT
THE REMAINDER OF THE FORECAST HOWEVER, THE MODEL GUIDANCE IS
INCONSISTENT WITH HAFS AND COAMPS-TC PREDICTING SLIGHT UPTICK IN
INTENSITY, HWRF FORECASTING ADDITIONAL WEAKENING, WHILE GFS REMAINS
STEADY AT 55-60 KTS. THEREFORE, LONG TERM INTENSITY FORECAST IS
ASSESSED WITH LOW CONFIDENCE, BASED ON THE TRACK AND ASSOCIATED
MODEL GUIDANCE UNCERTAINTY.

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