WDXS32 PGTW 150300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING 
NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.7S 115.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 283 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE
DEEP FLARING CENTRAL CONVECTION SHEARED WESTWARD OF AND MOSTLY
OBSCURING THE LEVEL CIRCULATION CENTER (LLCC). THERE IS MODERATE
POLEWARD OUTFLOW BUT NO ORGANIZED CONVECTIVE FEEDER BANDS. ANALYSIS
INDICATES A MARGINAL ENVIRONMENT WITH VERY WARM SST AND MODERATE
POLEWARD OUTFLOW ALOFT OFFSET BY 20-25 KTS OF VERTICAL WIND SHEAR
(VWS). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
ON A MICROWAVE LLCC FEATURE IN THE 142218Z SSMIS IMAGE SUITE. THE
INITIAL INTENSITY IS ALSO PLACED WITH MEDIUM CONFIDENCE AND HELD
SLIGHTLY HIGHER THAN THE AGENCY AND OBJECTIVE DVORAK INTENSITY
ESTIMATES TO REFLECT THE SUSTAINED 6-HR CONVECTIVE SIGNATURE.

INITIAL WIND RADII BASIS: MOST RECENT STORM-CENTERED SCATTEROMETER
DATA. 


CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
SOUTHEAST ANCHORED OVER CENTRAL AUSTRALIA.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   DEMS: T2.0 - 30 KTS
   APRF: T1.5 - 25 KTS
   CIMSS ADT: 32 KTS AT 142020Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 18S WILL TRACK MORE SOUTHWESTWARD THEN
WEST-SOUTHWESTWARD AS THE
STR BUILDS AND EXTENDS WESTWARD. AS THE STORM MOTION BECOMES MORE
IN-PHASE WITH THE UPPER-LEVEL WIND FLOW, VWS IS EXPECTED TO
WEAKEN,
AND POLEWARD OUTFLOW TO IMPROVE, PROMOTING A STEADY
INTENSIFICATION, PEAKING 60KTS BY TAU 96. AFTERWARD, COLD DRY AIR
INTRUSION WILL MOSTLY BE RESPONSIBLE FOR A GRADUAL WEAKENING DOWN
TO 55KTS BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS EVENLY SPREAD OUT TO 150NM BY
TAU 72, LENDING MEDIUM CONFIDENCE TO THE NEAR- TO MID-PORTION OF
THE JTWC TRACK FORECAST. AFTERWARD, THE SPREAD BECOMES A LOT MORE
UNEVEN AND SIGNIFICANTLY WIDER TO 695NM BY TAU 120 WITH ECMWF ON
THE RIGHT AND NAVGEM ON THE LEFT
MARGIN OF THE MODEL ENVELOPE, LENDING LOW CONFIDENCE TO THE
EXTENDED PORTION OF THE JTWC TRACK FORECAST. 

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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