WDXS31 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (ILSA) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
 
SUMMARY:
   INITIAL POSITION: 17.7S 119.1E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 394 NM NORTHEAST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET
 
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A LARGE,
HIGHLY SYMMETRICAL SYSTEM WITH A DIMPLED EYE. CENTRAL CONVECTION
RAPIDLY DEEPENED AND RAIN BANDS WRAPPED TIGHTER INTO THE CENTER
OVER THE LAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED
ON THE DIMPLED EYE, ADJUSTED FOR A SLIGHT WESTWARD TILT. THE
INITIAL INTENSITY OF 115KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE HIGH END OF AUTOMATED INTENSITY ESTIMATES OPEN-AIIR
AND DMN THAT ARE MORE IN LINE WITH THE IMPROVED 6-HR CONVECTIVE
SIGNATURE. THE ENVIRONMENT REMAINS HIGHLY FAVORABLE WITH STRONG
RADIAL OUTFLOW AND VERY WARM SST OFFSETTING THE MEDIUM VWS.
 
INITIAL WIND RADII BASIS: PERSISTENCE.
 
CURRENT STEERING MECHANISM:  DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE EAST.
 
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 103 KTS AT 122018Z
   CIMSS ADT: 90 KTS AT 122330Z
 
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG RADIAL
 
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: A SHORTWAVE TROUGH APPROACHING FROM THE
SOUTHWEST HAS BEGUN TO WEAKEN THE STEERING STR. THIS WILL ALLOW THE
CYCLONE TO TRACK SOUTHWARD THEN SOUTHEASTWARD, MAKING LANDFALL
APPROXIMATELY 90NM ENE OF PORT HEADLAND SHORTLY BEFORE TAU 18, THEN
TRACK RAPIDLY INTO THE CENTRAL AUSTRALIAN OUTBACK. THE HIGHLY
FAVORABLE CONDITIONS, COUPLED WITH INCREASED EASTWARD OUTFLOW
ASSOCIATED WITH THE STRONG WESTERLIES AHEAD OF THE TROUGH, WILL
SUSTAIN ITS RAPID INTENSIFICATION (RI) TO A PEAK OF 130KTS BY TAU
12 PRIOR TO LANDFALL. AFTERWARD, INCREASING VWS AND LAND
INTERACTION WILL RAPIDLY ERODE THE SYSTEM TO DISSIPATION BY TAU 48.
 
 
MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT WITH
AN EVEN SPREAD TO 230NM BY TAU 48, LENDING HIGH CONFIDENCE IN THE
JTWC TRACK FORECAST. THERE IS ONLY MEDIUM CONFIDENCE IN THE
INTENSITY FORECAST DUE TO THE VARIABLES ASSOCIATED WITH RI AND LAND
PASSAGE.
 
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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