WDXS31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.9S 127.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 220 NM WEST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A CONSOLIDATING 
SYSTEM WITH EXPANSIVE SPIRAL BANDING FROM ALL QUADRANTS BEGINNING TO 
TAKE SHAPE AND FEEDING INTO THE COLD DENSE OVERCAST THAT IS OBSCURING 
THE LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH 
MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM LOW CLOUD LINES 
WRAPPING TOWARD THE LLC. THE INITIAL INTENSITY IS BASED WITH HIGH 
CONFIDENCE FROM THE AUTOMATED DVORAK ESTIMATE AND CONSISTENT WITH THE 
IMPROVEMENT IN THE EIR CONVECTIVE SIGNATURE OVER THE PAST SIX HOURS. 
TC 18S IS IN A FAVORABLE ENVIRONMENT WITH LIGHT-MODERATE VWS, STRONG 
POLEWARD OUTFLOW AND VERY WARM ALONG-TRACK SST.

INITIAL WIND RADII BASIS: PERSISTENCE. 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   CIMSS ADT: 41 KTS AT 082330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   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 CONTINUE TO TRACK SOUTHWESTWARD
UNDER THE STEERING STR TOWARD THE SOUTH INDIAN OCEAN. AFTER TAU 72,
A TRANSITORY SHORTWAVE TROUGH APPROACHING FROM THE SOUTHWEST WILL
ERODE THE STR AND ALLOW THE CYCLONE TO RECURVE SOUTHEASTWARD, MAKE
LANDFALL JUST EAST OF PORT HEADLAND SHORTLY AFTER TAU 96, AND TRACK
INLAND OVER WESTERN AUSTRALIA. THE FAVORABLE ENVIRONMENT WILL
INITIALLY PROMOTE GRADUAL INTENSIFICATION TO 80KTS BY TAU 48.
AFTERWARD, LOW VWS AND VERY WARM SST IN THE INDIAN OCEAN WILL FUEL
A RAPID INTENSIFICATION (RI) TO A PEAK OF 130KTS BY TAU 96, RIGHT
BEFORE LANDFALL. AFTER LANDFALL, INTERACTION WITH THE TERRAIN WILL
REDUCE THE INTENSITY TO 45KTS BY TAU 120 AS IT STARTS DISSIPATING
OVER LAND.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT
WITH THE LAID-OUT FORECAST TRACK, GRADUALLY SPREADING OUT TO A
MAXIMUM OF 260NM BETWEEN TAU 72 AND TAU 96, WITH NAVGEM THE NOTABLE
LEFT-OF-TRACK OUTLIER. THERE IS HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST UP TO TAU 72, THEN LOW AFTERWARD DUE TO THE LAND PASSAGE.
THERE IS MEDIUM CONFIDENCE IN THE INTENSITY FORECAST UP TO TAU 72
THEN LOW CONFIDENCE AFTERWARD ON ACCOUNT OF THE HIGH VARIABILITY IN
THE INTENSITY GUIDANCE ASSOCIATED WITH RI. 

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