WDXS31 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.6S 123.4E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 267 NM NORTH-NORTHEAST OF BROOME,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A
MEDIUM-SIZED
SYSTEM WITH FLARING CENTRAL CONVECTION AND FRAGMENTED SPIRAL
BANDING FEEDING IN FROM ALL QUADRANTS INTO THE COLD DENSE OVERCAST
THAT IS OBSCURING THE LOW LEVEL CIRCULATION. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM NOTCH
FEATURE IN THE 092213Z SSMIS 37GHZ MICROWAVE IMAGE. THE INITIAL
INTENSITY IS
BASED WITH MEDIUM CONFIDENCE FROM AN OVERALL ASSESSMENT OF AGENCY
AND AUTOMATED DVORAK ESTIMATES AND CONSISTENT WITH THE IMPROVED
CONVECTIVE SIGNATURE OVER THE PAST SIX HOURS. TC 18S IS IN A 
FAVORABLE ENVIRONMENT WITH LIGHT 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: T3.5 - 55 KTS
   KNES: T3.0 - 45 KTS
   WIIX: T3.0 - 45 KTS
   CIMSS ADT: 39 KTS AT 092330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: LOW

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 IN THE SOUTH INDIAN OCEAN. AFTER TAU 48, 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 JUST AFTER TAU 72, AND TRACK
INLAND OVER WESTERN AUSTRALIA. THE FAVORABLE ENVIRONMENT WILL
INITIALLY PROMOTE GRADUAL INTENSIFICATION TO 85KTS BY TAU 36.
AFTERWARD, LOW VWS, INCREASED OUTFLOW AHEAD OF THE SHORTWAVE
TROUGH, AND VERY WARM SST IN THE INDIAN OCEAN WILL FUEL A RAPID
INTENSIFICATION (RI) TO A PEAK OF 130KTS BETWEEN TAU 48 AND TAU 72.
AFTER LANDFALL, INTERACTION WITH THE TERRAIN WILL REDUCE THE
INTENSITY TO 55KTS BY TAU 96 THEN TO DISSIPATION BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL TIGHT AGREEMENT
WITH THE LAID-OUT FORECAST TRACK, GRADUALLY SPREADING OUT TO A JUST
165NM BY TAU 120. IN VIEW OF THIS, 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//
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