WDXS32 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING 
NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1S 114.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 312 NM NORTH OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LOW-LEVEL
CLOUD BANDS WRAPPING INTO TROPICAL CYCLONE 18S, THOUGH THE LOW
LEVEL CIRCULATION CENTER (LLCC) REMAINS OBSCURED BY PLUMES OF
FLARING CONVECTION. AS EASTERLY VERTICAL WIND SHEAR (VWS) HAS
DECREASED OVER THE LAST SIX HOURS TO 15-20KTS, THE VERTICAL
STRUCTURE OF THE SYSTEM HAS IMPROVED SLIGHTLY. THE SYSTEM REMAINS
QUASI-STATIONARY (QS) IN THE REGION, CONTINUING OCEANIC UPWELLING
AND DRAINING THE OCEAN HEAT CONTENT. THE SYSTEM HAS DRIFTED TO THE
SOUTHEAST WHILE REMAINING IN A COMPETING STEERING ENVIRONMENT ON
THE SOUTHERN PERIPHERY OF A NEAR EQUATORIAL RIDGE (NER) TO THE
NORTH AND A SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. OUTFLOW WAFTS
WEAKLY POLEWARD AS WINDS ARE NOT VERY DIVERGENT ALOFT. THE INITIAL
POSITION WAS ASSESSED WITH LOW CONFIDENCE BASED ON ANIMATED MSI
DEPICTING WELL-DEFINED CLOUD BANDS WRAPPING FROM THE NORTHWEST INTO
A CENTER BENEATH THE CONVECTION. THE INTENSITY WAS ASSESSED WITH
LOW CONFIDENCE BASED ON AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   APRF: T1.5 - 25 KTS
   CIMSS ADT: 51 KTS AT 170000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   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 IS FORECAST TO REMAIN IN A QS STATE FOR
THE NEXT 48 HOURS BEFORE BEING DRIVEN WESTWARD BY A BUILDING NER TO
THE SOUTHEAST OVER CONTINENTIAL AUSTRALIA. AS THE SYSTEM PICKS UP
TRACK SPEED BY TAU 72, THE SYSTEM IS EXPECTED TO REACH 8KTS BY THE
END OF THE FORECAST PERIOD. TC 18S IS FORECAST TO STRUGGLE TO
INTENSIFY IN THE NEAR-TERM AND REMAIN ALMOST STAGNANT FOR THE FIRST
24 HOURS. AS THE SYSTEM MOVES AWAY FROM THE REGION BETWEEN TAU
48-72, VWS SHOULD REMAIN FAVORABLE ALLOWING FOR SLOW
INTENSIFICATION DESPITE CONTINUING INTO A REGION OF RELATIVELY
COOLER WATERS AND LOWER OCEAN HEAT CONTENT. BY THE END OF THE
FORECAST PERIOD, THE SYSTEM IS EXPECTED TO INCREASE TO A PEAK OF
45KTS AS THE ENVIRONMENT IMPROVES. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GENERALLY GOOD
AGREEMENT THAT THE SYSTEM WILL REMAIN QUASI-STATIONARY BEFORE
TRACKING TO THE WEST BETWEEN THE 48-72 HOUR POINT. THE MAXIMUM
CROSS TRACK SPREAD BY THE END OF THE FORECAST OPENS TO 400NM BY THE
END OF THE FORECAST PERIOD, WITH ECM2 TO THE NORTH AND NAVGEM TO
THE SOUTH. THE INTENSITY GUIDANCE HAS CHANGED DRASTICALLY OVER THE
LAST SIX HOURS, WITH HAFS-A DROPPING FROM A PEAK OF 150KTS ON THE
161200Z RUN TO A PEAK OF 40KTS IN THE CURRENT RUN. JTWC SHIPS
GUIDANCE AND HWRF BOTH REMAIN HIGH, PEAKING AT 85KTS BY TAU 120.
THE SIGNIFICANT DEVIATION BETWEEN MODEL RUNS HAS CAUSED GREAT
UNCERTAINTY AND LOW CONFIDENCE IN THE INTENSITY FORECAST.

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