WDXS31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (NEVILLE) 
WARNING NR 038//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.4S 99.5E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 854 NM WEST-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS TROPICAL
CYCLONE (TC) 18S (NEVILLE) WITH A DEGRADING RAGGED-EYE THAT HAS 
NEARLY FILLED AS THE SYSTEM WEAKENS. THE CURRENT ENVIRONMENT IS
ASSESSED AS MARGINALLY UNFAVORABLE CHARACTERIZED BY MODERATE
POLEWARD OUTFLOW ALOFT AND WARM (27-28 C) SEA SURFACE TEMPERATURES
GREATLY OFFSET BY MODERATE TO HIGH (20-25 KTS) VERTICAL WIND SHEAR
(VWS) AND DRY AIR BEGINNING TO ENTRAIN INTO THE SYSTEM. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 221200Z
HIMAWARI-9 INFRARED SATELLITE IMAGE. THE INITIAL INTENSITY OF 90 KTS 
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON OBJECTIVE AND SUBJECTIVE
INTENSITY ESTIMATES LISTED BELOW. THE CURRENT INTENSITY (CI) DVORAK
ESTIMATES ARE ASSESSED AS POTENTIALLY TOO HIGH DUE TO THE COMPACT 
NATURE AND SIZE OF THE SYSTEM. FINAL-T NUMBERS RANGING FROM 4.5-5.0 
ARE ASSESSED TO BE MORE REPRESENTATIVE AND WERE LEVIED MORE WHEN 
DETERMINING SYSTEM INTENSITY.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   APRF: T5.5 - 102 KTS
   CIMSS DPRINT: 95 KTS AT 221200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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: TC 18S IS FORECAST TO CONTINUE ON A
WEST-SOUTHWESTWARD TRACK THROUGH TAU 48 AS IT TRACKS ALONG THE
NORTHWESTERN PERIPHERY OF THE STR TO THE SOUTH. AFTER TAU 48, THE
SYSTEM IS FORECAST TO TURN MORE POLEWARD (SOUTHWESTWARD) AS 18S 
ROUNDS THE WESTERN EXTENT OF THE STR. REGARDING INTENSITY, TC 18S IS 
EXPECTED TO CONTINUE TO WEAKEN AS VWS VALUES REMAIN HIGH, SEA
SURFACE TEMPERATURES DECREASE, AND DRY AIR ENTRAINS THE SYSTEM.
ADDITIONALLY, A PRONOUNCED SHORTWAVE TROUGH IS POSITIONED TO THE
WEST AND WILL AID IN DISSIPATION AS 18S ENCROACHES THE TROUGH. THE 
SYSTEM IS FORECAST TO WEAKEN TO 70 KTS NEAR TAU 12, 60 KTS NEAR TAU 
24, 50 KTS NEAR TAU 36, AND 40 KTS NEAR TAU 48. BY TAU 72, TC 18S IS
ANTICIPATED TO HAVE ENTIRELY DISSIPATED.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN CLOSE AGREEMENT
WITH A 90 NM CROSS-TRACK SPREAD AT TAU 72. AS A RESULT, THE
JTWC FORECAST TRACK WAS PLACED WITH HIGH CONFIDENCE THROUGH THE
FORECAST PERIOD. INTENSITY GUIDANCE IS IN FAIR AGREEMENT, WITH ALL
MODELS SUGGESTING A WEAKENING TREND AND DISSIPATION BY TAU 72. HWRF
SLIGHTLY DIFFERS BY MAINTAINING 90 KTS THROUGH TAU 12 BEFORE
STARTING THE WEAKENING TREND. HAFS-A DEPICTS A QUICKER ONSET OF
DISSIPATION, REACHING 25 KTS BY TAU 48. THE JTWC INTENSITY FORECAST
IS THEREFORE PLACED WITH MEDIUM CONFIDENCE THROUGH THE FORECAST
PERIOD. 

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