WDXS31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (NEVILLE)    
WARNING NR 031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.7S 109.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 375 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 18S HAS CONTINUED TO CONSOLIDATE QUICKLY WITH
A FAIRLY IMPRESSIVE PRESENTATION IN THE ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI), WHICH SHOWS TIGHTLY CURVED BANDING AND 
STRONG MID-LEVEL TURNING. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY DEPICTS A MORE RAGGED APPEARANCE, BUT CLEARLY SHOWS A 
CONSOLIDATING CORE. A RECENT 200227Z ASCAT-B IMAGE SUGGESTS THE LOW-
LEVEL WIND FIELD IS LAGGING SLIGHTLY BEHIND THE MSI STRUCTURE, WITH 
30-35 KNOT WINDS OVER THE SOUTHERN SEMICIRCLE. THE 200449Z GMI 89 GHZ 
AND 37 GHZ IMAGES INDICATE A SLIGHT TILT TO THE VORTEX, WITH THE 
UPPER-LEVEL CIRCULATION CENTER DISPLACED ABOUT 6 NM SSE OF THE LOW-
LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH 
HIGH CONFIDENCE BASED ON THE WELL-DEFINED LLCC EVIDENT IN THE GMI 37 
GHZ IMAGE. UPPER-LEVEL CONDITIONS CONTINUE TO IMPROVE WITH LOW 
VERTICAL WIND SHEAR AND RADIAL OUTFLOW. THE INITIAL INTENSITY IS 
ASSESSED AT 40 KNOTS BASED ON AN AVERAGE OF THE BULK OF THE 
SUBJECTIVE DVORAK AND CIMSS OBJECTIVE INTENSITY ESTIMATES RANGING 
FROM 34 TO 45 KNOTS.        

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 44 KTS AT 200430Z
   CIMSS ADT: 39 KTS AT 200600Z
   CIMSS AIDT: 34 KTS AT 200600Z
   CIMSS DPRINT: 44 KTS AT 200600Z
   CIMSS DMINT: 52 KTS AT 200448Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING. 

FORECAST DISCUSSION: TC 18S WILL TRACK WESTWARD TO WEST-SOUTHWESTWARD 
ALONG THE NORTHERN PERIPHERY OF THE STR THROUGH TAU 72 WHILE BECOMING 
VERTICALLY ALIGNED AND RAPIDLY INTENSIFYING TO A PEAK INTENSITY OF 90 
KNOTS UNDER FAVORABLE UPPER-LEVEL CONDITIONS. AFTER TAU 72, THE 
SYSTEM WILL BEGIN TO ROUND THE NORTHWESTERN PERIPHERY OF THE STR, 
INTERACTING WITH A SHARP SUBTROPICAL UPPER-LEVEL TROUGH. AS THE 
SYSTEM RECURVES AROUND THE STR, IT WILL TRACK UNDER THE LEADING EDGE 
OF THE AFOREMENTIONED SUBTROPICAL TROUGH, WITH INCREASING 
NORTHWESTERLY VERTICAL WIND SHEAR (20-30 KNOTS), COOLING SEA SURFACE 
TEMPERATURES (24 TO 26 C) AND SIGNIFICANT DRY AIR ENTRAINMENT 
CONTRIBUTING TO RAPID WEAKENING. THE SYSTEM WILL BEGIN TO DISSIPATE 
NEAR TAU 120 AND WILL LIKELY DISSIPATE PRIOR TO COMPLETING 
SUBTROPICAL TRANSITION.     

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, NUMERICAL MODEL
GUIDANCE REMAINS IN TIGHT AGREEMENT THROUGH TAU 72, WITH A 90 NM
CROSS-TRACK SPREAD AT TAU 72. AFTER TAU 72, NUMERICAL GUIDANCE
DIVERGES GRADUALLY, WITH A 180 NM CROSS-TRACK SPREAD AT TAU 120.
MESOSCALE GUIDANCE SUPPORTS RAPID INTENSIFICATION OVER THE NEXT 2-3
DAYS, WITH HAFS-A INDICATING A PEAK INTENSITY OF 103 KNOTS AT TAU
60 AND COAMPS-TC (GFS VERSION) PEAKING AT 90 KNOTS AT TAU 48.
ALTHOUGH NO RAPID INTENSIFICATION AIDS HAVE TRIGGERED YET, THE
200000Z COAMPS-TC INTENSITY PROBABILITY PLOT INDICATES A 40 TO 50
PERCENT PEAK PROBABILITY OF RAPID INTENSIFICATION OCCURRING OVER
THE NEXT TWO DAYS.   

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