WDXS31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (NEVILLE)   
WARNING NR 040//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5S 93.8E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 1138 NM WEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
INCREASINGLY ASYMMETRIC SYSTEM AS WARMING CONVECTIVE TOPS AND VERTICAL 
WIND SHEAR (VWS) HAVE BECOME EVIDENT OVER THE LAST 12 HOURS. THE 
RECENTLY OBSERVED EYE FEATURE ON ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) HAS SINCE BECOME COMPLETELY OBSCURED AS THE ENVIRONMENT 
CONTINUES TO BECOME LESS CONDUCIVE FOR TC SUSTAINMENT. NORTH-
NORTHEASTERLY VWS OF 20-25 KTS HAS INCREASED SINCE THE PREVIOUS 
WARNING AS TEMPERATURE GRADIENTS HAVE TIGHTENED SIGNIFICANTLY ALONG 
THE NORTH-NORTHEASTERN EDGE OF THE CYCLONE, WITH UPPER-LEVEL 
CONVECTIVE TOPS BECOMING DIFFUSE SOUTHWARD OF THE SYSTEM THROUGH THE 
PAST FEW HOURS. AS TC 18S CONTINUED SOUTHWESTWARD, AN INCREASING COLD-
AIR STRATOCUMULUS DECK HAS WRAPPED AROUND THE WESTERN AND NORTHERN 
PERIPHERY OF THE SYSTEM'S CIRCULATION. THE INITIAL POSITION IS PLACED 
WITH HIGH CONFIDENCE BASED ON A MICROWAVE EYE FEATURE
INDICATED ON THE 231018Z 37 GHZ SSMIS MICROWAVE IMAGE. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON UW-CIMSS
OBJECTIVE INTENSITY ESTIMATES AND SUBJECTIVE INTENSITY ESTIMATES
LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK.

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF THE DEEP-LAYER
SUBTROPICAL RIDGE (STR) LOCATED IN THE SOUTHEASTERN INDIAN OCEAN.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T5.0 - 90 KTS
   APRF: T4.0 - 65 KTS
   CIMSS SATCON: 69 KTS AT 230800Z
   CIMSS ADT: 77 KTS AT 231200Z
   CIMSS AIDT: 70 KTS AT 231200Z
   CIMSS DPRINT: 75 KTS AT 231200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 24-26 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 TRACKING ALONG THE WESTERN PERIPHERY
OF A DEEP-LAYER STR LOCATED IN THE SOUTHEASTERN INDIAN OCEAN (IO).
AFTER TAU 30, THE CYCLONE WILL MOVE SOUTHWESTWARD TO SOUTHWARD UNDER 
THE EASTWARD PROGRESSING MID-LATITUDE LONGWAVE TROUGH. OVER THE NEXT 
48 HOURS, ENVIRONMENTAL CONDITIONS WILL CONTINUE TO BECOME LESS-
CONDUCIVE FOR WARM-CORE BAROTROPIC SYSTEM SUSTAINMENT, AS COOL, DRY 
AIR WRAPS COMPLETELY INTO THE CORE STRUCTURE AND VWS CONTINUES AT 20-
25 KTS INTO TAU 24, AND THEN INCREASES TO 30-35 KTS BY TAU 48. BY THE 
END OF THE FORECAST PERIOD, COMPLETE DISSIPATION OF TC 18S IS EXPECTED 
AS INTENSITIES DECREASE TO 30 KTS. 

MODEL DISCUSSION: THE DETERMINISTIC MODELS ARE IN GOOD AGREEMENT
THAT TC 18S WILL CONTINUE TO TRACK GENERALLY SOUTHWESTWARD THROUGH
TAU 48. EXCLUDING NAVGEM, THE JTWC TRACK CONSENSUS MEMBERS ARE
SHOWING A CROSS-TRACK SPREAD OF 64 NM BY TAU 36 AND INCREASING TO
73 NM BY TAU 48. WHILE THE CYCLONE PROGRESSES TOWARD THE MID-LATITUDE 
PATTERN, A RAPID WEAKENING TREND IS ILLUSTRATED BY THE JTWC INTENSITY 
CONSENSUS AIDS WHICH REMAIN IN TIGHT AGREEMENT THAT INTENSITIES WILL 
QUICKLY DECREASE TO LESS THAN TC WARNING THRESHOLD (35 KTS) BY THE END 
OF THE FORECAST PERIOD. 

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