WDXS32 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10S (SEAN)      
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.3S 110.0E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 235 NM WEST-SOUTHWEST OF LEARMONTH,
                         AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AFTER UNDERGOING AN EYEWALL REPLACEMENT CYCLE, TROPICAL CYCLONE
(TC) 10S TRACKED OVER COOLER SST (25-26C) AND WEAKENED SIGNIFICANTLY. 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS RAPID 
DECAY OF THE EYEWALL AND LOSS OF THE EYE (AROUND 201630Z), WITH DEEP 
CONVECTION BECOMING INCREASINGLY DISORGANIZED. MICROWAVE IMAGERY IS 
LIMITED; HOWEVER, A 201805Z ATMS 89GHZ MICROWAVE IMAGE REVEALS A 
DEFINED LOW-LEVEL CIRCULATION CENTER POSITIONED ON THE NORTHWEST EDGE 
OF THE REMNANT EYEWALL, WITH SHALLOW CONVECTION OVER THE WESTERN 
SEMICIRCLE INDICATIVE OF THE RAPID WEAKENING TREND. ROBUST RADIAL 
OUTFLOW HAS PERSISTED, MAINTAINING THE RAPIDLY DWINDLING CORE 
CONVECTION. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE 
BASED ON THE EIR IMAGERY AND THE ATMS IMAGE. THE INITIAL INTENSITY OF 
105 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE DVORAK 
CURRENT INTENSITY ESTIMATES RANGING FROM 5.0-6.0 (90-115 KNOTS) AS 
WELL AS THE CIMSS ADT AND SATCON OBJECTIVE ESTIMATES (100-102 KNOTS).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
ENTRENCHED OVER WESTERN AUSTRALIA.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   DEMS: T6.0 - 115 KTS
   APRF: T5.0 - 90 KTS
   CIMSS SATCON: 100 KTS AT 201800Z
   CIMSS ADT: 102 KTS AT 201800Z
   CIMSS AIDT: 91 KTS AT 201800Z
   CIMSS D-PRINT: 90 KTS AT 201800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 10S WILL TRACK SOUTHWESTWARD THROUGH TAU 24
THEN TURN SOUTHWARD THROUGH TAU 48 AS IT TRACKS ALONG THE WESTERN
PERIPHERY OF THE STR. SST VALUES WILL COOL STEADILY FROM ABOUT 25C
TO 22C BY TAU 48. STRONG VERTICAL WIND SHEAR (VWS) AND DRY AIR 
ENTRAINMENT WILL FURTHER DEGRADE ENVIRONMENTAL CONDITIONS AFTER TAU 
24 SUPPORTING A RAPID WEAKENING TREND. AFTER TAU 48, THE SYSTEM WILL 
RECURVE SOUTH-SOUTHEASTWARD AROUND THE SOUTHERN PERIPHERY OF THE STR, 
ENCOUNTERING STRONG WESTERLIES AND VWS ASSOCIATED WITH THE 
SUBTROPICAL JET. TC 10S WILL ENTER A VERY DRY ENVIRONMENT AND TRACK 
OVER COLD SST VALUES NEAR 20C, WHICH WILL LEAD TO DISSIPATION BY TAU 
72.    

MODEL DISCUSSION: DETERMINISTIC GUIDANCE IS NOW IN TIGHT AGREEMENT
THROUGH TAU 48, WITH A 50NM CROSS-TRACK SPREAD AT TAU 48, DIVERGING
TO ABOUT 110NM BY TAU 72. PROBABILISTIC GUIDANCE IS ALSO IN TIGHT
AGREEMENT THROUGH TAU 48, WITH INCREASING SPREAD AFTER TAU 48.
OVERALL TRACK CONFIDENCE IS ASSESSED AT HIGH.     

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