WDXS32 PGTW 302100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12S (ELVIS)      
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.5S 46.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 564 NM SOUTHEAST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BROAD,
EXPOSED LOW-LEVEL CIRCULATION (LLC), WITH RAPIDLY DETERIORATING
DEEP CONVECTION SHEARED OVER THE SOUTHEAST QUADRANT OF THE LLC. A
301606Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE CAUGHT THE EARLY 
STAGES OF THE DECOUPLING WITH THE LLCC BECOMING EXPOSED ON THE 
NORTHWESTERN EDGE OF THE UPPER-LEVEL CIRCULATION CENTER. DESPITE THE 
DECAYING CONVECTIVE STRUCTURE AND DECREASING DVORAK DATA-T ESTIMATES, 
THE 301534Z RCM-2 SAR IMAGE REVEALS 25-30 KNOT WINDS, WITH A SWATH OF 
35-45 KNOT WINDS OVER THE SOUTHEASTERN QUADRANT. CONSEQUENTLY, THE 
INITIAL INTENSITY IS HELD AT 40 KNOTS WITH HIGH CONFIDENCE. 
ENVIRONMENTAL CONDITIONS HAVE DEGRADED, WITH HIGH (25-30 KNOTS) 
VERTICAL WIND SHEAR (VWS) AND COOLING SEA SURFACE TEMPERATURES OFFSET 
SOMEWHAT BY STRONG POLEWARD OUTFLOW ENHANCED BY THE JET TO THE SOUTH. 
EXTENSIVE DRY AIR IS PRESENT OVER THE WESTERN AND NORTHERN 
SEMICIRCLES, ENTRAINING INTO THE SYSTEM'S CORE. ADDITIONALLY, STRONG 
COLD AIR ADVECTION IS OCCURRING OVER THE WESTERN PERIPHERY OF THE 
SYSTEM, WITH EXTENSIVE STRATOCUMULUS EVIDENT IN EIR IMAGERY.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) 
POSITIONED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS ADT: 34 KTS AT 301500Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) ELVIS IS TRACKING UNDER
THE EASTERN PERIPHERY OF AN APPROACHING SUBTROPICAL TROUGH WITH
STRONG BAROCLINICITY WHILE EXHIBITING SOME CHARACTERISTICS OF A
SUBTROPICAL CYCLONE. HOWEVER, THE SYSTEM IS EXPECTED TO COMMENCE
EXTRA-TROPICAL TRANSITION AND RAPIDLY TRANSITION INTO AN EXTRA-
TROPICAL LOW WITHIN THE NEXT 36 HOURS, GAINING FRONTAL 
CHARACTERISTICS AS IT TRACKS UNDER THE JET BY TAU 36. THE GENERAL
TRACK FORECAST IS SOUTHEASTWARD THROUGH THE FORECAST PERIOD, WITH
THE STR TO THE NORTHEAST DRIVING THE SYSTEM POLEWARD OVER COLD WATER 
(19-20C) AND VERY STRONG VWS (30-40 KNOTS) BY TAU 36.        

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT WITH AN 85NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU 36.
THE 300600Z ECMWF ENSEMBLE (EPS) AND THE 301200Z GFS ENSEMBLE
(GEFS) ARE ALSO IN TIGHT AGREEMENT SUPPORTING THE JTWC FORECAST
TRACK WITH HIGH CONFIDENCE. RELIABLE INTENSITY GUIDANCE IS IN FAIR
AGREEMENT, WITH SLIGHT WEAKENING OVER THE NEXT 24 HOURS THEN
REINTENSIFICATION TO 40-45 KNOTS AS AN EXTRA-TROPICAL LOW AFTER TAU
36.     

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