WDXS31 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FYTIA) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.3S 54.0E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 183 NM SOUTH-SOUTHWEST OF ST DENIS
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 19S HAS HELD FAIRLY STEADY OVER THE MUCH OF THE PAST TWELVE
HOURS BUT IS BEGINNING TO SHOW SIGNS OF RAPID STRUCTURAL CHANGE.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION SHEARING EASTWARD AS THE SYSTEM ENCOUNTERS STRONG
UPPER-LEVEL WESTERLY FLOW ASSOCIATED WITH AN UPPER-LEVEL TROUGH
APPROACHING FROM THE SOUTHWEST. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON 022144Z ATMS 89 GHZ MICROWAVE SATELLITE
IMAGERY AND A 022330Z PGTW SATELLITE FIX. THE INITIAL INTENSITY OF
55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF
SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS SATCON: 51 KTS AT 022146Z
   CIMSS ADT: 49 KTS AT 022100Z
   CIMSS AIDT: 40 KTS AT 022000Z
   CIMSS D-MINT: 33 KTS AT 022146Z
   CIMSS D-PRINT: 53 KTS AT 022330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 19S WILL LIKELY CONTINUE TO TRACK 
SOUTHEASTWARD THROUGH THE FORECAST PERIOD UNDER THE STEERING 
INFLUENCE OF SUBTROPICAL RIDGING TO THE EAST. AS THE SYSTEM MOVES 
POLEWARD, AN UPPER-LEVEL TROUGH CURRENTLY ANALYZED TO THE SOUTHWEST 
WILL ENVELOPE THE SYSTEM. INCREASING VERTICAL WIND SHEAR AND DRY
AIR ENTRAINMENT DRIVEN BY INTERACTION WITH THE TROUGH WILL RESULT IN 
STEADILY WEAKENING. TC 19S IS EXPECTED TO BEGIN SUBTROPICAL
TRANSITION SHORTLY AFTER TAU 24, WHICH WILL SHOULD PROVIDE AN 
INJECTION OF BAROCLINIC ENERGY TO SUPPORT SUSTAINMENT OF GALE FORCE 
LOW-LEVEL WIND SPEEDS, ALTHOUGH DISSIPATION IS ALSO POSSIBLE. 
TRANSITION TO A SUBTROPICAL LOW IS EXPECTED TO COMPLETE BY TAU 48.

MODEL DISCUSSION: CONSENSUS MODEL GENERALLY AGREE ON A
SOUTHEASTWARD TRACK, THROUGH SPREAD IS EVIDENT IN DEPICTIONS OF
TRACK SPEED AND INTENSITY AS THE SYSTEM UNDERGOES RAPID STRUCTURAL
CHANGE. TWO SCENARIOS CHARACTERIZED BY THE GFS AND ECMWF
DETERMINISTIC MODELS HAVE EMERGED, WITH GFS DEPICTING SLOW FORWARD
TRACK SPEEDS AND DISSIPATION OF THE CIRCULATION AND ECMWF DEPICTING
ACCELERATION OF THE REMNANT LOW INTO THE MID-LATITUDE WESTERLIES
FOLLOWING THE PERIOD OF SUBTROPICAL TRANSITION. THE CURRENT
FORECAST IS CONSISTENT WITH CONSENSUS GUIDANCE AND PREVIOUS JTWC
FORECASTS, STICKING WITH A SLOW BUT STEADY SOUTHEASTWARD TRACK AND
SUBTROPICAL TRANSITION FOR NOW, WITH THE POSSIBILITY OF MORE RAPID
DISSIPATION IN PLAY.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
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