WDXS32 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10S (SEAN) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.8S 107.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 450 NM SOUTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
DECAYING VORTEX OVER COLDER SEA SURFACE TEMPERATURES OF 24 TO 25
DEGREES CELSIUS. DEEP CONVECTION IS DECREASING IN COVERAGE, AND THE
VORTEX IS TILTED A BIT SOUTHWARD WITH HEIGHT. THE PRECISE LOW-LEVEL
CIRCULATION CENTER (LLCC) IS A BIT DIFFICULT TO LOCATE DUE TO THE
REMAINING CENTRAL DENSE OVERCAST, BUT IT APPEARS TO BE NEAR THE
NORTHERN EDGE OF THE CONVECTIVE CANOPY. HEALTHY POLEWARD
UPPER-LEVEL OUTFLOW IS OBSERVED INTO A JET STREAK ENTRANCE REGION
TO THE SOUTH OF THE CYCLONE. THE INITIAL INTENSITY IS SET AT 55 KT
BASED ON A BLEND OF AGENCY DVORAK INTENSITY ESTIMATES AND A 1453Z
ASCAT-C SCATTEROMETER PASS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER AVERAGED SUBTROPICAL RIDGE
OVER WESTERN AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   APRF: T4.0 - 65 KTS
   CIMSS SATCON: 63 KTS AT 211603Z
   CIMSS ADT: 57 KTS AT 211450Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 24-25 CELSIUS
   OUTFLOW: MODERATE 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: TROPICAL CYCLONE 10S (SEAN) IS IN ITS TERMINAL
DECAY PHASE AS IT MOVES OVER COLDER WATERS TOWARD THE SUBTROPICAL
JET STREAM. A STRONG ENVIRONMENTAL PRESSURE GRADIENT WILL MAINTAIN
AN EXPANSIVE AREA OF STIFF WINDS ON THE SOUTHERN AND WESTERN SIDES
OF THE CYCLONE FOR THE NEXT 3 DAYS, BUT NUMERICAL MODELS ARE IN
GOOD AGREEMENT THAT SEAN WILL WEAKEN BELOW WARNING THRESHOLD (35
KT) WITHIN 48 HOURS. THE JTWC FORECAST THUS TERMINATES AT 48 HOURS
WHEN THE CYCLONE DISSIPATES. A GRADUAL BEND IN SEAN'S TRACK
SOUTHWARD AND THEN SOUTHEASTWARD WILL OCCUR AS THE CYCLONE ROUNDS
THE WESTERN PERIPHERY OF THE DEEP-LAYER SUBTROPICAL RIDGE OVER
WESTERN AUSTRALIA.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO BUT SLIGHTLY
FASTER THAN THE MULTI-MODEL CONSENSUS, STICKING CLOSE TO A BLEND OF
THE ECMWF, ECMWF ENSEMBLE MEAN, GFS, AND GFS ENSEMBLE MEAN. MODEL
CROSS-TRACK SPREAD IS TIGHT, BUT THERE IS A SIGNIFICANT AMOUNT OF
ALONG-TRACK SPREAD IN THE SHORT TERM. THE JTWC FORECAST TRACK IS
20-30 NM EAST OF THE PREVIOUS FORECAST. THE JTWC INTENSITY FORECAST
IS CLOSE TO THE MULTI-MODEL CONSENSUS.

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