WDXS32 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10S (SEAN) WARNING NR 
017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.3S 107.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 489 NM SOUTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A NOW
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AS A COMBINATION OF
COLD WATER AND VERTICAL SHEAR DECOUPLES THE VORTEX. DEEP CONVECTION
CONTINUES TO WITHER, WITH CLOUD TOPS NOW UNIVERSALLY WARMER THAN
-60 DEGREES CELSIUS ACROSS THE CIRCULATION, REPRESENTING MOSTLY
REMNANT CIRRUS. THE INITIAL INTENSITY IS SET AT 45 KT BASED ON A
BLEND OF AGENCY DVORAK ESTIMATES AND OBJECTIVE SATELLITE-BASED
INTENSITY ESTIMATES FROM THE UNIVERSITY OF WISCONSIN.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS ADT: 35 KTS AT 212330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 22-23 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: 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 ABOUT 36 HOURS. THE JTWC FORECAST THUS TERMINATES AT 36
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. THE JTWC TRACK FORECAST HAS SHIFTED SLIGHTLY
WESTWARD DUE TO A 25 NM SHIFT WESTWARD IN THE ANALYZED INITIAL
POSITION.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS. DYNAMICAL MODELS EXHIBIT TIGHT CROSS-TRACK
SPREAD, BUT STILL HAVE SIGNIFICANT ALONG-TRACK SPREAD DUE TO
DIFFERENCES IN THE STORM'S FORWARD SPEED. THE JTWC INTENSITY
FORECAST IS ALSO CLOSE TO THE MULTI-MODEL CONSENSUS.

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