WDXS32 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10S (SEAN) WARNING NR 
014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.1S 108.4E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 355 NM WEST-SOUTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
WEAKENING SYSTEM, WITH A REMNANT, SMALL INNER-CORE OF DEEP
CONVECTION STARTING TO BE SHEARED TO THE EAST OF THE LOW LEVEL
CIRCULATION CENTER (LLCC). ANIMATED WATER VAPOR IMAGERY SHOWS A
SIGNIFICANT WEDGE OF VERY DRY MID- AND UPPER-LEVEL DRY AIR MOVING
IN FROM THE WEST AND BEGINNING TO PENETRATE TOWARDS THE CORE OF THE
SYSTEM. A 210407Z COWVR COLOR-ENHANCED 37GHZ MICROWAVE IMAGE
REVEALS A RATHER BROAD CIRCULATION CENTER IN THE LOWER LEVELS, WITH
A DEFINED UPPER-LEVEL CIRCULATION CENTER ALIGNED WITH THE ROTATION
SEEN IN THE MSI, DISPLACED ROUGHLY 45NM TO THE EAST-SOUTHEAST. THE
INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN
EXTRAPOLATION OF THE ESTIMATED CENTER SEEN IN THE MICROWAVE IMAGE
NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE, BASED ON A BLEND OF THE AGENCY DVORAK CURRENT INTENSITY
(CI) ESTIMATES, AND THE SATCON ESTIMATE OF 80 KTS. A 210657Z AMSR-2
WIND SPEED PRODUCT SHOWS MAXIMUM WINDS OF 81 KNOTS IN THE
SOUTHEASTERN PORTION OF THE INNER-CORE OF THE SYSTEM. THE
ENVIRONMENT IS BECOMING INCREASINGLY UNFAVORABLE, WITH THE SYSTEM
NOW MOVING ACROSS THE 26C ISOTHERM AND INTO COOLER WATERS, AND
SIGNIFICANT DRY AIR INTRUSION, OFFSETTING THE LOW VWS AND STRONG
POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PORTION OF A SUBTROPICAL RIDGE
(STR) OVER SOUTHWESTERN AUSTRALIA.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T5.0 - 90 KTS
   APRF: T4.5 - 77 KTS
   CIMSS SATCON: 80 KTS AT 210600Z
   CIMSS ADT: 74 KTS AT 210530Z
   CIMSS AIDT: 60 KTS AT 210600Z
   CIMSS D-PRINT: 66 KTS AT 210600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 5-10 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR-MASS ON THE WESTERN PORTION OF
THE CIRCULATION. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 10S WILL CONTINUE TO TRACK ON
SOUTH-SOUTHWESTWARD COURSE FOR THE NEXT 12 HOURS, ALONG THE WESTERN
PERIPHERY OF THE DEEP STR OVER AUSTRALIA. TRACK SPEEDS ARE EXPECTED
TO SLOW STEADILY OVER THE NEXT 24 HOURS AS THE SYSTEM APPROACHES
THE RIDGE AXIS. BY TAU 24, TC 10S WILL BE AT THE RIDGE AXIS AND
BEGIN TO TURN TOWARDS THE SOUTHEAST, ACCELERATING STEADILY AFTER IT
ROUNDS THE RIDGE. IN TERMS OF INTENSITY, THE PRIMARY FACTORS
DRIVING THE CURRENT WEAKENING TREND ARE THE MOVEMENT OVER COOL
WATERS LESS THAN 26C AND THE IMPACT OF SIGNIFICANT DRY AIR
INTRUSION INTO THE CORE OF THE SYSTEM. THE SYSTEM IS EXPECTED TO
CONTINUE WEAKENING AT A PACE OF 15 KNOTS PER 12 HOURS UNTIL
ROUNDING THE RIDGE AXIS. BY THE TIME IT STARTS ITS SOUTHEASTWARD
TRACK, THE SYSTEM WILL LIKELY BE COMPLETELY EXPOSED AND RELATIVELY
SHALLOW, SUCCUMBING TO RAPIDLY INCREASING SHEAR, THE SMOTHERING
EFFECT OF DRY MID-LEVEL AIR AND COOL SSTS. THE PACE OF WEAKENING 
ACTUALLY SLOWS AFTER TAU 24 AS THE REMNANT CIRCULATION SLOWLY LOSES
MOMENTUM AND SPINS DOWN. DISSIPATION BELOW 35 KNOTS IS EXPECTED TO
OCCUR SOMETIME BETWEEN TAU 48 AND TAU 72, THOUGH THE FORECAST IS
EXTENDED TO TAU 72 TO ENSURE CAPTURE OF THE DISSIPATION POINT.
ADDITIONALLY, THE SYSTEM REMAINS NORTH OF THE SUBTROPICAL JET AND
THE BAROCLINC ZONE UNTIL ABOUT TAU 60 WHERE IT WILL BEGIN TO TAKE
ON MORE EXTRATROPICAL FEATURES. TRANSITION TO A SUBTROPICAL, THEN
EXTRATROPICAL LOW WILL BE OCCURRING SIMULTANEOUSLY WITH
DISSIPATION, AND THE CURRENT FORECAST CALLS FOR THE SYSTEM TO
DISSIPATE PRIOR TO THIS TRANSITION PHASE. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN STRONG
CROSS-TRACK AGREEMENT THROUGH THE FORECAST PERIOD. HOWEVER,
ALONG-TRACK UNCERTAINTY INCREASES AFTER TAU 24 WHEN THE SYSTEM
CROSSES THE RIDGE AXIS. THE ECMWF AND NAVGEM ARE THE FASTEST
MODELS, WHILE GFS AND GEFS ARE THE SLOWEST, LAGGING ABOUT 100NM
BEHIND THE FAST MODELS AT TAU 72. THE JTWC FORECAST IS CONSISTENT
WITH THE PREVIOUS FORECAST AND INLAID CLOSE TO THE CONSENSUS MEAN
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN RELATIVELY GOOD
AGREEMENT, WITH ALL CONSENSUS MEMBERS INDICATING STEADY TO RAPID
WEAKENING THROUGH TAU 36, FOLLOWED BY A MORE GRADUAL WEAKENING
THEREAFTER DEPICTED BY THE MAJORITY OF THE MESOSCALE MODELS. THE
JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN, BRACKETED BY THE
HWRF AND HAFS-A, WITH HIGH CONFIDENCE.   

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