WDXS32 PGTW 211500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10S (SEAN) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.3S 107.5E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 433 NM SOUTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 10S (SEAN) CONTINUES TO STEADILY DETERIORATE
AS IT APPROACHES THE SUBTROPICAL RIDGE (STR) AXIS FAR WEST OF SHARK
BAY, AUSTRALIA. ANIMATED PROXY VISIBLE (PROXYVIS) SATELLITE IMAGERY
DEPICTS A VERY SMALL AREA OF SHALLOW CONVECTION AND REMNANT CIRRUS
DEBRIS OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). THE
PROXYVIS ALSO SHOWS SHALLOW BANDS OF STRATOCUMULUS CLOUDS IN
WELL-DEFINED LOW-LEVEL BANDS ALL ALONG THE WESTERN HEMISPHERE OF
THE CIRCULATION. A 211131 WSF-M COLOR-ENHANCED 89GHZ MICROWAVE
IMAGE DEPICTS WELL-DEFINED, SHALLOW BANDING FEATURES WRAPPING INTO
A COMPACT LOW LEVEL CIRCULATION CENTER AND ALL CONVECTION DISPLACED
SOUTHEAST OF THE CENTER. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE USING EXTRAPOLATION OF THE AFOREMENTIONED MICROWAVE
IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON A BLEND OF AGENCY DVORAK CURRENT INTENSITY (CI) ESTIMATES
AND THE OBJECTIVE INTENSITY ESTIMATES NOTED ABOVE. THE ENVIRONMENT
CONTINUES TO DETERIORATE. CIMSS DEEP-LAYER SHEAR IS ESTIMATED AS
FROM THE NORTH AT JUST FIVE KNOTS THOUGH GFS AND ECMWF
MODEL-DERIVED SOUNDINGS TELL A SLIGHTLY DIFFERENT TALE, WITH
DEEP-LAYER SHEAR EXCEEDING 15 KNOTS FROM THE WEST AND MID-LEVEL
SHEAR PUSHING 25 KNOTS. THE DEPICTION IN THE MICROWAVE IMAGERY
STRONGLY SUGGESTS THE MODEL-DERIVED SHEAR ESTIMATES ARE MORE
CORRECT IN THIS CASE. SSTS ARE NOW WELL-BELOW 26C AS WELL, WITH
THESE NEGATIVE FACTORS OFFSETTING THE ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED OVER 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 ADT: 59 KTS AT 211130Z
   CIMSS AIDT: 56 KTS AT 211200Z
   CIMSS D-MINT: 51 KTS AT 211124Z
   CIMSS D-PRINT: 55 KTS AT 211230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 23-24 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR INTRUSION IN THE MID- AND UPPER-LEVELS. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 HAS YET TO REACH THE STR AXIS, AS THE
TRACK CONTINUES TOWARDS THE SOUTHWEST, THOUGH THERE ARE SOME SIGNS
IN THE MOST RECENT FRAMES OF PROXYVIS IMAGERY THAT THE SYSTEM IS
STARTING TO SLOW DOWN PRECIPITOUSLY, A SIGN THAT IT IS REACHING THE
RIDGE AXIS IMMINENTLY. REGARDLESS, IT IS ANTICIPATED THAT TC 10S
WILL CONTINUE TO SLOW DOWN OVER THE NEXT 12 HOURS AS IT REACHES AND
THEN ROUNDS THE RIDGE AXIS. BY TAU 24, THE SYSTEM SHOULD BE SOUTH
OF THE AXIS AND WILL BEGIN TO ACCELERATE TOWARDS THE SOUTHEAST
THROUGH THE REMAINDER OF THE FORECAST PERIOD. NOW THAT THE SYSTEM
HAS MOVED OVER 23C OR EVEN COOLER WATERS, THE SYSTEM HAS LOST ITS
ENERGY SOURCE, AND THIS IS REFLECTED IN THE FACT THAT CONVECTIVE
ACTIVITY HAS COMPLETELY COLLAPSED OVER THE LAST FEW HOURS.
ADDITIONALLY, THE INFLUX OF VERY DRY AIR IN THE UPPER- TO
MID-LEVELS OF THE ATMOSPHERE MOVING IN FROM THE WEST HAS STARTED TO
SMOTHER THE SYSTEM FROM ABOVE, WHILE MODERATE TO STRONG WESTERLY
SHEAR IS TEARING THE VORTEX APART. ALL THINGS CONSIDERED; THE
SYSTEM WILL LIKELY BE A REMNANT LOW-LEVEL VORTEX WITHIN THE NEXT 12
TO 24 HOURS, RAPIDLY TAKING ON A MORE SUBTROPICAL LOOK AS IT
CONTINUES POLEWARD. THE SYSTEM IS EXPECTED TO RAPIDLY WEAKEN OVER
THE NEXT 24 HOURS AS IT ROUNDS THE RIDGE, BUT THEN THE PACE OF
WEAKENING WILL SLOW AS THE REMNANT VORTEX SLOWLY SPINS DOWN. THE
SYSTEM IS EXPECTED TO DISSIPATE BELOW WARNING CRITERIA NO LATER THAN
TAU 48 WHILE SIMULTANEOUSLY UNDERGOING EXTRATROPICAL TRANSITION. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD
CROSS-TRACK AGREEMENT, WITH MINIMAL CROSS-TRACK SPREAD AMONGST THE
CONSENSUS MEMBERS. ALONG-TRACK SPREAD IS STILL PRESENT BUT MUCH
LOWER THAN IN THE PREVIOUS RUN. THE JTWC FORECAST IS LAID CLOSE TO
THE MULTI-MODEL CONSENSUS MEAN WITH HIGH CONFIDENCE. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT, WITH ALL AVAILABLE GUIDANCE SHOWING
RAPID WEAKENING THROUGH TAU 24, THEN A SLOWER PACE OF WEAKENING
THROUGH THE END OF THE FORECAST PERIOD. THE JTWC FORECAST CLOSELY
TRACES THE CONSENSUS MEAN THROUGH THE FORECAST WITH HIGH
CONFIDENCE.  

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