Advisories

WDPN32 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 29W (CHAMPI) WARNING NR 033//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.2N 124.9E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 356 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY
LARGE TYPHOON (TY), EXHIBITING A RAPIDLY SHRINKING EYE, A DEGRADING 
INNER EYEWALL, AND A NASCENT SECONDARY EYEWALL. A 220955Z WSF-M 
COLOR-ENHANCED 89GHZ MICROWAVE IMAGE DEPICTED A CONCENTRIC EYEWALL 
FORMATION. THE INNER EYEWALL IS STRONGEST ON THE EASTERN FLANK AND 
OPEN IN THE SOUTHWESTERN QUADRANT. BEYOND THE DISTINCT MOAT FEATURE, 
THE SECONDARY EYEWALL PERSISTS AT ABOUT DOUBLE THE RADIAL DISTANCE OF 
THE INNER EYEWALL, AND IS LIKEWISE STRONGEST ON THE EASTERN FLANK AND 
FRAGMENTED IN THE SOUTHWESTERN QUADRANT. DUE TO ITS DECELERATING 
TRANSLATIONAL SPEED, TY 29W IS UPWELLING SIGNIFICANTLY COOLER WATER 
TO THE OCEAN SURFACE, INHIBITING THE AIR-SEA FLUXES NEEDED FOR THE 
ERC TO PROGRESS, RESULTING IN A STALLED CONCENTRIC EYEWALL FORMATION. 
THE SYSTEM HAS ALSO EXHIBITED PRONOUNCED TROCHOIDAL MOTION OVER THE 
PAST SIX HOURS AS IT MOVES INTO A WEAKER STEERING ENVIRONMENT AND 
CONVECTIVE FORCING IS DISRUPTED BY THE STALLED ERC. THE INITIAL 
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN 
THE EIR. TWO COINCIDENT SYNTHETIC APERTURE RADAR (SAR) PASSES; AN 
RCM-3 AT 220937Z AND A SENTINEL-1C AT 220943Z, DEPICTED A RAPIDLY 
WEAKENING SYSTEM, WITH AN ESTIMATED MEAN VMAX OF 85-95 KNOTS, THOUGH 
ISOLATED HIGHER WINDSPEEDS WERE OBSERVED IN THE RAW DATA. THE INITIAL 
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, SET AT 100 KNOTS, 
CONSISTENT WITH THE SAR DATA AND THE CIMSS ADT AND D-MINT ESTIMATES. 
ENVIRONMENTAL CONDITIONS ARE MARGINAL. THOUGH VERTICAL WIND SHEAR IS 
LOW AND OUTFLOW ALOFT IS VERY STRONG, SSTS ARE RELATIVELY COOL, WHICH 
ALONG WITH THE STALLED ERC, IS RESULTING IN A PRONOUNCED WEAKENING 
TREND.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH OF HONSHU. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS ADT: 99 KTS AT 221140Z
   CIMSS AIDT: 93 KTS AT 221140Z
   CIMSS D-MINT: 100 KTS AT 220958Z
   CIMSS D-PRINT: 97 KTS AT 221200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: EYEWALL REPLACEMENT CYCLE (ERC); OCEANIC
UPWELLING.  

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 29W IS CURRENTLY MOVING SLOWLY IN A
TROCHOIDAL FASHION AS IT MOVES INTO A WEAK STEERING PATTERN, DUE
SOUTH OF A LARGE COL IN THE DEEP-LAYER STEERING PATTERN. THE 
TROCHOIDAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 12 TO 24 HOURS 
AS THE SYSTEM DRIFTS DEEPER INTO THE COL REGION AND THE ERC REMAINS 
STALLED. HOWEVER, THE MEAN MOTION VECTOR WILL REMAIN TOWARD THE 
NORTHWEST, INDEPENDENT OF THE SHORT-TERM ERRATIC, TROCHOIDAL MOTIONS. 
THE SYSTEM WILL MAINTAIN A 6-8 KNOT SPEED OF ADVANCE OVER THE NEXT 12 
TO 24 HOURS AS IT NEARS THE AXIS OF THE STR TO THE EAST. THE FORECAST 
KEEPS THE CORE OF TY 29W OFFSHORE OF THE NORTHEAST TIP OF TAIWAN AS 
IT BEGINS RECURVATURE. AFTER TAU 24, TY 29W WILL TURN NORTHEASTWARD 
AND ACCELERATE ALONG THE NORTHWESTERN FLANK OF THE STR SOUTH OF 
JAPAN, MOVE INTO THE CENTRAL PORTION OF THE EAST CHINA SEA (ECS), AND 
MAKE LANDFALL ALONG THE SOUTHWESTERN COAST OF KYUSHU AROUND TAU 72. 
THE SYSTEM WILL THEN QUICKLY CROSS THE SOUTHERN PORTION OF KYUSHU AND 
REEMERGE OVER WATER, TRACKING SOUTH OF SHIKOKU THROUGH THE REMAINDER 
OF THE FORECAST PERIOD. REGARDING INTENSITY, TY 29W WILL CONTINUE TO 
WEAKEN OVER THE NEXT 12 HOURS DUE TO THE REASONS OUTLINED PREVIOUSLY. 
HOWEVER, IT WILL SOON MOVE OVER A REGION OF HIGH OCEAN HEAT CONTENT 
(OHC) WHICH LIES TO THE SOUTH AND SOUTHWEST OF ISHIGAKIJIMA. AS THE 
SYSTEM PASSES OVER THIS REGION, THE WEAKENING TREND WILL BE BRIEFLY 
ARRESTED, AND TY 29W WILL MAINTAIN 90 KNOTS INTENSITY FROM TAU 12 TO 
TAU 24. AFTER PASSING THROUGH THE SOUTHERN RYUKYUS, TY 29W WILL BEGIN 
TO QUICKLY WEAKEN AS IT MOVES OVER COOLER WATERS AND ENCOUNTERS 
INCREASING SHEAR AND ENTRAINMENT OF DRY MID-LEVEL AIR FROM THE WEST. 
AFTER TAU 36, THE SYSTEM WILL WEAKEN MORE RAPIDLY AS SHEAR INCREASES 
SHARPLY AND TY 29W BECOMES ENVELOPED IN DRY AIR. BY TAU 60, TY 29W 
BEGINS EXTRATROPICAL TRANSITION (ETT) AS IT PHASES WITH A 500MB 
SHORTWAVE TROUGH. ASSUMING THE SYSTEM DOES NOT DISSIPATE PRIOR TO TAU 
72, WHICH REMAINS A DISTINCT POSSIBILITY, IT IS FORECAST TO COMPLETE 
ETT BETWEEN TAU 72 AND TAU 96.  

MODEL DISCUSSION: THE BULK OF THE TRACK GUIDANCE HAS CONTINUED TO 
COME INTO BETTER AGREEMENT WITH EACH SUCCESSIVE MODEL RUN. HOWEVER, 
WITH THIS RUN, DYNAMICAL MODELS ECMWF, NAVGEM, AND GALWEM HAVE 
DEVIATED FROM THE REMAINDER OF THE MODEL PACKAGE AND NOW DEPICT TY 
29W TRACKING STRAIGHT NORTH-NORTHWESTWARD, MAKING LANDFALL ALONG THE 
NORTHERN TIP OF TAIWAN AND THEN DISSIPATING ALONG THE EASTERN CHINESE 
COAST BY TAU 96. THIS IS A SIGNIFICANT DEPARTURE FROM THE 06Z MODEL 
RUN, IN WHICH EACH OF THESE MODELS DEPICTED TY 29W RECURVING AND 
REACHING KYUSHU OR SOUTH KOREA BEFORE DISSIPATING. THE GFS, GEFS, 
ECEPS, AND THE CONSENSUS MEAN HAVE SHIFTED CLOSER TO THE AI MODELS, 
WHICH THEMSELVES HAVE REMAINED VERY CONSISTENT ON THE TRAJECTORY OF 
THE RECURVE FOR THE LAST SEVERAL DAYS. THE MAIN CONCERN CONTINUES TO 
BE THE SPEED OF ADVANCE AFTER RECURVATURE AND THE TIMING OF 
DISSIPATION. THE OPERATIONAL AND EXPERIMENTAL DEEPMIND MODELS ARE THE 
SLOWEST OF THE ENTIRE PACKAGE AND DISSIPATE THE SYSTEM SHORT OF 
KYUSHU. MEANWHILE, THE GFS, GEFS MEAN, AND AI CONSENSUS (AICN) ARE 
THE FASTEST OF THE MODELS, WITH THE FORMER REACHING SHIKOKU BY TAU 96 
AND THE LATTER ADVANCING TO A POINT SOUTHEAST OF KYOTO. THE JTWC 
FORECAST IS POSITIONED JUST WEST OF THE AICN THROUGH TAU 36, THEN 
FOLLOWS THE AICN THROUGH TAU 96. INTENSITY GUIDANCE IS IN GOOD 
AGREEMENT OVERALL, THOUGH ONLY HAFS-A AND HWRF DEPICT THE ARRESTED 
WEAKENING THROUGH TAU 24. THE JTWC FORECAST IS PLACED NEAR THE HWRF 
THROUGH TAU 24, THEN CLOSE TO THE MULTI-MODEL CONSENSUS MEAN THROUGH 
THE REMAINDER OF THE FORECAST. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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