Advisories

WDPN32 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 29W (CHAMPI) WARNING NR 034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.9N 124.3E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 336 NM SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 42 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 29W AS A STILL VERY LARGE CYCLONE WITH EXPANSIVE SYMMETRIC
RADIAL BANDING. THE EYE HAS EXPANDED OVER THE PAST 6 HOURS AS THE
RESULT OF WHAT IS LIKELY A FAILED EYEWALL REPLACEMENT CYCLE. A
221639Z GMI 89 GHZ MICROWAVE IMAGE REVEALED THAT THE CONCENTRIC
EYEWALL CONFIGURATION PREVIOUSLY OBSERVED IS NO LONGER A DEFINED
FEATURE. THE REMAINING INNER EYEWALL STRUCTURE HAS REMAINED AND
EXPANDED TO ABOUT 25 NM IN DIAMETER. THE EIR ALSO SHOWS WARMING
CLOUD TOPS IN THE INNER CORE CONVECTION AND THROUGHOUT THE
CONVECTIVE BANDING. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE EYE IN EIR IMAGERY. THE INITIAL INTENSITY
OF 95 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS
OF THE T5.5 AGENCY DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY
ESTIMATES. THE ENVIRONMENT IS CHARACTERIZED AS MARGINAL WITH LOW
VERTICAL WIND SHEAR (VWS) AND EXCELLENT OUTFLOW BEING OFFSET BY
COOLER SEA SURFACE TEMPERATURES, LOWER OCEAN HEAT CONTENT, AND COLD
WATER UPWELLING.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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 SATCON: 106 KTS AT 221706Z
   CIMSS ADT: 90 KTS AT 221730Z
   CIMSS AIDT: 82 KTS AT 221730Z
   CIMSS D-MINT: 96 KTS AT 221427Z
   CIMSS D-PRINT: 92 KTS AT 221730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: COLD WATER UPWELLING

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE LATEST FORECAST TRACK SPEED HAS
SLOWED CONSIDERABLY AFTER TAU 24. 

FORECAST DISCUSSION: TY 29W (CHAMPI) HAS CONTINUED NORTHWESTWARD
OVER THE PAST 6 HOURS AS IT APPROACHES THE AXIS OF THE STEERING
RIDGE CENTERED TO THE NORTHEAST. THE TRACK IS FORECAST TO CONTINUE
GENERALLY NORTHWESTWARD OVER THE NEXT 24 HOURS, BRINGING THE CENTER
JUST EAST OF TAIPEI AT TAU 24.FROM TAU 24 TO 48 THE TRACK TURNS
NORTH-NORTHEASTWARD AS THE SYSTEM ROUNDS THE RIDGE AXIS. THE TRACK
SPEED IS EXPECTED TO BE SLOWER THAN PREVIOUS FORECASTS THROUGH THE
FIRST 48 HOURS AS THE SYSTEM MAKES THE POLEWARD AND EASTWARD TURN.
AFTER TAU 48, THE TRAJECTORY TURNS TO AN EAST-NORTHEASTWARD TURN ON
APPROACH TO KYUSHU, MAKING LANDFALL SOUTH OF SASEBO JUST AFTER TAU
72. THE TRACK IS THEN EXPECTED TO ACCELERATE EASTWARD OFFSHORE OF
SOUTHERN HONSHU WITHIN THE MIDLATITUDE BAROCLINIC ZONE. THE
INTENSITY OF TY 29W IS FORECAST TO STEADILY DECREASE THROUGH TAU 60
IN AN ENVIRONMENT OF INCREASING VWS AND COOLING SEA SURFACE
TEMPERATURES. EXTRATROPICAL TRANSITION (ETT) IS EXPECTED TO BEGIN
BETWEEN TAU 60 AND 72, BECOMING EXTRATROPICAL BY TAU 72. AS A
RESULT OF THE STEADY WEAKENING AND ETT, THE INTENSITY AS IT MAKES
LANDFALL OVER KYUSHU IS PROJECTED TO BE 30-35 KTS.

MODEL DISCUSSION: MODEL TRACK GUIDANCE HAS COLLAPSED TO GOOD
AGREEMENT ON THE RECURVING SCENARIO, WITH PHYSICS-BASED AND AI
MODELS NO LONGER BIFURCATING AS NOTED IN PREVIOUS FORECASTS.
HOWEVER, THE ALONG-TRACK SPREAD VARIES SIGNIFICANTLY AS MOST OF THE
AI MODELS, WITH THE NOTABLE EXCEPTION OF GOOGLE DEEPMIND,
ACCELERATE INTO THE MIDLATITUDES MUCH FASTER THAN THE PHYSICS-BASED
MODELS. THE RESULT OF THIS DISCREPANCY IN TRACK SPEEDS IS THAT THE
AI CONSENSUS IS HEAVILY BIASED TOWARD A MUCH FASTER TRACK SPEED.
THE JTWC TRACK IS HEDGED SLOWER THAN THE AI CONSENSUS AND CLOSER TO
THE TRADITIONAL CONSENSUS AND GOOGLE DEEPMIND GROUPING. REGARDLESS
OF THE DISCREPANCY IN TRACK SPEEDS, THE INTENSITY GUIDANCE IS IN
GOOD AGREEMENT ABOUT THE WEAKENING TREND THROUGHOUT THE FORECAST
PERIOD.

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