Advisories

WDPN32 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.8N 137.6E
   INITIAL INTENSITY: 140 KTS
   GEOGRAPHIC REFERENCE: 319 NM NORTH OF YAP
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 52 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT 
INNER CORE OF DEEP CONVECTION SURROUNDING A 25NM WIDE EYE, WITH EYE 
TEMPERATURES NEAR 20C. THE CONVECTIVE DEPTH AND SYMMETRY OF THE 
EYEWALL HAVE DEGRADED SLIGHTLY OVER THE PAST FEW HOURS IN THE EIR 
DEPICTION, AND CLOUD-TOP TEMPERATURES HAVE WARMED BY 1 TO 2C. 
ANIMATED WATER VAPOR IMAGERY AND ATMOSPHERIC MOTION VECTORS (AMV) 
DEPICT CYCLONIC OUTFLOW UP TO 150MB, EXTENDING RADIALLY OUTWARD FROM 
THE CENTER TO THE EDGE OF THE CENTRAL DENSE OVERCAST (CDO), BEFORE 
TURNING ANTICYCLONICALLY INTO ROBUST POLEWARD AND EQUATORWARD OUTFLOW 
CHANNELS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED 
ON THE WELL-DEFINED 25NM EYE IN THE EIR, SUPPORTED BY A DIRECT 
191203Z ASCAT-B SWATH. THE ASCAT OBSERVATIONS ALSO PROVIDED HIGH-
RESOLUTION WIND DATA TO REFINE THE STRUCTURAL ANALYSIS OF THE SURFACE 
WIND FIELD, WHICH IS NOW ASSESSED WITH HIGH CONFIDENCE. A 190808Z 
SSMIS 91GHZ MICROWAVE IMAGE REVEALED A DISTINCT INNER EYEWALL, A 
WELL-DEFINED MOAT, AND A COHESIVE SECONDARY EYEWALL APPROXIMATELY 
30NM FROM THE CIRCULATION CENTER, PROVIDING DEFINITIVE EVIDENCE OF 
SECONDARY EYEWALL FORMATION (SEF) AND THE IMMINENCE OF AN EYEWALL 
REPLACEMENT CYCLE (ERC). THE INITIAL INTENSITY IS HELD AT 140 KNOTS 
WITH HIGH CONFIDENCE, BASED ON SUBJECTIVE DVORAK CURRENT INTENSITY 
ESTIMATES OF T7.0 AND SUPPORTED BY CIMSS D-PRINT AND SATCON OBJECTIVE 
ESTIMATES. INDEPENDENT OF THE INTERNAL STRUCTURAL DYNAMICS ASSOCIATED 
WITH THE IMMINENT ERC, THE SYNOPTIC ENVIRONMENT REMAINS HIGHLY 
CONDUCIVE FOR DEVELOPMENT, CHARACTERIZED BY LOW VERTICAL WIND SHEAR 
(VWS), ELEVATED SEA SURFACE TEMPERATURES (SSTS), HIGH OCEAN HEAT 
CONTENT (OHC) (EXCEEDING 125 KJ PER CM2), AND STRONG DUAL-CHANNEL 
OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: TRANSITION PERIOD BETWEEN THE WESTERN
FLANK OF A SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST, AND A
BUILDING EXTENSION OF A STR CENTERED IN THE VICINITY OF TAIWAN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   RCTP: T6.5 - 127 KTS
   CIMSS SATCON: 146 KTS AT 190900Z
   CIMSS ADT: 132 KTS AT 191130Z
   CIMSS AIDT: 131 KTS AT 191130Z
   CIMSS D-MINT: 129 KTS AT 191134Z
   CIMSS D-PRINT: 139 KTS AT 191130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG DUAL-CHANNEL
   OTHER FACTORS: EYEWALL REPLACEMENT CYCLE (ERC). 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: SUPER TYPHOON (STY) 29W IS BEGINNING TO 
GRADUALLY ACCELERATE AS IT TRANSITIONS STEERING INFLUENCE FROM THE 
STR TO THE NORTHEAST TO THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE 
STR NEAR TAIWAN, WHICH IS BUILDING EASTWARD SOUTH OF JAPAN. AS THE 
RIDGE TO THE NORTH CONTINUES TO BUILD OVER THE NEXT 12 TO 24 HOURS, 
STY 29W WILL CONTINUE TO ACCELERATE TO 13-14 KNOTS FROM TAU 12 TO TAU 
36. A DEEP MID-LATITUDE TROUGH WILL PROPAGATE ACROSS THE KOREAN 
PENINSULA AROUND TAU 36, INDUCING A BREAK IN THE SUBTROPICAL RIDGE 
AND RESULTING IN THE BIFURCATION OF THE STR INTO TWO DISTINCT RIDGE 
CELLS; ONE SOUTH OF HONSHU AND THE OTHER OVER SOUTHEASTERN CHINA, 
WITH A PRONOUNCED COL REGION OVER THE EAST CHINA SEA (ECS). THE 
PRIMARY SYNOPTIC EVOLUTION EXPECTED AFTER TAU 48 IS THAT THE WESTERN 
RIDGE OVER SOUTHEASTERN CHINA IS FORECAST TO RETROGRADE TOWARD THE 
SINO-VIETNAM BORDER REGION, WHILE THE EASTERN RIDGE SOUTH OF JAPAN 
REMAINS QUASI-STATIONARY. THIS EVOLUTION WILL BROADEN THE BAROMETRIC 
WEAKNESS TO THE NORTH, WHICH WILL BE FURTHER ERODED BY THE PASSAGE OF 
A SERIES OF TRANSIENT SHORTWAVE TROUGHS OVER THE COURSE OF THE 
FORECAST PERIOD. AFTER TAU 48, AS STY 29W APPROACHES THE COL REGION, 
IT WILL DECELERATE TO 7-8 KNOTS DUE TO THE RELAXATION OF THE DEEP-
LAYER STEERING GRADIENT. BY TAU 72, STY 29W WILL INITIATE A POLEWARD 
RECURVATURE INTO THE RIDGE WEAKNESS, ASSISTED BY THE AMPLIFICATION 
AND REORIENTATION OF THE WESTERN PERIPHERY OF THE EASTERN STR INTO A 
MERIDIONAL AXIS. WHILE OVERALL CONFIDENCE IN THE PRIMARY FORECAST 
SCENARIO IS MEDIUM, AN ALTERNATIVE SCENARIO REMAINS PLAUSIBLE, IN 
WHICH STY 29W MAINTAINS A CONTINUOUS NORTHWESTWARD TRAJECTORY 
DIRECTLY INTO TAIWAN. REGARDING INTENSITY, AS THE IMMINENT ERC 
PROGRESSES, STY 29W IS EXPECTED TO WEAKEN BY AT LEAST 10 KNOTS, WITH 
POTENTIAL FOR MORE PRONOUNCED SHORT-TERM DEGRADATION. ASSUMING THE 
ERC COMPLETES WITHIN THE NEXT 12 HOURS, STY 29W SHOULD RE-INTENSIFY 
RAPIDLY, PEAKING AT 145 KNOTS BY TAU 24 AS IT TRAVERSES A POOL OF 
ELEVATED OHC WATERS. HAFS-A AND HWRF BOTH EXPLICITLY DEPICT 
SUBSEQUENT ERC INITIATION SHORTLY AFTER TAU 24; HOWEVER, DUE TO THE 
EXPECTED DECELERATION OF THE SYSTEM AND CONSEQUENT OCEANIC UPWELLING, 
THAT ERC IS UNLIKELY TO COMPLETE. THE COMBINATION OF UPWELLING-
INDUCED SEA SURFACE COOLING AND INCREASING VERTICAL WIND SHEAR WILL 
DRIVE A STEADY WEAKENING TREND THROUGH TAU 96. AS THE SYSTEM RECURVES 
INTO THE ECS, IT WILL ENCOUNTER ENHANCED MID-LATITUDE WESTERLY SHEAR 
AND SYNOPTIC DRY AIR ENTRAINMENT, ACCELERATING THE WEAKENING TREND 
THROUGH THE REMAINDER OF THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN 
STRONG AGREEMENT THROUGH TAU 60, AT WHICH POINT THE SYSTEM REACHES A 
SYNOPTIC INFLECTION POINT. CROSS-TRACK SPREAD IS MINIMAL THROUGH TAU 
36, INCREASING GRADUALLY TO 80NM AT TAU 60. BY TAU 72, THE GFS AND 
GEFS SOLUTIONS DIVERGE SHARPLY WESTWARD, ULTIMATELY TRACKING THE 
SYSTEM THROUGH THE LUZON STRAIT AND JUST SOUTH OF TAIWAN, APPROACHING 
LANDFALL EAST OF HONG KONG BY TAU 120. THE REMAINDER OF THE DYNAMICAL 
MODELS, AS WELL AS THE MULTI-MODEL CONSENSUS MEAN (CONW), REMAIN 
TIGHTLY CLUSTERED ON A NORTHWESTWARD TRAJECTORY, INDICATING LANDFALL 
IN NORTH-CENTRAL TAIWAN SHORTLY AFTER TAU 96 AND EASTERN CHINA BY TAU 
120. CONVERSELY, DATA-DRIVEN MACHINE LEARNING (AI) MODELS DIVERGE 
POLEWARD AT TAU 72, RECURVING THE SYSTEM TO VARYING DEGREES. THE 
OPERATIONAL GOOGLE DEEPMIND (GDM) IS THE MOST AGGRESSIVE RECURVE 
OUTLIER, REACHING THE LATITUDE OF YAKUSHIMA, SOUTHWEST OF KYUSHU, BY 
TAU 120. THE EC-AIFS ENSEMBLE MEAN, DETERMINISTIC EC-AIFS, 
EXPERIMENTAL DEEPMIND, AND THE AI CONSENSUS ARE DISTRIBUTED ALONG A 
SIMILAR TRAJECTORY, SEQUENTIALLY OFFSET TO THE SOUTHWEST. ENSEMBLE 
GUIDANCE CONTINUES TO EXHIBIT EXTREME MEMBER DISPERSION AFTER TAU 72, 
CHARACTERIZED BY A NEARLY 180 DEGREE BIFURCATION AND A ROUGHLY EQUAL 
CLUSTER SPLIT. THE OFFICIAL JTWC FORECAST IS POSITIONED NEAR THE 
MULTI-MODEL CONSENSUS MEAN THROUGH TAU 60, TRANSITIONING TOWARD THE 
AI CONSENSUS FROM TAU 72 TO TAU 120. CONFIDENCE IS LOW IN THE 
EXTENDED RANGE DUE TO THE EXTREME BIFURCATION IN THE DYNAMICAL AND 
ENSEMBLE GUIDANCE. INTENSITY GUIDANCE IS IN GENERALLY GOOD AGREEMENT 
THROUGH THE FORECAST PERIOD. THE JTWC INTENSITY FORECAST DIVERGES 
BELOW GUIDANCE THROUGH TAU 24, AS MOST STATISTICAL-DYNAMICAL MODELS 
DO NOT ADEQUATELY RESOLVE THE NEAR-TERM ERC IMPACTS, BEFORE ALIGNING 
WITH THE UPPER EDGE OF THE GUIDANCE ENVELOPE 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: LOW//
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