Advisories

WDPN32 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.3N 138.4E
   INITIAL INTENSITY: 140 KTS
   GEOGRAPHIC REFERENCE: 289 NM NORTH OF YAP
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 53 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN IMPRESSIVE 
SYSTEM, WITH A SYMMETRICAL, 25NM WIDE EYE, A PRONOUNCED STADIUM 
EFFECT AND MULTIPLE MESOVORTICES ROTATING AROUND INNER EDGE OF THE 
EYEWALL. EYE TEMPERATURES ARE SOME OF THE HIGHEST SEEN WITH THIS 
STORM, APPROACHING 21C AT 0600Z. A 190232Z AMSR3 89GHZ MICROWAVE 
IMAGE REVEALED A SOLID INNER EYEWALL OF VERY STRONG CONVECTION, 
AND A SECONDARY EYEWALL WHICH WRAPS FROM THE EASTERN SIDE OF THE EYE, 
COUNTER-CLOCKWISE AROUND THE EYE, CONNECTING TO THE INNER EYEWALL 
IN THE SOUTHERN QUADRANT AND A LARGER STATIONARY BANDING COMPLEX 
(SBC) POSITIONED APPROXIMATELY 100NM OUT FROM THE CENTER IN THE EAST 
AND SOUTHEASTERN SECTORS. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE EYE IN THE MSI. THE INITIAL MOTION VECTOR IS 
285 AT 8 KTS, WITH A PRONOUNCED TROCHOIDAL MOTION EVIDENT IN THE 
ANIMATED MSI. THE SLOWDOWN IS DUE TO THE DEVELOPING WEAKNESS IN THE 
RIDGE TO THE NORTH WHILE THE WOBBLING IS LIKELY A RESPONSE TO SEF. 
THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED 
HIGHER THAN THE BULK OF THE OBJECTIVE ESTIMATES IN LIGHT OF THE 
T7.0 DVORAK ESTIMATES FROM BOTH PGTW AND RJTD. UPPER-LEVEL ATMOSPHERIC 
MOTION VECTORS (AMVS) DEPICT STRONG CYCLONIC OUTFLOW UP TO 150MB, 
WHICH THEN TURNS ANTICYCLONICALLY BOTH POLEWARD AND EQUATORWARD, 
PROVIDING ROBUST DUAL-CHANNEL OUTFLOW. SSTS ARE VERY WARM (30-31C) 
AND THE SYSTEM IS APPROACHING A POOL OF OCEANIC WATERS WITH THE 
HIGHEST OHC (150 KJ PER CM2) IN THE ENTIRE BASIN. CONDITIONS ARE NEAR 
OPTIMAL FOR ADDITIONAL INTENSIFICATION, THE ONLY LIMITING FACTOR BEING 
THE HIGH PROBABILITY OF ADDITIONAL EYEWALL REPLACEMENT CYCLES (ERC).

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: IN AGGREGATE, THE SYSTEM IS TRACKING ALONG 
THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO 
THE NORTHEAST. HOWEVER, A SIGNIFICANT WEAKNESS HAS DEVELOPED IN THE 
RIDGING PATTERN TO THE NORTH, RESULTING IN A SHARP DECELERATION OVER 
THE PAST SIX HOURS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   CIMSS SATCON: 122 KTS AT 190640Z
   CIMSS ADT: 134 KTS AT 190540Z
   CIMSS AIDT: 134 KTS AT 190540Z
   CIMSS D-MINT: 131 KTS AT 190352Z
   CIMSS D-PRINT: 143 KTS AT 190540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG DUAL-CHANNEL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: SUPER TYPHOON (STY) 29W HAS SLOWED DOWN AND
EXHIBITED A TROCHOIDAL WOBBLE OVER THE PAST SIX HOURS, IN RESPONSE
TO BOTH SEF AND A WEAKNESS IN THE STEERING RIDGE TO THE NORTH. THE
ECMWF AND EC-AIFS APPEAR TO HAVE INITIALIZED THE SYNOPTIC STEERING
SETUP BETTER THAN GFS, AND DEPICTS A LARGE STR EAST-NORTHEAST OF
29W, A COL TO THE NORTH, AND A SECOND STR CENTERED NEAR HONG KONG
EXTENDING NORTHEASTWARD TO SOUTH OF HONSHU. OVER THE NEXT 12 TO 18
HOURS, THE RIDGE TO THE NORTHEAST WILL SLIDE SOUTHWARD WHILE THE
RIDGE OVER EASTERN CHINA BUILDS EASTWARD, ELIMINATING THE COL
REGION TO THE NORTH. 29W WILL ACCELERATE NORTHWESTWARD AFTER TAU 
12, INCREASING SPEED TO 13 KNOTS THROUGH TAU 48. BY TAU 48, AN 
APPROACHING MID-LATITUDE TROUGH WILL SPLIT THE RIDGING PATTERN, 
WITH A RIDGE CENTER DEVELOPING SOUTH OF TOKYO AND A SECOND RIDGE 
CENTER DEVELOPING OVER SOUTHEASTERN CHINA, AND A PRONOUNCED COL 
DEVELOPING OVER THE EAST CHINA SEA. A SERIES OF SHORTWAVE TROUGHS 
WILL PASS BY TO THE NORTH, HELPING TO MAINTAIN THE COL REGION OVER 
THE ECS THROUGH THE END OF THE FORECAST. 29W WILL BEGIN DECELERATING 
AFTER TAU 48 AS THE STEERING GRADIENT RELAXES AS THE SYSTEM MOVES 
SOUTH OF THE COL REGION. BY TAU 96, 29W WILL BEGIN TO RECURVE INTO 
THE WEAKNESS IN THE RIDGE, PASSING NORTHEAST OF NORTHERN TAIWAN AND 
MOVING INTO THE SOUTHERN PORTION OF THE ECS BY TAU 120. AN ALTERNATE 
SCENARIO SEES MINIMAL INFLUENCE OF THE COL REGION ON 29W, AND THE 
SYSTEM MAINTAINS A STRAIGHT NORTHWESTWARD TRAJECTORY THROUGH TAU 120, 
MAKING LANDFALL ALONG THE EAST COAST OF TAIWAN AFTER TAU 96. CURRENT 
MODEL PROJECTIONS DEPICT A SIGNIFICANT BIFURCATION, WITH A VERY WIDE 
DISPERSION ACROSS A VAST EXPANSE OF THE WESTERN PACIFIC. REGARDING 
INTENSITY, THE SYSTEM IS IN AN OPTIMAL ENVIRONMENT FOR ADDITIONAL 
INTENSIFICATION. HOWEVER, THE UNCERTAINTY IN THE ONSET TIMING, AND 
DURATION OF LIKELY ERCS, MEANS THAT LARGE DEVIATIONS BOTH ABOVE AND 
BELOW THE FORECAST INTENSITY TREND ARE LIKELY. AFTER TAU 48, AS THE 
SYSTEM SLOWS, IT WILL BE IMPACTED BY SELF-INDUCED OCEANIC UPWELLING, 
AND MARGINALLY HIGHER VWS, WEAKENING STEADILY FROM TAU 60 TO TAU 120. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT UP TO TAU
60. CROSS-TRACK SPREAD AT TAU 60 IS 95NM BETWEEN THE UKMET ENSEMBLE
MEAN AND GFS ON THE SOUTHERN EXTENT OF THE ENVELOPE AND THE EC-AIFS
ENSEMBLE MEAN ON THE NORTHERN EDGE. BEYOND TAU 60, THE MODEL
PACKAGE DIVERGES SHARPLY, WITH THE AI-MODELS ALL SEPARATING FROM
THE PHYSICS-BASED MODELS TO VARYING DEGREES AS EARLY AS TAU 72. THE
EC-AIFS ENSEMBLE IS THE MOST AGGRESSIVELY RECURVING MODEL, THE
OPERATIONAL DEEPMIND IS NEXT, FOLLOWED BY A GROUPING CONSISTING OF
THE EXPERIMENTAL DEEPMIND, WINDBORNE MODEL, EC-AIFS AND THE AI
CONSENSUS MEAN WHICH ALL RECURVE THE SYSTEM TO A POSITION NORTHEAST
OF TAIPEI BY TAU 120. THE PHYSICS MODELS ARE ALL CONSTRAINED TO A
NORTHWESTWARD TRAJECTORY IN AN ENVELOPE FROM THE SOUTHERN TIP OF
TAIWAN (GFS) AND JUST SOUTH OF TAIPEI (NAVGEM). ENSEMBLE TRACKERS
AT TAU 120 ARE WIDELY DISPERSED, FROM EAST OF TAIWAN TO SOUTHWEST
OF SASEBO. THE JTWC FORECAST IS POSITIONED NEAR THE AI CONSENSUS
AND AMONGST THE TIGHT AI-BASED MODEL GROUPING FROM TAU 72 TO TAU
120, WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL INTENSIFY THROUGH TAU 24 THEN GRADUALLY AND
STEADILY WEAKEN THROUGH THE REMAINDER OF THE FORECAST. HAFS-A IS
THE MOST AGGRESSIVE, DEPICTING A PEAK INTENSITY OF 155 KNOTS AT TAU
24, WHILE THE REMAINDER OF THE GUIDANCE PEAKS THE SYSTEM AT AROUND
145 KNOTS. THE JTWC FORECAST IS PLACED CLOSE TO THE HAFS-A THROUGH
THE FORECAST PERIOD. 

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