Advisories

WDPN32 PGTW 201500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0N 133.0E
   INITIAL INTENSITY: 155 KTS
   GEOGRAPHIC REFERENCE: 639 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 62 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SUPER TYPHOON (STY) 29W MAINTAINS A CIRCULAR, WELL-DEFINED EYE
EMBEDDED IN A NEARLY SYMMETRIC CENTRAL DENSE OVERCAST WITH
EXCELLENT VENTILATION IN ALL DIRECTIONS AND FLARING CONVECTION ON
THE FAR OUTER PERIPHERY OF THE CIRCULATION. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS A 30-NM-WIDE EYE AS WARM
AS +22 DEGREES CELSIUS SURROUNDED BY VERY COLD CLOUD TOP
TEMPERATURES OF -80 TO -83 DEGREES CELSIUS. BD-CURVE-ENHANCED
IMAGERY DEPICTS A SUSTAINED THICK RING OF THE COLD-MEDIUM-GRAY
SHADE AND EVEN SOME COLD-DARK-GRAY SHADES SURROUNDING THE EYE. A
200853Z WSF-M MWI PASS REVEALS A SOLID EYEWALL SURROUNDED BY SPIRAL
RAINBANDS. COINCIDENT SAR PASSES AROUND 200910Z BY RCM-3 AND
SENTINEL-1D DEPICT A NARROW AREA OF LOW EMISSIVITY BETWEEN AN INNER
RING OF EXTREME WINDS AND THE EYEWALL, SUGGESTING THAT THE RADIUS
OF MAXIMUM WINDS IS NEAR 15 NM. THIS STRUCTURE IS CONFINED TO
WITHIN 30 NM OF THE STORM CENTER, IS NOT INDICATIVE OF DOUBLE
EYEWALLS, AND MAY INSTEAD BE INDUCED BY MESOVORTICES WITHIN THE
EYE. STY 29W REMAINS IN A HIGHLY FAVORABLE ENVIRONMENT OF VERY WARM
SEA SURFACE TEMPERATURE (SST) OF 30-31 DEGREES CELSIUS, VERY HIGH
OCEAN HEAT CONTENT OF 150 KJ PER CM2, AND LOW VERTICAL WIND SHEAR
(VWS). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
THE WELL-DEFINED EYE IN SHORTWAVE IR IMAGERY. THE INITIAL INTENSITY
HAS BEEN RAISED TO 155 KTS WITH HIGH CONFIDENCE BASED ON THE
UNANIMOUS T7.5 FROM PGTW, RJTD, AND RCTP. ADT IS ASSESSED TO BE TOO
LOW, WITH THE LARGE EYE SCENE TYPE LIKELY CAPPING THE RAW T-NUMBER
AT 6.5.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE POSITIONED SOUTH OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.5 - 155 KTS
   RJTD: T7.5 - 155 KTS
   RCTP: T7.5 - 155 KTS
   CIMSS SATCON: 139 KTS AT 200600Z
   CIMSS ADT: 129 KTS AT 201200Z
   CIMSS AIDT: 138 KTS AT 201200Z
   CIMSS D-MINT: 154 KTS AT 201142Z
   CIMSS D-PRINT: 150 KTS AT 201200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG RADIAL

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: STY 29W IS MOVING NORTHWESTWARD ALONG THE
SOUTHERN PERIPHERY OF A DEEP-LAYER STR POSITIONED SOUTH OF HONSHU.
BY TAU 24, A SHARP MID-LEVEL TROUGH WILL PASS OVER THE KOREAN
PENINSULA AND APPROACH HONSHU, ERODING THE WESTERN EXTENSION OF THE
STR AND BUILDING THE RIDGE EASTWARD. THIS PATTERN WILL LEAD TO A
WEAKNESS IN THE STR, ALLOWING STY 29W TO TURN POLEWARD. THE SYSTEM
WILL CROSS THE STR AXIS AFTER TAU 72 AND BEGIN TO ACCELERATE
NORTHEASTWARD TOWARD KYUSHU. WITH EYE AND CLOUD-TOP TEMPERATURES
HOLDING STEADY OVER THE PAST FEW HOURS, THE TROPICAL CYCLONE IS
LIKELY AT OR NEAR PEAK INTENSITY. WHILE LOW VWS WILL PREVAIL
THROUGH TAU 72, STY 29W WILL TRAVERSE AN AREA OF MUCH LOWER OHC
NEAR 60 KJ PER CM2 AFTER TAU 24, LEADING TO A WEAKENING TREND. FROM
TAU 60 TO JUST AFTER TAU 72, THE SYSTEM WILL MOVE OVER A PATCH OF
HIGHER OHC NEAR TAIWAN, WHICH WILL BRIEFLY LESSEN THE RATE OF
WEAKENING. STEADY WEAKENING WILL RESUME THEREAFTER DUE TO LOWER OHC
AND INCREASING VWS. BY TAU 120, THE SYSTEM WILL ENTER A STRONGER
BAROCLINIC ENVIRONMENT AND MOVE BENEATH THE SOUTHERN PERIPHERY OF
THE JET STREAM. CONSEQUENTLY, EXTRATROPICAL TRANSITION WILL BEGIN.

MODEL DISCUSSION: A STRONG BIFURCATION IN TRACK GUIDANCE REMAINS
FROM TAU 48 ONWARD, WITH AI MODELS DEPICTING A RECURVATURE SCENARIO
TOWARD KYUSHU AND THE BULK OF THE DYNAMICAL MODELS BRINGING STY 29W
INTO TAIWAN. FOR THE FIRST TIME, HOWEVER, ECMWF, JGSM, THEIR
RESPECTIVE ENSEMBLE MEANS, AND NAVGEM HAVE SHIFTED POLEWARD. EVEN
GFS HAS SHIFTED SLIGHTLY POLEWARD, WHILE JGSM AND NAVGEM NOW DEPICT
A WIDER TURN. THE AI MODELS HAVE CHANGED LITTLE AND CONTINUE TO
DEPICT A LANDFALL OVER KYUSHU. THIS NOTABLE SHIFT INCREASES
CONFIDENCE IN THE RECURVATURE SCENARIO. THE JTWC TRACK FORECAST IS
VERY SIMILAR TO THE PREVIOUS FORECAST. IT ALIGNS WITH THE CORE
CLUSTER OF MODELS THROUGH TAU 48 AND THEN FOLLOWS A BLEND OF THE
AI-MODEL MEAN AND GOOGLE DEEPMIND. THE JTWC FORECAST TRACK IS STILL
NOT AS FAST AS DEEPMIND, WHICH IS 300 NM AHEAD OF THE AI-MODEL MEAN
AND 150 NM AHEAD OF THE JTWC FORECAST POINT AT TAU 120. AS SUCH,
TRACK FORECAST CONFIDENCE IS LOW AFTER TAU 48. A LARGE SPREAD
EXISTS AMONG THE INTENSITY GUIDANCE. ONCE AGAIN, THE SOLUTIONS FROM
HAFS-A, GFS, AND COAMPS-TC ARE DISCOUNTED BECAUSE THEY STILL DEPICT
A TAIWAN LANDFALL SCENARIO. THE JTWC INTENSITY FORECAST LIES AT THE
UPPER END OF THE GUIDANCE ENVELOPE. IT IS CLOSELY ALIGNED WITH THE
DEEPMIND SOLUTION, WHICH DEPICTS GRADUAL TO STEADY WEAKENING AFTER
TAU 12.

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