Advisories

WDPN32 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
030//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.9N 126.9E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 399 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 52 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SUPER
TYPHOON (STY) 29W (CHAMPI) AS AN EXPANSIVE SYSTEM WITH A LARGE EYE, 
MEASURING 33 NM IN DIAMETER, WITH A TEMPERATURE OF 18 C. THE 
SURROUNDING COLDEST CLOUD TOPS HAVE WARMED SLIGHTLY OVER THE PAST SIX 
HOURS, PARTICULARLY ON THE WESTERN FLANK. THIS ALIGNS WITH A 211721Z 
GPM MICROWAVE SUITE WHICH REVEALS THE INNER EYEWALL HAS BECOME ERODED 
IN THE SOUTHWESTERN QUADRANT WHILE THE SECONDARY EYEWALL -- SEPARATED 
BY A 35 NM MOAT -- HAS STRENGTHENED ON THE SOUTHERN SEMICIRCLE, 
INDICATING THE LIKELY ONSET OF ANOTHER EYEWALL REPLACEMENT CYCLE 
(ERC). HOWEVER, DUE TO THE OVERALL EXPECTED CONTINUED WEAKENING OF THE 
SYSTEM MOVING FORWARD, IT IS POSSIBLE THAT THE ERC DOES NOT COMPLETE, 
AS THE SECONDARY EYEWALL IN THE AFOREMENTIONED GMI SUITE IS ALSO 
WEAKENING IN COMPARISON TO ITS APPEARANCE IN PREVIOUS MICROWAVE DATA. 
ENVIRONMENTAL CONDITIONS ARE ASSESSED TO BE FAVORABLE WITH WARM (28-29 
C) SEA SURFACE TEMPERATURES, LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS), 
AND STRONG RADIAL OUTFLOW. HOWEVER, THE SYSTEM HAS MOVED INTO AN AREA 
OF LOWER (BELOW 75 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC) WHICH 
COUPLED WITH THE ERC IS EXPECTED TO CONTINUE WEAKENING THE SYSTEM. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN 
EIR. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, IN GOOD 
AGREEMENT WITH LOWERING AGENCY DVORAK FIXES AND CIMSS OBJECTIVE 
ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   RCTP: T6.5 - 127 KTS
   CIMSS SATCON: 145 KTS AT 211724Z
   CIMSS ADT: 112 KTS AT 211730Z
   CIMSS AIDT: 120 KTS AT 211730Z
   CIMSS D-MINT: 131 KTS AT 211726Z
   CIMSS D-PRINT: 126 KTS AT 211900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: EYEWALL REPLACEMENT CYCLE; LOW OHC

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 29W IS FORECAST TO CONTINUE NORTHWESTWARD AS IT 
APPROACHES THE AXIS OF THE SUBTROPICAL RIDGE (STR) CENTERED TO THE 
NORTHEAST, BEGINNING A POLEWARD TURN BETWEEN TAUS 12 AND 24. AFTER TAU 
60, 29W IS EXPECTED TO TURN AND ACCELERATE NORTHEASTWARD, WITH A 
SHARPER EASTWARD TURN EXPECTED BETWEEN TAUS 72 AND 96 AS THE STEERING 
STR FLATTENS SLIGHTLY DUE TO THE PASSAGE OF THE MID-LATITUDE TROUGH TO 
THE NORTH AT THAT TIME. 29W IS EXPECTED TO MAKE LANDFALL OVER KYUSHU 
JUST AFTER TAU 96 AND CONTINUE TRACKING EASTWARD, SOUTH OF KYOTO. 
EXTRATROPICAL TRANSITION (ETT) IS EXPECTED TO BEGIN BY TAU 72 AS 29W 
APPROACHES THE BAROCLINIC ZONE, WITH COMPLETION OF ETT EXPECTED BY TAU 
120. REGARDING INTENSITY, 29W IS EXPECTED TO CONTINUE ITS RAPID 
WEAKENING TREND AS IT ENTERS AN AREA OF LOW OHC AND IS EXPECTED TO 
BEGIN UPWELLING COOLER SSTS. A SLIGHTLY MORE GRADUAL PERIOD OF 
WEAKENING IS FORECAST BETWEEN TAUS 24 AND 36 AS 29W MOVES OVER AN AREA 
OF SLIGHTLY HIGHER OHCS, BUT THEN CONTINUES TO STEEPLY DROP THEREAFTER 
DUE TO COOL SSTS AND SHARPLY INCREASING VWS BY TAU 72 AS 29W 
APPROACHES THE STRONG UPPER-LEVEL WESTERLIES. DUE TO THE HIGH 
UNCERTAINTY OF THE FORECAST TRACK AND INTENSITY, SIGNIFICANT CHANGES 
TO THE TIMING AND DISTANCE OF CPA TO SASEBO COULD OCCUR IN LATER 
FORECASTS.

MODEL DISCUSSION: TRACK MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT 
WITH ALL PHYSICS-BASED MODELS (EXCLUDING GALWEM AND HAFS-A) NOW 
DEPICTING A (WIDER) RECURVING TRACK, ALTHOUGH THE BULK OF PHYSICS-
BASED MODELS STILL DEPICT BRIEF LANDFALL OVER NORTHERN TAIWAN AND 
CHINA BEFORE REEMERGING OVER THE EAST CHINA SEA AND TRACKING TOWARDS 
KYUSHU. AI-BASED MODELS, WHILE CONSISTENTLY THE EASTERN-MOST GROUPING 
OF TRACKS, CONTINUE TO SHOW A LARGE DIFFERENCE IN TRACK SPEED AMONGST 
THEMSELVES, WITH THE EXPERIMENTAL WEATHERMESH 6 REMAINING JUST WEST OF 
KYUSHU BY TAU 120, WHILE THE AI GFS TRACK IS THE FASTEST, REEMERGING 
OVER WATER AND WELL SOUTH OF TOKYO BY TAU 120. OVERALL CROSS TRACK 
SPREAD IS 700 NM AND ALONG TRACK SPREAD IS 315 NM AT TAU 120, BETWEEN 
THE AI GFS BEING THE FASTEST AND MOST EQUATORWARD, WHILE THE ECMWF IS 
AN OUTLIER TO THE NORTH, BRINGING THE TRACK TOWARDS LANDFALL OVER THE 
KOREAN PENINSULA BY TAU 120. DESPITE THE INCREASE IN AGREEMENT ON THE 
RECURVATURE SCENARIO, THERE IS STILL HIGH UNCERTAINTY AND A 
POSSIBILITY FOR BRIEF LANDFALL OVER TAIWAN AND CHINA, ALTHOUGH NOT 
DEPICTED BY THE JTWC FORECAST, DEPENDING ON HOW THE PASSAGE OF THE 
MID-LATITUDE TROUGH TO THE NORTH AFFECTS THE STEERING STR. THE 
UNCERTAINTY IN TRACK ALSO APPLIES TO THE FORECAST ETT, AS A TRACK THAT 
LINGERS OVER THE COOLER SSTS OF THE EAST CHINA SEA FOR LONGER AND 
UPPER-LEVEL WESTERLIES COULD ACCELERATE THE TIMELINE OF ETT. THE 
OFFICIAL JTWC FORECAST IS ASSESSED WITH LOW CONFIDENCE THROUGHOUT, 
ALIGNED CLOSELY WITH THE AI CONSENSUS AS TRACKS BIFURCATE BEYOND TAU 
48, AND SLIGHTLY SLOWER THAN AI CONSENSUS AT TAU 120 AS THE AI MODELS 
DIVERGE IN TRACK SPEED. MODEL INTENSITY GUIDANCE IS IN GOOD AGREEMENT 
ON A STEEP WEAKENING TREND FOR THE REMAINDER OF THE FORECAST PERIOD, 
ALTHOUGH MANY OF THE JTWC INTENSITY CONSENSUS MEMBERS ARE ASSOCIATED 
WITH TRACKS THAT MAKE LANDFALL OVER TAIWAN AND/OR CHINA. THE OFFICIAL 
JTWC FORECAST INTENSITY IS ASSESSED WITH LOW CONFIDENCE THROUGHOUT THE 
FORECAST PERIOD, AS CHANGES TO THE TRACK WILL CLOSELY AFFECT THE 
INTENSITY. OVERALL, THE JTWC INTENSITY FORECAST CLOSELY FOLLOWS BOTH 
GOOGLE DEEPMIND MODELS AS THEIR TRACK ALIGNS WELL WITH THE JTWC 
FORECAST TRACK.

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