Advisories

WDPN32 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 29W (CHAMPI) WARNING NR 031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.3N 126.0E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 385 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY) 
29W (CHAMPI) WITH AN INCREASINGLY RAGGED EYE THAT HAS COOLED SLIGHTLY 
TO 15 C AS SOME LOW LEVEL CLOUDS BEGIN TO FILL IN. IT MAINTAINS 
EXPANSIVE OUTER BANDING, SPANNING FROM NORTHERN LUZON TO AMAMI 
OSHIMA. 29W HAS CONTINUED TO RAPIDLY WEAKEN, AND THE 1800Z INTENSITY 
WAS REASSESSED TO 125 KTS BASED ON THE CONTINUING ERODING EYEWALL IN 
MICROWAVE IMAGERY. A 212236Z F-16 91 GHZ MICROWAVE IMAGE REVEALS THE 
INNER EYEWALL HAS SINCE FULLY ERODED AND OPENED IN THE SOUTHWESTERN 
QUADRANT AND MAINTAINS A PARTIAL SECONDARY EYEWALL, STRONGEST ON THE 
EASTERN FLANK WITH A DECREASED MOAT OF 25-30 NM IN BETWEEN THE TWO, 
INDICATING A CONTINUED EYEWALL REPLACEMENT CYCLE (ERC). ENVIRONMENTAL 
CONDITIONS ARE ASSESSED AS FAVORABLE WITH LOW (5-10 KTS) VERTICAL 
WIND SHEAR (VWS), WARM (27-28 C) SEA SURFACE TEMPERATURES (SSTS), AND 
STRONG RADIAL OUTFLOW ALOFT, HOWEVER 29W IS WITHIN AN AREA OF LOWER 
(LESS THAN 75 KJ PER CM SQUARED) OCEAN HEAT CONTENT WHICH IS CAUSING 
THE UPWELLING OF COOLER SSTS. THE INITIAL POSITION IS PLACED WITH 
HIGH CONFIDENCE BASED ON THE EYE IN MSI. THE INITIAL INTENSITY IS 
ASSESSED WITH MEDIUM CONFIDENCE DUE TO THE CONTINUED RAPID WEAKENING 
AND UNCERTAINTY ASSOCIATED WITH ERCS, BUT IN GOOD AGREEMENT WITH THE 
RAPIDLY WEAKENING AGENCY DVORAK FIXES AND CIMSS OBJECTIVE ESTIMATES 
LISTED BELOW.

INITIAL WIND RADII BASIS: PARTIAL 212352 METOP-B ASCAT DATA

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS SATCON: 115 KTS AT 212300Z
   CIMSS ADT: 102 KTS AT 212330Z
   CIMSS AIDT: 114 KTS AT 212330Z
   CIMSS D-MINT: 117 KTS AT 212237Z
   CIMSS D-PRINT: 115 KTS AT 220010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: LOW OCEAN HEAT CONTENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INTENSITY FORECAST DEVIATES BELOW
THE PREVIOUS FORECAST BY 10-20 KTS THROUGH TAU 96 DUE TO THE RAPID
WEAKENING OF THE SYSTEM.

FORECAST DISCUSSION: TY 29W IS FORECAST TO CONTINUE NORTHWESTWARD AND 
IS EXPECTED TO BEGIN A MORE POLEWARD TURN AFTER TAU 12 AS IT 
APPROACHES THE AXIS OF THE SUBTROPICAL RIDGE (STR) CENTERED TO THE 
NORTHEAST. BETWEEN TAUS 48 AND 60, 29W WILL BE POLEWARD OF THE STR 
AXIS AND TURN NORTHEASTWARD, ACCELERATING IN TRACK SPEED, AND PASS 
SOUTH OF SASEBO JUST PRIOR TO TAU 96. EXTRATROPICAL TRANSITION (ETT) 
IS EXPECTED TO BEGIN AT TAU 72 AS 29W APPROACHES THE UPPER-LEVEL 
WESTERLIES AND 26 C ISOTHERM. ETT IS EXPECTED TO COMPLETE BY TAU 96, 
BUT COULD COMPLETE SOONER DEPENDING ON THE ULTIMATE TRACK AND SPEED 
OF THE SYSTEM WHICH REMAINS HIGHLY UNCERTAIN. REGARDING INTENSITY, 
29W IS EXPECTED TO CONTINUE RAPIDLY WEAKENING FOR THE REMAINDER OF 
THE FORECAST PERIOD AS IT BEGINS TO UPWELL 26 C SSTS IN ITS WAKE AND 
REMAINS WITHIN AN AREA OF LOW OHC. CONTINUED OR STALLED ERC CAN BE 
EXPECTED TO ADD TO THE WEAKENING TREND. VWS WILL SHARPLY INCREASE 
AFTER TAU 60 AS THE SYSTEM APPROACHES THE UPPER-LEVEL WESTERLIES, IN 
TIME WITH THE ONSET OF ETT. THE SYSTEM IS EXPECTED TO COMPLETE ETT 
BELOW TROPICAL STORM STRENGTH, WITH THE POSSIBILITY OF DISSIPATING 
PRIOR TO COMPLETING ETT, ALTHOUGH NOT DEPICTED IN THE OFFICIAL 
FORECAST.

MODEL DISCUSSION: TRACK MODEL GUIDANCE CONTINUES TO COME INTO BETTER 
AGREEMENT, WITH BOTH PHYSICS AND AI BASED MODELS NOW DEPICTING A 
RECURVATURE SCENARIO, HOWEVER THE FORMER REMAINS GROUPED TO THE WEST 
WITH BRIEF LANDFALL OVER NORTHERN TAIWAN, WHILE THE AI MODELS MAKE UP 
THE EASTERN GROUPING, PASSING BETWEEN TAIWAN AND ISHIGAKIJIMA. 
PHYSICS-BASED MODEL FIELDS INDICATE THE PASSING MID-LATITUDE TROUGH 
WILL WEAKEN THE STEERING STR LESS THAN AI-BASED MODEL FIELDS, AND 
THUS DEPICT A WIDER RECURVATURE. TRACK SPEED ALSO DIVERGES IN THE 
LATER TAUS WITH THE ONSET OF ETT AND SUBSEQUENT ACCELERATION IN TRACK 
SPEED. CROSS TRACK SPREAD IS 770 NM BETWEEN THE FASTEST OF AIGEFS 
REACHING SOUTH OF TOKYO WHILE NAVGEM LIES NORTH OF TAIWAN. THE AI 
MODELS ALONE HAVE AN ALONG TRACK SPREAD OF 260 NM AT TAU 96 BETWEEN 
AIGEFS AND THE SLOWEST, EXPERIMENTAL WEATHER MESH. THE OFFICIAL JTWC 
FORECAST TRACK IS PLACED WITH LOW CONFIDENCE THROUGHOUT, IN LINE WITH 
THE AI CONSENSUS AND HEDGING BETWEEN THE AI CONSENSUS AND GOOGLE 
DEEPMIND AT TAU 96. REGARDING INTENSITY, ALL MODEL INTENSITY GUIDANCE 
IS IN GOOD AGREEMENT ON A SHARP WEAKENING TREND FOR THE REMAINDER OF 
THE FORECAST PERIOD DESPITE THE VARYING TRACKS AND POTENTIAL BRIEF 
LANDFALLS. THE OFFICIAL JTWC FORECAST INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE OUT TO TAU 72 AND LOW CONFIDENCE THEREAFTER, DUE TO 
ITS DEPENDENCE ON THE ULTIMATE TRACK OF 29W AND THE POSSIBILITY FOR 
EARLIER ETT AND SUBSEQUENT DISSIPATION. THE INTENSITY FORECAST IS 
CLOSELY IN LINE WITH BOTH GOOGLE DEEPMIND MODELS SINCE THE FORECAST 
TRACK CLOSELY MATCHES THE GOOGLE DEEPMIND AS WELL.

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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