Advisories

WDPN32 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4N 131.5E
   INITIAL INTENSITY: 160 KTS
   GEOGRAPHIC REFERENCE: 583 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 68 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SUPER
TYPHOON (STY) 29W AS A TEXTBOOK TYPHOON, WITH STUNNING SPIRAL BANDS
OF DEEP CONVECTION, A SYMMETRICAL UPPER-LEVEL CLOUD CANOPY, AND A
CONTRACTING EYE. THE WELL-DEFINED EYE MEASURED 30 NM IN DIAMETER
WITH A CENTER TEMPERATURE OF +21C. ENVIRONMENTAL ANALYSIS REVEALED
IDEAL CONDITIONS FOR 29W, CHARACTERIZED BY LOW (5-10 KTS) VERTICAL
WIND SHEAR (VWS), VERY WARM (30-31 C) SEA SURFACE TEMPERATURES
(SST), HIGH (125-150 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC),
AND ROBUST RADIAL OUTFLOW. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE EYE IN ANIMATED EIR. THE INITIAL INTENSITY
OF 160 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY
DVORAK FIXES, WHICH HAVE ALL BEEN 7.5 FOR SEVERAL FIX CYCLES,
SUPPLEMENTED BY THE AUTOMATED CIMSS INTENSITY ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.5 - 155 KTS
   RJTD: T7.5 - 155 KTS
   RCTP: T7.5 - 155 KTS
   CIMSS SATCON: 154 KTS AT 201700Z
   CIMSS ADT: 137 KTS AT 201830Z
   CIMSS AIDT: 145 KTS AT 201830Z
   CIMSS D-MINT: 147 KTS AT 201702Z
   CIMSS D-PRINT: 156 KTS AT 201830Z

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

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: STY 29W (CHAMPI) IS FORECAST TO CONTINUE
TRACKING WEST-NORTHWESTWARD FOR THE NEXT 36 HOURS WHILE IT REMAINS
ON THE SOUTHWESTERN PERIPHERY OF THE STEERING STR CENTERED TO THE
NORTHEAST. BEGINNING IMMINENTLY THROUGH TAU 12, A SHORTWAVE TROUGH
PASSING TO THE NORTH IS EXPECTED TO BREAK DOWN THE STR, FORCING IT
TO RETREAT EASTWARD. BY ABOUT TAU 24-48, THE TROUGH WILL HAVE
PASSED, LEAVING A BREAK BETWEEN THE ORIGINAL STEERING RIDGE AND A
FORMING, SHALLOWER RIDGE CENTERED OVER SOUTHEASTERN ASIA. AS 29W
TRACK WEST-NORTHWESTWARD, IT IS EXPECTED TO ENCOUNTER THIS BREAK AT
AROUND TAU 36. AT THAT POINT, 29W IS FORECAST TO SLOW DOWN AND
TRACK INTO THE WEAKNESS WHILE THE ORIGINAL STR RETAINS STEERING
AUTHORITY. 29W IS FORECAST TO RECURVE ABOUT THE STR BETWEEN TAU
48-72, CROSSING THE RIDGE AXIS AROUND TAU 60. AFTER TAU 72, 29W IS
EXPECTED TO TRACK NORTHEASTWARD, MAKING LANDFALL IN KYUSHU JUST
BEFORE TAU 120 AND BEGINNING EXTRATROPICAL TRANSITION SHORTLY AFTER
LANDFALL. HOWEVER, THERE EXISTS AN ALTERNATE SCENARIO WHERE THE
STEERING RIDGE BUILDS BACK TO THE WEST QUICKLY AROUND TAU 48,
BEFORE 29W CAN RECURVE. SHOULD THE RIDGE BUILD WESTWARD, 29W COULD
CONTINUE ITS WEST-NORTHWESTWARD TRAJECTORY AND MAKE LANDFALL IN
TAIWAN, VICE KYUSHU. THE ALTERNATE, 'STRAIGHT RUNNING' TRACK HAS
BEEN CONSISTENTLY DEPICTED IN GLOBAL MODELS SUCH AS GFS AND ECMWF.
THE JTWC FORECAST REFLECTS THE RECURVE SCENARIO DUE TO THE
HISTORICAL HIGH ACCURACY OF THE AI MODELS THAT DEPICT A RECURVE
(INCLUDING GOOGLE DEEPMIND), AND HAVE ALREADY PROVEN CORRECT IN A
PAST STORM WITH A VERY SIMILAR ATMOSPHERIC SETUP. 

REGARDING INTENSITY, CHAMPI IS FORECAST TO GRADUALLY WEAKEN THROUGH
TAU 24 AS IT EXITS THE POOL OF EXCEPTIONALLY WARM OHC AND INTO
PROGRESSIVELY LOWER VALUES. BY TAU 24, OHC IS EXPECTED TO DROP TO
BELOW 75 KJ PER CM SQUARED, WHICH, WHEN COUPLED WITH 29W SLOWING TO
TURN INTO THE RIDGING WEAKNESS, IS EXPECTED TO EXACERBATE THE
IMPACTS OF CHAMPI'S UPWELLING. AS A RESULT, CHAMPI IS FORECAST TO
RAPIDLY WEAKEN FROM TAU 24-36. BETWEEN TAU 48-60, 29W IS FORECAST
TO TRACK THROUGH A PATCH OF ELEVATED (100-125 KJ PER CM SQUARED)
OHC, WHICH IS ANTICIPATED TO TEMPORARILY SLOW THE WEAKENING TREND.
29W IS FORECAST TO RAPIDLY WEAKEN FROM TAU 60-96 AS IT OFFICIALLY
CROSSES THE 26C ISOTHERM AND LOSES OCEANIC SUPPORT. ADDITIONALLY,
IT IS EXPECTED TO ENCOUNTER DRY AIR AND INCREASING VWS WHILE IT
TRACKS THROUGH THE EAST CHINA SEA, CONTRIBUTING TO RAPID
UNRAVELING. BY TAU 96-120, CHAMPI IS FORECAST TO BEGIN ITS FINAL
APPROACH INTO KYUSHU, INTRODUCING LAND INTERACTION AS AN ADDED
COMPOUNDING INFLUENCE TO WEAKENING. BY TAU 120, 29W IS EXPECTED TO
BE ON THE FRINGES OF THE UPPER-LEVEL JET AND THE BAROCLINIC ZONE,
INITIATING THERMAL ADVECTION AND THUS BEGINNING EXTRATROPICAL
TRANSITION.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH TAU 36. FOLLOWING TAU 36, MODEL GUIDANCE
STRUGGLES TO INTERPRET THE COMPLEX RIDGING LAYOUT. THERE IS A
DISTINCT BIFURCATION BETWEEN THE PHYSICS-BASED MODELS AND THE
AI-BASED MODELS: THE PHYSICS-BASED MODELS -- INCLUDING GFS, GEFS,
ECMWF, AND ECENS -- DEPICT A STRAIGHT RUNNING TRACK THAT PROGRESSES
WEST-NORTHWESTWARD THROUGH TAU 120, WITH LANDFALLS IN TAIWAN AND
CHINA. GSM, NAVGEM, AND THE AI-BASED MODELS -- INCLUDING GOOGLE
DEEPMIND, AI GFS, AI ECMWF, AI ECENS, AND EXPERIMENTAL WINDBORNE --
DEPICT A RECURVE SCENARIO WHERE 29W CURVES INTO THE WEAKNESS
CREATED BY THE SHORTWAVE TROUGH AND TRACKS NORTHEASTWARD TOWARDS
JAPAN. EVEN WITHIN THE RECURVE SCENARIO, A SPLIT BETWEEN FASTER
MODELS AND SLOWER MODELS EMERGES. THERE IS A 510 NM ALONG-TRACK
SPREAD BETWEEN THE FASTEST MEMBER (GOOGLE DEEPMIND) AND THE SLOWEST
MEMBER (EXPERIMENTAL WINDBORNE) AT TAU 120. AT TAU 120, GOOGLE
DEEPMIND IS NORTHEAST OF KYOTO WHILE EXPERIMENTAL WINDBORNE IS
STILL WELL WITHIN THE EAST CHINA SEA. THERE IS SIGNIFICANT
UNCERTAINTY IN THE LATE-TERM JTWC TRACK FORECAST DUE TO BOTH THE
BIFURCATION AND SPEED DIFFERENCE IN RECURVING MEMBERS, SO THE JTWC
TRACK FORECAST IS PLACED CLOSE TO THE AI MODEL CONSENSUS WITH
OVERALL LOW CONFIDENCE.

RELIABLE INTENSITY AIDS ARE IN GOOD AGREEMENT WITH REGARD TO A
GENERAL WEAKENING TREND FOR THE DURATION OF THE FORECAST PERIOD.
HOWEVER, IT IS WORTH NOTING THAT ALL MEMBERS OF THE JTWC INTENSITY
CONSENSUS DEPICT A LANDFALL SCENARIO, AND THEREFORE DISSIPATION
OVER LAND. CONSEQUENTLY, INTENSITY CONSENSUS MEMBERS DEPICT A MUCH
FASTER WEAKENING TREND, WHICH IS POSSIBLE SHOULD CHAMPI FAVOR THE
STRAIGHT RUNNER TRACK. BECAUSE JTWC IS FORECASTING THE RECURVE, THE
INTENSITY FORECAST IS CLOSELY ALIGNED WITH GOOGLE DEEPMIND, THE
ONLY INDIVIDUAL MEMBER THAT INDICATES A RECURVE AND EXTRATROPICAL
TRANSITION. THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM
CONFIDENCE FROM TAU 0-72, THEN LOW CONFIDENCE FROM TAU 72-120.

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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