Advisories

WDPN32 PGTW 210300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.1N 130.1E
   INITIAL INTENSITY: 155 KTS
   GEOGRAPHIC REFERENCE: 520 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 70 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) CONTINUES TO DEPICT
SUPER TYPHOON (STY) 29W AS A POWERFUL STORM WITH A WELL-DEFINED EYE
AND SYMMETRICAL CLOUD CANOPY, RINGED WITH SPIRAL BANDS OF DEEP
CONVECTION. CLOUD TOPS HAVE WARMED SLIGHTLY, WITH THE COOLEST
TEMPERATURES MEASURED NEAR THE EYE MAINTAINING BETWEEN -70C AND
-75C, SIGNALING SOME SLIGHT WEAKENING. THE ENVIRONMENT REMAINS
HIGHLY FAVORABLE, CHARACTERIZED BY LOW (0-5 KTS) VERTICAL WIND
SHEAR (VWS), WARM (28-29 C) SEA SURFACE TEMPERATURES, HIGH (100-125
KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC), AND ROBUST RADIAL
OUTFLOW; HOWEVER, THE SSTS AND OHC HAVE BECOME SLIGHTLY LESS
FAVORABLE OVER THE PAST 6 HOURS. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE CLEAR EYE PRESENT IN ANIMATED
MSI. THE INITIAL INTENSITY OF 155 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE GOOD AGREEMENT BETWEEN THE AGENCY DVORAK
FIXES AND CIMSS AUTOMATED 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 ADT: 137 KTS AT 202300Z
   CIMSS AIDT: 152 KTS AT 202300Z
   CIMSS D-PRINT: 155 KTS AT 202300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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: 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, THE TROUGH WILL HAVE PASSED, LEAVING A 
BREAK BETWEEN THE ORIGINAL STEERING RIDGE AND A FORMING, SHALLOWER 
RIDGE CENTERED OVER SOUTHEASTERN ASIA. AS 29W TRACKS WEST-
NORTHWESTWARD, IT IS EXPECTED TO ENCOUNTER THIS BREAK AT AROUND TAU 
24-36. 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 36-72, 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 36, 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 12 AS IT TRACKS INTO PROGRESSIVELY LOWER VALUES. BY TAU 24, OHC IS 
EXPECTED TO DROP TO AROUND 50 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 12-24. AROUND TAU 36, 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 BETWEEN TAU 36-48. 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 24. FOLLOWING TAU 24, 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 
600 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 NORTH OF TOKYO WHILE EXPERIMENTAL WINDBORNE IS 
STILL OFF THE SOUTHERN COAST OF KYUSHU. 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 
INTENSITY MEMBER THAT INDICATES A RECURVE AND EXTRATROPICAL 
TRANSITION. 
THE JTWC INTENSITY FORECAST IS PLACED WITH OVERALL LOW CONFIDENCE DUE 
TO THE UNCERTAINTY SURROUNDING THE WEAKENING TREND AND RECURVE 
SCENARIO.

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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