Advisories

WDPN32 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 29W (CHAMPI) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.5N 141.4E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 187 NM WEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT INNER CORE OF DEEP CONVECTION, FEATURING RAPIDLY DEVELOPING 
VORTICAL HOT TOWERS (VHTS) DEEPENING CONCENTRICALLY AND INITIATING
A NEW EYE FORMATION. THE RECENT SATELLITE CHANGES HAVE DRIVEN THE
CIMSS ADT TECHNIQUE TO CHANGE FROM UNIFORM CDO TO AN ACTIVE PINHOLE 
EYE SCHEME, WITH RAW T-NUMBERS RAPIDLY INCREASING TO T6.5. THERE HAS 
BEEN A LACK OF MICROWAVE IMAGERY COVERAGE OF 29W SINCE 180621Z; 
CONSEQUENTLY, THE EXACT PROGRESSION OF THE EYEWALL REPLACEMENT CYCLE 
(ERC) CANNOT BE RESOLVED BEYOND OBSERVATIONS OF CLOUD CLEARING WITHIN 
THE CENTRAL CORE. THE INITIAL POSITION IS ASSESSED WITH MEDIUM 
CONFIDENCE, POSITIONED NEAR THE INCIPIENT EYE RESOLVED IN EIR. 
SIMILARLY, THE ABSENCE OF HIGH-RESOLUTION SURFACE WIND MEASUREMENTS 
CAPABLE OF SAMPLING THE COMPACT INNER-CORE WIND FIELDS FOR THE PAST 
36 HOURS ELEVATES INTENSITY UNCERTAINTY. ACCORDINGLY, INITIAL 
INTENSITY IS HEDGED CONSERVATIVELY AT 120 KNOTS BASED ON A SYNTHESIS 
OF MULTI-AGENCY SUBJECTIVE AND CIMSS OBJECTIVE SATELLITE ESTIMATES. 
IN THE UPPER-LEVELS, THE ANTICYCLONE POSITIONED TO THE NORTHWEST 
EXHIBITS WEAKENING AND WESTWARD DISPLACEMENT, REDUCING THE NORTHERLY 
SHEAR THAT WAS INFLUENCING THE SYSTEM EARLIER. ENVIRONMENTAL 
CONDITIONS REMAIN FAVORABLE, WITH LOW VWS, VERY WARM SSTS, HIGH OHC 
AND ROBUST RADIAL OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEVELOPING
SUBTROPICAL RIDGE (STR) CENTER TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T7.0 - 140 KTS 
   RCTP: T6.5 - 127 KTS
   CIMSS ADT: 117 KTS AT 181130Z
   CIMSS AIDT: 126 KTS AT 181130Z
   CIMSS D-MINT: 123 KTS AT 181011Z
   CIMSS D-PRINT: 123 KTS AT 181200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THE TRACK OF TYPHOON 29W HAS SHIFTED WEST-
NORTHWESTWARD OVER THE PAST SIX HOURS, AS THE DEEP-LAYER RIDGE
EXTENSION DRAPED ACROSS THE NORTHERN PACIFIC HAS PINCHED OFF INTO A 
DISCRETE SECONDARY ANTICYCLONE TO THE NORTHEAST. SIMULTANEOUSLY, THE 
TRANSLATION SPEED HAS DECREASED SLIGHTLY AS A LOCALIZED COL REGION 
DEVELOPS NORTH OF THE SYSTEM, RELAXING THE STEERING GRADIENT. THIS 
WEAKNESS WILL BE SUPPRESSED BY A EASTWARD EXTENSION OF THE PRIMARY 
STR (CENTERED NEAR HONG KONG) WITHIN 24 TO 36 HOURS. THIS CELL IS 
PROJECTED TO TRANSLATE RAPIDLY EASTWARD NORTH OF 29W FROM TAU 36 TO 
TAU 72, REINFORCING THE NORTHWESTWARD TRAJECTORY AND ACCELERATING THE 
CYCLONE TO APPROXIMATELY 13 KNOTS. BY TAU 72, A PASSING POLAR TROUGH 
OVER THE KOREAN PENINSULA WILL WEAKEN THE RIDGE, OPENING A STEERING 
COL ACROSS THE EAST CHINA SEA. THE RESULTANT RELAXATION OF THE 
STEERING GRADIENT WILL INDUCE GRADUAL DECELERATION THROUGH THE END OF 
THE FORECAST. REGARDING INTENSITY, THE ERC APPEARS TO HAVE COMPLETED, 
AND THE SYNOPTIC ENVIRONMENT FAVORS INCIPIENT REINTENSIFICATION. THE 
SYSTEM WILL TRAVERSE AN EXTENSIVE POOL OF THE WARMEST, HIGHEST OHC 
WATERS IN THE WESTERN PACIFIC OVER THE NEXT 48 HOURS, PROVIDING 
ROBUST THERMODYNAMIC ENERGY TO SUPPORT SUSTAINED INTENSIFICATION. THE 
PRIMARY LIMITING FACTOR WILL BE THE HIGH PROBABILITY OF ADDITIONAL 
PERIODS OF ERC, THE TIMING, DURATION AND SCALE OF WHICH REMAIN HIGHLY 
UNCERTAIN. THE CYCLONE IS FORECAST TO RE-ATTAIN SUPER TYPHOON 
INTENSITY WITHIN THE NEXT 12 HOURS, PEAKING NEAR 140 KNOTS BY TAU 24. 
DEPENDING ON THE ERCS, THE SYSTEM COULD REACH A HIGHER PEAK 
INTENSITY, AND SIGNIFICANT DEVIATIONS BELOW 140 KNOTS ARE ALSO 
POSSIBLE. BY TAU 72, INCREASING VERTICAL WIND SHEAR AND UPWELLING OF 
COLD WATER AMID THE DECELERATING SPEED PROFILE WILL TRUNCATE 
DEVELOPMENT, PROMPTING A STEADY DECAY AFTER TAU 72, AS THE SYSTEM 
APPROACHES TAIWAN.

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN EXCELLENT AGREEMENT 
THROUGH TAU 72, AT WHICH THE ENVELOPE SHARPLY DISPERSES. CROSS-
TRACK SPREAD WIDENS FROM 55 NM AT TAU 60 TO 100 NM BY TAU 72. 
CONCURRENT WITH PRIOR CYCLES, THE AI MODELS BIFURCATE POLEWARD AS 
EARLY AS TAU 60, ACCELERATING A NORTH-NORTHEASTWARD RECURVATURE BY 
TAU 72 AS THE SYSTEM IS PULLED NORTHWARD INTO THE WEAKNESS IN THE 
RIDGE; IN CONTRAST, THE PHYSICS-BASED MODELS MAINTAIN A LINEAR 
NORTHWESTWARD TRAJECTORY THROUGH TAU 72. THIS SCHEMA CONTINUES 
THROUGH TAU 120, WITH GOOGLE DEEPMIND AND EC-AIFS ENSEMBLE REMAINING 
THE MOST PROGRESSIVE NORTHERN OUTLIERS DIRECTING THE TRACK TOWARD 
MIYAKOJIMA. THE PHYSICS MODELS HAVE CONVERGED ALONG A FLATTER 
HEADING TARGETED TOWARD SOUTHERN TAIWAN, REDUCING OVERALL CROSS-TRACK 
SPREAD AT DAY 5 TO 340 NM. MULTI-MODEL ENSEMBLES DEPICT EXTREME LONG-
RANGE DISPERSION; THE JTWC EXPERIMENTAL SUPER-ENSEMBLE EXHIBITS A 
MEMBER SPREAD BOUNDED BY SOUTHERN TAIWAN AND MIYAKOJIMA AT TAU 120, A 
BOUNDARY SPANNING FROM HONG KONG TO SASEBO IN BEYOND-DAY-5 
EXTENSIONS. THE JTWC TRACK PATH FAVORS THE DETERMINISTIC ECMWF AND 
ECEPS MEAN TRACKERS. INTENSITY GUIDANCE CONCURS STRONGLY ON THE 
INTENSITY PROFILE. THE JTWC INTENSITY FORECAST IS HEDGED 5 KNOTS 
ABOVE THE HAFS-A, HWRF, CTCX, AND DEEPMIND GROUP THROUGH TAU 48, 
REPRESENTING THE HIGH-END BOUNDARY PRIOR TO DOWNSTREAM DECAY.

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