Advisories

WDPN32 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.1N 142.3E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 156 NM WEST-SOUTHWEST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
DETERIORATING SYSTEM; THE PREVIOUSLY WELL-RESOLVED, WARM EYE EYEWALL 
COMPLEX FILLED RAPIDLY POST-180300Z, BECOMING COMPLETELY OBSCURED 
BY 180400Z. CURRENT MSI AND ENHANCED INFRARED (EIR) LOOPS RESOLVE 
NO CLOUD-FREE EYE SIGNATURE; HOWEVER, VIGOROUS VORTICAL HOT 
TOWERS (VHTS) RESIDE ALONG THE SOUTHERN SECTOR OF A NASCENT, 
RE-CONSOLIDATING EYEWALL. A 180618Z GMI 89GHZ MICROWAVE PASS 
CONFIRMED AN ACTIVE SECONDARY EYEWALL FORMATION (SEF) EVENT, WITH 
THE CIMSS M-PERC HOVMOLLER DIAGRAM RESOLVING THE CONCENTRIC OUTER 
EYEWALL BAND ANCHORED APPROXIMATELY 40 KM DISTANT FROM THE LOW-LEVEL 
CIRCULATION CENTER (LLCC). IN ADDITION TO COMPLICATED ERC DYNAMICS, 
DRY MID-LEVEL AIR ENTRAINMENT IS VIGOROUSLY INTRUDING INTO THE 
CYCLONE'S INNER CORE FROM THE EAST. THIS THERMODYNAMIC EROSION IS 
CLEARLY RESOLVED IN HAFS-A RELATIVE HUMIDITY CROSS-SECTIONS AND 
COINCIDES WITH GMI BRIGHTNESS TEMPERATURE ANOMALIES. THE INITIAL 
POSITION IS ASSESSED WITH MEDIUM CONFIDENCE OWING TO THE OBSCURED 
LLCC, INTERPOLATED VIA REMNANT CORE CLOUD-TOP CURVATURE AND ACTIVE 
CONVECTIVE FLARES IN EIR. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE. POST-ANALYSIS OF EARLIER POSITIONS JUSTIFIED AN 
UPGRADE IN THE 180000Z INTENSITY TO 145 KNOTS. THE RECENT EYE 
COLLAPSE HAS INDUCED A STEEP DECAY IN THE MAJORITY OF OBJECTIVE 
ESTIMATES, EXCLUDING CIMSS ADT CI VALUES; HOWEVER, CONSTRAINTS ARE 
BEING APPLIED, AND RAW T-NUMBERS ARE SIGNIFICANTLY DEPRESSED. THE 
INITIAL INTENSITY IS SET CONSERVATIVELY AT 130 KNOTS BASED ON A 
SYNTHESIS OF THE MULTI-AGENCY ESTIMATES. THE SYNOPTIC ENVIRONMENT 
REMAINS FAVORABLE, CHARACTERIZED BY LOW DEEP-LAYER VWS, STRONG 
RADIAL OUTFLOW ALOFT, AND WARM SSTS; HOWEVER, THE ONGOING ERC AND 
ENTRAINMENT OF DRY AIR INTO THE CORE WILL DRAG THE SYSTEM INTO A 
TEMPORARY WEAKENING PHASE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF AN EXTENSION OF A
SUBTROPICAL RIDGE (STR) CENTERED NEAR HONG KONG. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T7.0 - 140 KTS 
   RCTP: T7.0 - 140 KTS 
   CIMSS SATCON: 109 KTS AT 180500Z
   CIMSS ADT: 134 KTS AT 180540Z
   CIMSS AIDT: 126 KTS AT 180540Z
   CIMSS D-MINT: 121 KTS AT 180618Z
   CIMSS D-PRINT: 124 KTS AT 180600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG DUAL-CHANNEL
   OTHER FACTORS: EYEWALL REPLACEMENT CYCLE (ERC). 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: SUPER TYPHOON (STY) 29W IS FORECAST TO GRADUALLY
TURN NORTHWESTWARD OVER THE NEXT 12 HOURS AND MAINTAIN THIS STEADY
TRAJECTORY THROUGHOUT THE FORECAST. THE CONTROLLING SYNOPTIC DRIVER 
IS THE RIDGE EXTENSION CENTERED NEAR HONG KONG. AROUND TAU 24, THE 
STR IS PROJECTED TO SEPARATE INTO TWO DISTINCT HIGH-PRESSURE CENTERS
(ONE NORTHEAST OF THE CYCLONE AND A LARGER CELL NEAR HONG KONG). 
THE RESULTANT COL WEAKNESS WILL INDUCE A SLIGHT DECELERATION IN
TRANSLATION SPEED FROM TAU 24 TO TAU 36. POST-TAU 36, 29W WILL 
RE-ACCELERATE TO 12-13 KNOTS AS THE WESTERN RIDGE CELL BECOMES THE 
PRIMARY STEERING INFLUENCE. BY TAU 72, A MID-LATITUDE SHORTWAVE 
TROUGH PASSES OVER THE KOREAN PENINSULA, FRACTURING THE RIDGE AND 
ESTABLISHING A STEERING WEAKNESS ACROSS THE EAST CHINA SEA. AS 29W 
ENTERS THE EQUATORWARD QUADRANT OF THIS COL NEAR TAU 72, IT WILL 
DECELERATE MARKEDLY UNDER A RELAXED PRESSURE GRADIENT. WHILE THE 
BASELINE TRACK PROG STRETCHES NORTHWESTWARD THROUGH TAU 120,
GUIDANCE BIFURCATES SHARPLY POST-TAU 72, SENSITIVE TO THE DEPTH OF 
THE APPROACHING TROUGH. ROUGHLY HALF OF THE CONSENSUS DEPICTS A 
RECURVATURE INTO THE EAST CHINA SEA, WHILE THE REMAINING MEMBERS 
TRACK THE CYCLONE ON A STRAIGHT TRAJECTORY TOWARDS SOUTHERN TAIWAN. 
REGARDING INTENSITY: THE COMBINED FORCES OF ERC DRY AIR ENTRAINMENT 
HAVE DEGRADED THE INNER CORE OVER THE PAST SIX HOURS. 29W IS FORECAST  
TO CONTINUE ITS TEMPORARY DECAY, BOTTOMING OUT NEAR 120 KNOTS AT TAU 
12, PRIOR TO OUTER EYEWALL CONSOLIDATION AND REINTENSIFICATION. THE 
CYCLONE TRANSITS OVER A POOL OF ELEVATED OHC FROM TAU 24 TO TAU 48, 
WHICH SHOULD FUEL A SECONDARY INTENSITY PEAK OF AT LEAST 140 KNOTS.  
HOWEVER, INCIPIENT CYCLES OF SEF ARE HIGHLY PLAUSIBLE, WHICH WOULD 
MATERIALLY ALTER THE MAGNITUDE AND SHAPE OF THE INTENSITY CURVE. 
BEYOND TAU 72, AS TRANSLATION SPEEDS DECREASE, SELF-INDUCED COLD 
WATER UPWELLING COMBINED WITH INCREASING VWS WILL PROMPT A GRADUAL 
DECAY PROFILE AS THE CYCLONE APPROACHES TAIWAN. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT THROUGH 
TAU 72. CROSS-TRACK SPREAD IS MINIMAL THROUGH TAU 24, AND GRADUALLY
INCREASES TO 90NM BY DAY THREE. UP TO THIS POINT IN THE FORECAST,
THE ECMWF TRACKER IS POSITIONED ON THE SOUTHERN EDGE OF THE GUIDANCE 
ENVELOPE, WHILE THE GOOGLE DEEPMIND AND EC-AIFS AI ENSEMBLE ARE 
POSITIONED ON THE NORTHERN EDGE. TAU 72 IS THE INFLECTION POINT WHERE 
THE MODELS DIVERGE INTO TWO CAMPS. ALL OF THE AI MODELS BEGIN TO SPLIT 
OFF AND BREAK TO THE NORTH WITH THE TWO MENTIONED EARLIER BEING THE 
MOST AGGRESSIVE NORTH MOVERS THROUGH TAU 120. THE OTHER AI MODELS 
DEPICT A VERY SHALLOW TURN, JUST A BIT NORTH OF NORTHWEST THROUGH 
TAU 120. THE PHYSICS MODELS ALL CONTINUE STRAIGHT NORTHWESTWARD AT A 
SLIGHTLY FASTER SPEED OF ADVANCE. GEFS IS POSITIONED ON THE SOUTHERN 
EDGE, MOVING INTO THE LUZON STRAIT WHILE NAVGEM IS ON THE NORTHERN 
EDGE, MOVING TOWARDS CENTRAL TAIWAN, AT TAU 120. CROSS-TRACK SPREAD 
INCREASES TO 310NM BY TAU 120 BETWEEN THE OUTLIERS. THE EXPERIMENTAL 
JTWC SUPER-ENSEMBLE DEPICTS A STRONG BIFURCATION SCENARIO, WITH 
ROUGHLY HALF OF THE NEARLY 300 MEMBERS RECURVING AND THE OTHER 
MAINTAINING A STRAIGHT TRACK. THE JTWC FORECAST IS CONSISTENT WITH 
THE PREVIOUS TRACK FORECAST AND NEAR THE EC-AIFS TRACKER. INTENSITY 
GUIDANCE IS IN GOOD OVERALL AGREEMENT, WITH CTCX, COTC AND SHIPS 
SHOWING A SHARP DECREASE THROUGH TAU 12 FOLLOWED BY REINTENSIFICATION 
TO 130-140 KNOTS BY TAU 48 BEFORE RENEWED WEAKENING THROUGH THE END 
OF THE FORECAST. THE JTWC FORECAST IS PLACED NEAR THE CTCX TRACKER
THROUGH THE FORECAST PERIOD. 

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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