Advisories

WDPN32 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.1N 143.4E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 72 NM WEST-SOUTHWEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 47 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS SUPER TYPHOON 
(STY) 29W (CHAMPI) WITH A CLOUD FREE EYE THAT HAS WARMED TO 20 C AND A 
COMPACT CDO WITH CLOUD TOPS THAT HAVE ALSO SLIGHTLY WARMED, 
PARTICULARLY IN THE SOUTHEASTERN QUADRANT, WHILE A MORE DISPLACED 
CONVECTIVE BAND ON THE WESTERN FLANK HAS BEGUN TO DEVELOP. AN EYEWALL 
REPLACEMENT CYCLE (ERC) MAY HAVE RESUMED AS A 172152Z SSMIS PASS 
REVEALS A PARTIAL SECONDARY EYEWALL STRONGEST IN THE NORTHEASTERN 
QUADRANT AND VISIBLE BUT WEAKER ON THE SOUTHERN SEMICIRCLE, WHILE 
STILL FULLY OPEN IN THE NORTHWESTERN QUADRANT. A SIMILAR DEPICTION IS 
SUPPORTED IN ANIMATED RADAR IMAGERY FROM GUAM, AND A 30 NM MOAT 
BETWEEN THE TWO EYEWALLS. ENVIRONMENTAL CONDITIONS ARE ASSESSED AS 
HIGHLY FAVORABLE WITH WARM (28-29 C) SEA SURFACE TEMPERATURES (SSTS), 
LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), AND STRONG 
RADIAL OUTFLOW ALOFT AS WELL AS AN EQUATORWARD OUTFLOW CHANNEL. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN 
MSI AND RADAR IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH HIGH 
CONFIDENCE, HEDGED SLIGHTLY LOWER THAN THE AGENCY DVORAK FIXES AND 
OBJECTIVE ESTIMATES DUE TO THE ASSESSED RESUMPTION OF ERC AND 
RESULTANT TEMPORARY DETERIORATION OF THE CDO.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: EASTWARD EXTENSION OF A SUBTROPICAL
RIDGE CENTERED TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   RCTP: T7.0 - 140 KTS 
   CIMSS SATCON: 134 KTS AT 172152Z
   CIMSS ADT: 137 KTS AT 172340Z
   CIMSS AIDT: 140 KTS AT 172340Z
   CIMSS D-MINT: 116 KTS AT 172313Z
   CIMSS D-PRINT: 137 KTS AT 172340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: EQUATORWARD OUTFLOW CHANNEL AND 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: CHAMPI HAS CONTINUED ON A WESTWARD TRACK AS THE 
EASTWARD EXTENSION OF THE SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE 
WEST-NORTHWEST MAINTAINS STEERING CONTROL. BY TAU 12, THE EXTENSION 
WILL REFORM INTO A SEPARATE STR, AND THE RESULTANT WEAKNESS IN THE 
RIDGING COMPLEX BETWEEN THE NEW STR AND THE WESTERN STR WILL CAUSE 29W 
TO TURN POLEWARD FOR THE REMAINDER OF THE FORECAST PERIOD, WITH THE 
NEWLY FORMED STR BECOMING THE DOMINANT STEERING FACTOR. REGARDING 
INTENSITY, 29W IS EXPECTED TO GRADUALLY INTENSIFY AND PLATEAU FOR THE 
NEXT 72 HOURS AS ENVIRONMENTAL CONDITIONS REMAIN HIGHLY FAVORABLE. A 
PEAK INTENSITY OF 140 KTS IS EXPECTED BETWEEN TAUS 24 AND 48 AS VWS 
WILL ABATE TO UNDER 10 KTS AND 29W ENTERS AN AREA OF HIGH (140-150 KJ 
PER CM SQUARED) OCEAN HEAT CONTENT (OHC). HOWEVER, PROLONGED OR EVEN 
MULTIPLE ERCS ARE POSSIBLE DURING THIS TIME FRAME, WHICH ADDS 
UNCERTAINTY AND THE POTENTIAL FOR SHORT TERM FLUCTUATIONS ABOVE OR 
BELOW THE OFFICIAL INTENSITY FORECAST, DUE TO THE INHERENTLY DIFFICULT 
NATURE IN FORECASTING THESE INTERNAL DYNAMICS. BEYOND TAU 72, A 
GRADUAL WEAKENING TREND IS EXPECTED TO BEGIN AS 29W WILL SLIGHTLY SLOW 
IN TRACK SPEED, ENTER AN AREA OF LOWER OHC, AND BEGIN UPWELLING COOLER
SSTS.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE
FORECAST PERIOD, WITH A CROSS-TRACK AND ALONG-TRACK SPREAD OF 145 NM 
AT TAU 120, COMPRISED OF GOOGLE DEEPMIND AS THE MOST POLEWARD SOLUTION 
AND THE GEFS ENSEMBLE MEAN BEING THE MOST EQUATORWARD SOLUTION. THE 
MAJORITY OF AI-BASED MODELS CONTINUE TO MAKE UP THE NORTHERN SIDE OF 
THE GUIDANCE PACKAGE, WHILE PHYSICS-BASED MODELS AS WELL AS THE AI 
GEFS ENSEMBLE MEAN FAVOR THE SOUTHERN SIDE. ENSEMBLE MODEL ANALYSIS 
REFLECTS THIS SPREAD, WITH PHYSICS-BASED MODEL MEMBERS CONTINUING TO 
FAVOR A FARTHER SOUTH TRACK, WHILE AI- BASED MODELS HEDGE FARTHER 
NORTH, INCREASING THE UNCERTAINTY NEAR THE END OF THE FORECAST PERIOD. 
THE OFFICIAL JTWC FORECAST TRACK IS PLACED WITH HIGH CONFIDENCE OUT TO 
TAU 72 AND MEDIUM CONFIDENCE THEREAFTER, CLOSELY IN LINE WITH THE 
MULTI-MODEL AND AI CONSENSUS, HEDGED SLIGHTLY 
CLOSER TO THE AI CONSENSUS IN TAUS 96 AND 120. MODEL INTENSITY 
GUIDANCE REMAINS IN GOOD AGREEMENT ON A SLIGHT INTENSIFICATION OR 
PLATEAU OUT TO TAUS 60 TO 72, WITH THE EXCEPTION OF THE LOW END 
OUTLIERS OF COAMPS-TC (NAVGEM BASED) AND GFS. NOTABLY, HAFS-A IS NOW 
BELOW THE MULTI-MODEL CONSENSUS BEYOND TAU 12 WHILE BOTH GOOGLE 
DEEPMIND MODELS MAINTAIN PEAKS OF 145-150 KTS. AFTER TAU 72, ALL 
MODELS DEPICT THE STEADY WEAKENING TREND FOR THE REMAINDER OF THE 
FORECAST PERIOD. THE HAFS-A MODEL FIELDS PREDICT ANOTHER ERC TO OCCUR 
BETWEEN TAUS 60 AND 96 AND A STEEPER DECLINE IN INTENSITY ONCE IT 
BEGINS. THE OFFICIAL JTWC FORECAST INTENSITY IS ASSESSED WITH MEDIUM 
CONFIDENCE OUT TO TAU 72 DUE TO THE UNCERTAINTIES DISCUSSED ABOVE AND 
LOW CONFIDENCE THEREAFTER, CLOSELY IN LINE WITH THE OPERATIONAL GOOGLE 
DEEPMIND AND SLIGHTLY ABOVE, BUT REFLECTING THE SHAPE OF THE MULTI-
MODEL CONSENSUS.

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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