Advisories

WDPN32 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 29W (CHAMPI) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.8N 140.2E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 258 NM WEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON 
(TY) 29W (CHAMPI) WITH A REBUILDING CENTRAL DENSE OVERCAST OF COOLING 
CLOUD TOPS AND CONTINUED EFFORTS TO REFORM AN EYE. A DEEP CONVECTIVE 
BAND CONTINUES TO WRAP FROM THE NORTHERN SIDE AROUND THE EASTERN 
FLANK. THE IMPROVING SATELLITE PRESENTATION AND IMMINENT EYE FORMATION 
FURTHER SUPPORT THE POSSIBLE COMPLETION OF THE EYEWALL REPLACEMENT 
CYCLE (ERC), ALTHOUGH THERE HAS BEEN NO RECENT MICROWAVE IMAGERY TO 
DEFINITIVELY CONFIRM THIS. ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH 
WARM (29-30 C) SEA SURFACE TEMPERATURES, LOW (10-15 KTS) VERTICAL WIND 
SHEAR (VWS), AND STRONG RADIAL OUTFLOW ALOFT. THE INITIAL POSITION IS 
PLACED WITH HIGH CONFIDENCE BASED ON THE DEVELOPING WARM SPOT IN EIR. 
THE INITIAL INTENSITY IS ASSESSED WITH LOW CONFIDENCE, SLIGHTLY ABOVE 
THE DVORAK AGENCY FIXES AND CIMSS OBJECTIVE ESTIMATES. UNCERTAINTY 
REGARDING THE INITIAL INTENSITY ARISES FROM BOTH THE LACK OF RECENT 
WIND SPEED DATA AS WELL AS THE SHORT-TERM FLUCTUATIONS DUE TO THE ERC.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMBINATION OF THE SOUTHEASTWARD
EXTENSION OF A SUBTROPICAL RIDGE CENTERED TO THE NORTH AND A
SUBTROPICAL RIDGE CENTERED OVER HONG KONG

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS SATCON: 109 KTS AT 181558Z
   CIMSS ADT: 115 KTS AT 181730Z
   CIMSS AIDT: 106 KTS AT 181730Z
   CIMSS D-MINT: 114 KTS AT 181559Z
   CIMSS D-PRINT: 91 KTS AT 181800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TY 29W IS FORECAST TO CONTINUE NORTHWESTWARD
UNDER THE COMBINED STEERING INFLUENCE OF A SOUTHEASTWARD EXTENSION OF 
A SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTH OF THE SYSTEM AND THE 
EASTWARD EXTENSION OF THE STR CENTERED OVER HONG KONG. AT TAU 60, A 
SLOW IN TRACK SPEED IS EXPECTED AS A POLAR TROUGH PROPAGATES OVER THE 
KOREAN PENINSULA, CREATING A WEAKNESS BETWEEN THE STR TO THE NORTH AND 
THE STR CENTERED OVER SOUTHERN CHINA. THE WESTERN STR OVER SOUTHERN 
CHINA IS EXPECTED TO WEAKEN AS A RESULT AND THE NORTHEASTERN STR IS 
EXPECTED TO BECOME THE PRIMARY STEERING INFLUENCE, INCREASING TRACK 
SPEED AGAIN AT TAU 72 AND CAUSING A MORE POLEWARD TURN BY TAU 96 AS 
29W APPROACHES THE STR AXIS. REGARDING INTENSITY, A CONTINUED PERIOD 
OF INTENSIFICATION OUT TO A PEAK OF 135 KTS IS EXPECTED OUT TO TAU 36, 
FOLLOWED BY A PLATEAU UNTIL TAU 60 AS 29W IS BEGINNING TO ENTER AN 
AREA OF HIGHER (100-150 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC), 
AND MAINTAIN LOW VWS AND FAVORABLE OUTFLOW ALOFT. BEYOND TAU 60, A 
STRONGER WEAKENING TREND WILL BEGIN AS OHC LOWERS AND THE SLOW IN 
TRACK SPEED WILL ENHANCE THE UPWELLING OF COOLER SSTS. THERE REMAINS
UNCERTAINTY IN THE SHORT TERM FORECAST AS ADDITIONAL ERCS ARE 
POSSIBLE, CAUSING FLUCTUATIONS ABOVE OR BELOW THE OFFICIAL INTENSITY 
FORECAST.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT OUT TO
TAU 72 BEFORE BIFURCATING, WITH AI-BASED MODELS DEPICTING A 
RECURVATURE SCENARIO TRACKING IN BETWEEN TAIWAN AND OKINAWA, WHILE 
PHYSICS-BASED MODELS FAVOR A STRAIGHT-RUNNING TRACK OVER CENTRAL 
TAIWAN, RESULTING IN A CROSS-TRACK SPREAD OF 350 NM AND ALONG-TRACK 
SPREAD OF 145 NM BY TAU 120. THE GOOGLE DEEPMIND FNV-3 IS THE MOST 
POLEWARD SOLUTION WHILE GFS IS THE MOST EQUATORWARD, SHOWING A BRIEF 
LANDFALL OVER THE SOUTHERNMOST TIP OF TAIWAN. THE EC AND ECENS MEAN 
SOLUTIONS MAKE UP THE NORTHERNMOST PART OF THE PHYSICS-BASED GROUPING. 
ENSEMBLE MODEL ANALYSIS REVEALS THE PHYSICS-BASED MODELS MODESTLY 
TRENDING MORE NORTHWARD OVER THE PAST FEW CYCLES WITH A HANDFUL OF 
ECENS AND GEFS MEMBERS DEPICTING THE RECURVATURE SCENARIO, HOWEVER THE 
OVERALL SPREAD OF THE EXPERIMENTAL JTWC SUPER ENSEMBLE ENCAPSULATING 
BOTH AI AND PHYSICS BASED ENSEMBLES MAINTAINS A SPREAD REACHING FROM 
THE SOUTHERN TIP OF TAIWAN TO JUST SOUTH OF OKINAWA AT TAU 120. THE 
OFFICIAL JTWC FORECAST IS THUS LAID WITH HIGH CONFIDENCE OUT TO TAU 72 
AND LOW CONFIDENCE THEREAFTER, CLOSELY IN LINE WITH THE MULTI-MODEL 
AND AI CONSENSUS IN THE SHORT TERM AND FAVORING THE MOST EQUATORWARD 
OF THE AI-BASED GROUPING FOR TAU 72 AND BEYOND. MODEL INTENSITY 
GUIDANCE IS IN GOOD AGREEMENT ON A GENERAL PLATEAU OR POSSIBLE 
INTENSIFICATION WITH PEAKS FROM 120-140 KTS OUT TO TAU 60 WITH 
WEAKENING THEREAFTER. HAFS-A AND COAMPS-TC ARE THE HIGHEST MEMBERS, 
BRINGING THE MULTI-MODEL CONSENSUS ABOVE BOTH GOOGLE DEEPMIND 
FORECASTS OUT TO TAU 60. THE FNV-3 GOOGLE MODEL MAKES UP THE LOW END 
OF THE GUIDANCE PACKAGE BY TAU 36, ANTICIPATING A LOWER PEAK AND 
SUBSEQUENT MORE RAPID WEAKENING. THE OFFICIAL JTWC INTENSITY FORECAST 
IS ASSESSED WITH MEDIUM CONFIDENCE OUT TO TAU 72 AND LOW THEREAFTER, 
CLOSELY IN LINE WITH THE MULTI-MODEL CONSENSUS AND SLIGHTLY ABOVE THE 
EXPERIMENTAL WNV-3 GOOGLE MODEL THROUGHOUT.

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