WDPN31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (BAVI) WARNING NR 033//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.3N 129.9E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 506 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE
CONTINUATION OF A WEAKENING TREND AS AN EYEWALL REPLACEMENT CYCLE
(ERC) CAUSES DEGRADATION OF THE INNER CORE. THE EYE HAS BEGUN TO
FILL WITH CLOUD AND THE CENTRAL CONVECTIVE STRUCTURES HAVE BECOME MORE
RAGGED. A DOUBLE EYEWALL STRUCTURE IS PRESENT WITH AN EARLIER
082114Z RCM-1 SAR PASS SHOWING WIND MAXIMA RINGS OF 20 NM AND 55 NM
RADII, RESPECTIVELY. THE OUTER EYEWALL CONTRACTED ABOUT 15 NM
RELATIVE TO THE SAR PASS FROM 12 HOURS PRIOR, AND THE OUTER WIND
MAXIMUM IS NOW THE STRONGER OF THE TWO, INDICATING THAT THE ERC IS
PROGRESSING. MODERATE NORTHEASTERLY SHEAR CONTINUES TO PERIODICALLY
EXACERBATE EROSION OF INNER CORE CONVECTION IN THE NORTHERN
SEMICIRCLE. THE INITIAL INTENSITY IS LOWERED TO 110 KT BASED ON A
BLEND OF AGENCY DVORAK AND OBJECTIVE SATELLITE-BASED INTENSITY
ESTIMATES, COMBINED WITH THE AFOREMENTIONED SAR DATA. TYPHOON 09W
(BAVI) REMAINS A GARGANTUAN TYPHOON, WITH A WIND FIELD SIZE RANKING
IN THE TOP 3 PERCENT OF ALL WESTERN PACIFIC TYPHOONS OF THE PAST
DECADE.

INITIAL WIND RADII BASIS: PERSISTENCE

CURRENT STEERING MECHANISM: COMBINED INFLUENCE OF STR TO THE
NORTHEAST AND BUILDING DEEP-LAYER RIDGE SOUTH OF JAPAN

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T6.0 - 115 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 94 KTS AT 082330Z
   CIMSS AIDT: 92 KTS AT 082330Z
   CIMSS D-PRINT: 110 KTS AT 082350Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON 09W (BAVI) IS TURNING NORTHWESTWARD
AROUND THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE TO THE
NORTHEAST AND A BUILDING DEEP-LAYER RIDGE SOUTH OF JAPAN. THIS
MOTION IS EXPECTED TO CONTINUE OVER THE NEXT 72 HOURS, TAKING BAVI
CLOSE TO ISHIGAKIJIMA, JAPAN BETWEEN 36 AND 48 HOURS, AND THEN INTO
EASTERN CHINA AFTER 60 HOURS. WHILE INLAND OVER CHINA, A TURN
NORTHWARD AND THEN POTENTIALLY NORTHEASTWARD IS EXPECTED AS THE
STORM APPROACHES THE MID-LATITUDE WESTERLIES. REGARDING THE
INTENSITY FORECAST, THERE IS SOME SHORT-TERM UNCERTAINTY WHILE THE
ONGOING EYEWALL REPLACEMENT CYCLE (ERC) PROCEEDS, CREATING A
TUMULTUOUS INNER CORE STRUCTURE AS THE STORM'S KINETIC ENERGY
PROFILE MORPHS. BAVI'S MAXIMUM WINDS ARE EXPECTED TO GRADUALLY
DECREASE IN THE NEAR-TERM TO AROUND 100 KT ON APPROACH TO
ISHIGAKIJIMA. PRESUMING THE ERC COMPLETES, A RECOVERY OF MAXIMUM
WINDS OFTEN FOLLOWS, BUT WITH OCEAN HEAT CONTENT VALUES EXPECTED TO
FALL STEADILY DURING THIS PERIOD, SIGNIFICANT REINTENSIFICATION IS
NOT EXPECTED. HOWEVER, SOME SHORT-TERM FLUCTUATIONS IN INTENSITY,
BOTH UP AND DOWN, MAY OCCUR DUE TO THE EFFECTS OF THE ERC PROCESS.
REGARDLESS OF THE MAXIMUM WINDS IN THE EYEWALL, THE STORM'S MASSIVE
GALE-FORCE WIND FIELD IS EXPECTED TO SPAN FROM SOUTHERN TAIWAN TO
OKINAWA AS BAVI ENTERS THE EAST CHINA SEA. RAPID WEAKENING AND
EVENTUAL DISSIPATION IS EXPECTED FOLLOWING LANDFALL IN CHINA AFTER
TAU 60, THOUGH ELEVATED WINDS MAY PERSIST ALONG THE CHINESE
COASTLINE IN THE EASTERN SEMICIRCLE OF THE REMNANTS.

MODEL DISCUSSION: DYNAMICAL TRACK MODEL GUIDANCE REMAINS SOMEWHAT
SPLIT, WITH PHYSICS-BASED MODELS CLOSER TO TAIWAN AND AI-BASED
MODELS CLOSER TO ISHIGAKIJIMA. HOWEVER, THE GUIDANCE ENVELOPE
REMAINS RELATIVELY TIGHT. THE JTWC TRACK FORECAST IS CLOSE TO A
BLEND OF THE PHYSICS-BASED AND AI-BASED GUIDANCE PACKAGES, AND HAS
SHIFTED SLIGHTLY TO THE RIGHT (NORTHEAST) RELATIVE TO THE PREVIOUS
FORECAST. THE JTWC INTENSITY FORECAST IS SLIGHTLY ABOVE THE
MULTI-MODEL CONSENSUS. MOST INTENSITY GUIDANCE MEMBERS ARE IN GOOD
AGREEMENT ON THE GRADUAL DOWNWARD TREND IN INTENSITY PRIOR TO
LANDFALL IN CHINA.

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