WDPN31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (BAVI) WARNING NR 032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.6N 130.8E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 559 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
09W (BAVI) WITH A DEGRADING INNER CORE STRUCTURE, WITH THE EYE
TEMPERATURE HAVING COOLED ABOUT 8 DEGREES CELSIUS DURING THE PAST
SIX HOURS, AND THE SURROUNDING COLD RING HAVING WARMED ABOUT 10
DEGREES CELSIUS. A NEW EYEWALL REPLACEMENT CYCLE APPEARS TO BE
UNDERWAY AND MAY EXPLAIN SOME OF THIS DEGRADATION. A DOUBLE WIND
MAX STRUCTURE IS OBSERVED IN EARLIER 080910Z SAR DATA, WITH
CONCENTRIC MAX WIND BANDS AT APPROXIMATELY 20 NM AND 70 NM RADII
FROM THE CENTER OF THE EYE. MODERATE NORTHEASTERLY SHEAR IS ALSO
PUSHING DRY AIR INTO THE NORTHERN SEMICIRCLE, CONTRIBUTING TO
INTERMITTENT EROSION OF THE EYEWALL AND FORMATIVE OUTER EYEWALL IN
EIR IMAGERY. THE INITIAL INTENSITY IS LOWERED TO 115 KT BASED ON A
BLEND OF AGENCY DVORAK AND OBJECT SATELLITE-BASED INTENSITY
ESTIMATES. 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 EAST
AND DEEP-LAYER RIDGE SOUTHWEST OF JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T6.5 - 127 KTS
   CIMSS SATCON: 120 KTS AT 1750Z
   CIMSS ADT: 99 KTS AT 1800Z
   CIMSS AIDT: 100 KTS AT 1800Z
   CIMSS D-MINT: 115 KTS AT 081655Z
   CIMSS D-PRINT: 115 KTS AT 081750Z

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

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) WILL TRACK NORTHWESTWARD AS
A BUILDING DEEP-LAYER RIDGE JUST SOUTH OF JAPAN BECOMES THE PRIMARY
STEERING INFLUENCE. THIS TRACK WILL CARRY BAVI INTO THE VICINITY OF
ISHIGAKIJIMA AND TAIWAN IN ABOUT 48 HOURS AS THE STORM ROUNDS THE
WESTERN PERIPHERY OF THE RIDGE, ULTIMATELY MAKING LANDFALL IN
SOUTHEASTERN CHINA JUST BEFORE TAU 72. SOME MODEL SPREAD REMAINS IN
THE PRECISE TRACK NEAR NORTHERN TAIWAN AND THE SOUTHWESTERN
JAPANESE ISLANDS, WITH PHYSICS-BASED MODELS TENDING TO TAKE BAVI
CLOSER TO OR OVER TAIWAN, AND AI-BASED MODELS CLOSER TO
ISHIGAKIJIMA AND OFFSHORE OF TAIWAN. THE JTWC TRACK FORECAST
CONTINUES TO SHOOT BETWEEN THESE TWO GROUPINGS, LEANING A LITTLE
CLOSER TO THE AI-BASED GUIDANCE. AS FOR THE INTENSITY FORECAST, THE
TYPHOON APPEARS TO BE UNDERGOING ANOTHER EYEWALL REPLACEMENT CYCLE
(ERC), WHICH IS LIKELY TO BUMP DOWN THE MAXIMUM WINDS SHORT-TERM.
IT IS UNCLEAR IF THIS ERC WILL EVER CLEANLY COMPLETE, GIVEN THE
STORM'S EXCEPTIONAL SIZE AND THE FACT IT IS GAINING LATITUDE,
MAKING THE VORTEX MORE INERTIALLY STABLE. ADDITIONALLY, OCEAN HEAT
CONTENT VALUES BENEATH THE STORM ARE NOW DECREASING FROM THEIR
PREVIOUS VALUES OF OVER 100 KJ PER SQUARE CENTIMETER, NOW LESS THAN
75, AND EXPECTED TO DECLINE TO AS LOW AS 20 BY 48 HOURS. THIS WILL
GRADUALLY LOWER THE MAXIMUM POSSIBLE INTENSITY CEILING FOR THE
TYPHOON OVER TIME AS THE MASSIVE WIND FIELD BEGINS DYNAMICALLY
COOLING THE SEA SURFACE TO A GREATER EXTENT. THE JTWC INTENSITY
FORECAST IS SLIGHTLY LOWER THAN THE PREVIOUS FORECAST, EXPECTING A
GRADUAL DECLINE TO AROUND 100 KT IN 48 HOURS, THEN WEAKENING MORE
QUICKLY AS THE TYPHOON INTERACTS WITH THE TERRAIN OF TAIWAN AND
CHINA. AFTER LANDFALL, RAPID DISSIPATION IS EXPECTED AS THE STORM
TRACKS INLAND AND TURNS NORTHWARD OVER EASTERN CHINA.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS LAID CLOSE TO A BLEND
OF THE PHYSICS-BASED AND AI-BASED MODEL GROUPINGS, AND WITH HIGH
CONFIDENCE THROUGH TAU 72. THE JTWC INTENSITY FORECAST IS SLIGHTLY
ABOVE THE MULTI-MODEL CONSENSUS AND PLACED WITH MEDIUM CONFIDENCE.
MOST INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON THE GRADUAL
WEAKENING TREND FOR THE FIRST 48 HOURS, THEN MORE RAPID WEAKENING
THEREAFTER.

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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