WDPN31 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (LAN) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.3N 140.0E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 360 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 29 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CLASSIC SIGNATURE OF A TYPHOON WHOSE INNER CORE HAS BEEN HOLLOWED
OUT BY DYNAMIC OCEAN COOLING BENEATH THE STORM CENTER. THE RADIUS
OF MAXIMUM WINDS HAS INCREASED TO AT LEAST 40 NM BASED ON 121213Z
ASCAT-C DATA, CONFIDENT WITH THE LARGE RING OF -60 TO -70 DEGREE
CELSIUS CLOUD TOPS NOW NEARLY ENCIRCLING THE BROAD LLCC. THE
INITIAL INTENSITY IS SET AT 65 KT BASED ON EARLIER 120842Z RCM-1
SAR DATA, WHICH CONFIRMED MORE WEAKENING OF TYPHOON 07W (LAN) THAN
ORIGINALLY ASSESSED. NCODA OCEAN ANALYSIS SHOWS THAT LAN IS NOW
MOVING OUT OF THE AREA OF LOWEST OCEANIC HEAT CONTENT OF LESS THAN
20 KJ PER SQUARE CENTIMETER AND INTO AN AREA OF SLIGHTLY HIGHER
HEAT CONTENT OF NEAR OR ABOVE 30 KJ PER SQUARE CENTIMETER. A DRY
AIR MASS REMAINS ENTRENCHED TO THE WEST OF LAN BUT IS NOT BEING
SIGNIFICANTLY INGESTED INTO THE CORE DUE TO THE LACK OF VERTICAL
SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   CIMSS ADT: 77 KTS AT 121420Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR MASS TO THE WEST

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INTENSITY FORECAST THROUGH THE
FIRST 48-72 HOURS HAS BEEN LOWERED DUE TO THE LOWER ASSESSED
INITIAL INTENSITY.

FORECAST DISCUSSION: TYPHOON 07W (LAN) HAS LOST ITS ORIGINAL INNER
CORE DUE TO DYNAMIC OCEAN COOLING, AND NOW HAS A BROADER CORE RING
OF MAXIMUM WINDS. LAN IS NOW MOVING INTO AN AREA OF SLIGHTLY HIGHER
OCEAN HEAT CONTENT AS IT TRACKS NORTHWESTWARD NEAR THE EASTERN SIDE
OF A DEEP WARM EDDY. THIS WILL LIKELY PREVENT FURTHER WEAKENING,
AND MAY EVEN RESULT IN SLIGHT REINTENSIFICATION OF THE VORTEX AS IT
TRACKS AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE
TOWARDS CENTRAL HONSHU. HOWEVER, THE BROAD NATURE OF THE VORTEX
WILL LIKELY LIMIT THE PACE OF STRENGTHENING, IF ANY. THE JTWC
INTENSITY FORECAST IS ACTUALLY LOWER THAN THE PREVIOUS ONE THROUGH
LANDFALL IN JAPAN, BUT NO LONGER SHOWS FURTHER WEAKENING, AS IT
APPEARS THAT THE MAXIMUM IMPACT OF OCEAN COOLING HAS NOW PASSED.
DYNAMICAL MODELS HAVE BECOME MORE TIGHTLY CLUSTERED AND ARE IN GOOD
AGREEMENT ON THE LANDFALL LOCATION. THE JTWC TRACK FORECAST IS
SLIGHTLY EAST OF THE MULTI-MODEL CONSENSUS, AND SIMILAR TO THE
PREVIOUS FORECAST. MODELS ARE IN GOOD AGREEMENT THAT LAN WILL CROSS
HONSHU BETWEEN 48 AND 72 HOURS, EMERGING OVER THE SEA OF JAPAN AND
TURNING NORTHEASTWARD. INTERACTION WITH UPPER-LEVEL TROUGHING OVER
NORTHEASTERN CHINA AND A COOLER AIR MASS IS EXPECTED TO INITIATE
EXTRATROPICAL TRANSITION DURING THE 96-120 HOUR PERIOD, COMPLETING
BY 120 HOURS AS THE WARM CORE STRUCTURE OF THE STORM DISSOLVES.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS SLIGHTLY TO THE RIGHT
OF THE MULTI-MODEL CONSENSUS. THE JTWC INTENSITY FORECAST IS CLOSE
TO THE MULTI-MODEL CONSENSUS, NOT QUITE AS HIGH AS HAFS-A AND HWRF
DUE TO THEIR REPRESENTATIONS OF THE VORTEX AS SLIGHTLY MORE COMPACT
THAN IT ACTUALLY IS, LEADING TO MORE INTENSIFICATION IN THOSE
MODELS.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: HIGH//
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