WDPN31 PGTW 112100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (LAN) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.2N 142.4E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 448 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A RAPIDLY
DECAYING INNER CORE OF TYPHOON 07W (LAN) OVER THE PAST 12 HOURS.
THE STORM IS STRUGGLING TO CLOSE OFF EVEN A -60 DEGREE CELSIUS COLD
RING AROUND THE EYE. THIS IS LIKELY DUE TO OCEANIC UPWELLING, AS
NCODA OCEAN ANALYSIS SHOWS THAT LAN IS MOVING OVER A LOCAL MINIMUM
IN OCEANIC HEAT CONTENT OF LESS THAN 20 KJ PER SQUARE CENTIMETER,
AND PROCEEDING VERY SLOWLY AT A CURRENT SPEED OF 3 KT AS IT DOES
SO. THE INITIAL INTENSITY IS SET AT 95 KT BASED ON A BLEND OF
FALLING AGENCY DVORAK ESTIMATES AND OBJECTIVE SATELLITE-DERIVED
ESTIMATES, BUT CONFIDENCE IN THIS ASSESSMENT IS LOW DUE TO THE
ONGOING RAPID EVOLUTION OF THE STORM. UPPER-LEVEL OUTFLOW IS
PREDOMINANTLY EQUATORWARD, AND A DEEPLY DRY AIRMASS REMAINS
NORTHWEST OF 07W BETWEEN THE STORM AND MAINLAND JAPAN.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 97 KTS AT 111730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR MASS TO THE NORTHWEST

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: TYPHOON 07W (LAN) IS MOVING AT ITS SLOWEST
FORWARD SPEED SO FAR AS THE SUBTROPICAL RIDGE TO ITS NORTHEAST IS
TEMPORARILY WEAKENED BY AN UPPER-LEVEL LOW CURRENTLY EAST OF JAPAN.
THE RIDGE IS EXPECTED TO BUILD WESTWARD OVER THE NEXT 48 HOURS,
CAUSING A TURN NORTHWESTWARD OR WEST-NORTHWESTWARD AND SLIGHT
ACCELERATION. THIS RIDGE EAST OF JAPAN WILL CONTINUE TO GUIDE THE
TYPHOON AROUND ITS WESTERN PERIPHERY, WITH LAN TURNING NORTHWESTWARD 
AND THEN NORTHWARD AS IT CROSSES HONSHU BETWEEN 72 AND 96 HOURS. A 
WEAK UPPER-LEVEL TROUGH OVER NORTHEASTERN CHINA IS THEN EXPECTED TO 
TURN 07W NORTH-NORTHEASTWARD OVER THE SEA OF JAPAN. THE JTWC TRACK
FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND SHOWS LAN PASSING
OVER ISE BAY, JAPAN AND NAGOYA, JAPAN BETWEEN 72 AND 96 HOURS. 
SIGNIFICANT CROSS-TRACK MODEL SPREAD OF ABOUT 200 NM DOES REMAIN
AROUND THE LANDFALL POINT, MAKING THE EXACT LANDFALL LOCATION
UNCERTAIN. THIS IS PRIMARILY DUE TO FUZZINESS IN THE STRENGTH AND
SHAPE OF THE SUBTROPICAL RIDGE TO LAN'S NORTHEAST OVER THE NEXT FEW
DAYS. DYNAMICAL ENSEMBLES CONTINUE TO SHOW THAT A RELATIVELY WIDE
RANGE OF LANDFALL LOCATIONS IN JAPAN ARE POSSIBLE, WITH IMPACTS AS
FAR WEST AS IWAKUNI OR AS FAR EAST AS YOKOSUKA STILL WITHIN THE
ENVELOPE OF POSSIBILITIES. TURNING TO THE INTENSITY FORECAST, IT IS
CURRENTLY CHALLENGING, AS TYPHOON LAN IS PASSING OVER A PATCH OF
SHALLOW WARM WATER WHICH HAS COOLED BENEATH THE CIRCULATION,
CAUSING ABRUPT WEAKENING. SOME STABILIZATION OR RECOVERY OF THE
TYPHOON IS LIKELY DURING THE 24-48 HOUR PERIOD AS THE STORM MOVES
NEAR AN EDDY OF HIGHER OCEANIC HEAT CONTENT, BUT OVERALL HEAT
CONTENT VALUES WILL REMAIN LOW. THERE IS THUS A HARD CEILING ON
LAN'S INTENSITY PRIOR TO LANDFALL IN JAPAN, BUT THE EXTENT OF
SHORT-TERM WEAKENING IS DIFFICULT TO PREDICT WITH CONFIDENCE. THE
JTWC FORECAST SHOWS WEAKENING TO 85 KT BY 24 HOURS, THEN FLATLINING
THROUGH 48 HOURS DUE TO PRESUMED IMPROVEMENT IN OCEANIC CONDITIONS.
SLIGHT WEAKENING TO 80 KT JUST BEFORE LANDFALL IN JAPAN IS FORECAST
DUE TO THE ONSET OF SOME MID-LEVEL VERTICAL SHEAR AS LAN GETS
CLOSER TO A WEAK UPPER-LEVEL TROUGH OVER THE YELLOW SEA, ALONG WITH
COOLER JAPANESE COASTAL WATERS. UPON CROSSING HONSHU, LAN WILL
ENTER THE SEA OF JAPAN IN ABOUT 96 HOURS, WHERE ITS INTENSITY COULD
REMAIN AROUND 50 KT FOR A TIME, AS WATERS THERE ARE WARM. HOWEVER,
CONTINUED NORTH-NORTHEASTWARD MOTION IS EXPECTED TO BRING LAN INTO
A ZONE OF ELEVATED WIND SHEAR ASSOCIATED WITH THE UPPER-LEVEL
TROUGH OVER NORTHEASTERN CHINA, AND THE ASSOCIATED BAROCLINIC
INTERACTION SHOULD INITIATE EXTRATROPICAL TRANSITION COINCIDENT
WITH STEADY WEAKENING BY 120 HOURS.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS AND IS SIMILAR TO THE PREVIOUS FORECAST. THE
JTWC INTENSITY FORECAST IS HIGHER THAN THE DYNAMICAL GLOBAL MODELS
IN THE SHORT-TERM, BUT LOWER THAN THE HAFS MESOSCALE MODEL THROUGH
48 HOURS DUE TO THE MODEL'S UNREALISTICALLY HIGH DEPICTION OF
TYPHOON LAN'S CURRENT INTENSITY.

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