WDPN31 PGTW 120300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (LAN) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.5N 141.8E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 422 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT THE
TYPHOON'S CORE HAS CONTINUED TO DEGRADE OVER THE PAST SIX HOURS,
WITH THE INNER RING OF CLOUD TOPS WARMING SO MUCH THAT A
WELL-DEFINED EYEWALL IS NO LONGER PRESENT. THE COLDEST CLOUD TOPS
ARE NOW OCCURRING IN A CONCENTRIC BAND AT ABOUT 70 NM RADIUS FROM
THE LOW-LEVEL CIRCULATION CENTER (LLCC). AN 112051Z SSMIS MICROWAVE
PASS CONFIRMED THE DEGRADATION OF THE EYEWALL, WITH ONLY ABOUT 40
PERCENT COVERAGE AROUND THE LLCC. OCEANIC UPWELLING IS ALMOST
CERTAINLY TO BLAME FOR THE RECENT WEAKENING TREND, AND LAN
CONTINUES TO MOVE SLOWLY AT 6 KT, ALBEIT A LITTLE FASTER THAN SIX
HOURS AGO. THE INITIAL INTENSITY IS SET AT 85 KT, FOLLOWING FALLING
AGENCY DVORAK ESTIMATES AND OBJECTIVE SATELLITE-DERIVED ESTIMATES,
BUT CONFIDENCE IN THIS ASSESSMENT IS LOWER THAN AVERAGE DUE TO THE
RAPID EVOLUTION OF THE STORM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T5.0 - 90 KTS
   CIMSS ADT: 84 KTS AT 112340Z

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) APPEARS TO HAVE MADE A TURN
WEST-NORTHWESTWARD DURING THE PAST SIX HOURS WHILE SLIGHTLY
ACCELERATING, INDICATING THAT THE SUBTROPICAL RIDGE TO THE
NORTHEAST IS BEGINNING TO BUILD WESTWARD. THIS RIDGE 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 ALONG THE WEST SIDE OF ISE BAY, JAPAN JUST
AFTER 72 HOURS. MODEL SPREAD HAS TIGHTENED AROUND THE LANDFALL POINT
SOMEWHAT SINCE THE PREVIOUS FORECAST, BUT THE ECMWF AND GFS
ENSEMBLE ENVELOPES REMAIN ABOUT 200 NM WIDE AT THE LANDFALL POINT.
THIS IS PRIMARILY DUE TO SOME UNCERTAINTY IN THE STRENGTH AND SHAPE
OF THE SUBTROPICAL RIDGE TO LAN'S NORTHEAST OVER THE NEXT FEW DAYS.
REGARDING THE INTENSITY FORECAST, LAN CONTINUES TO DEGRADE DUE TO
COLD UPWELLING, BUT IS NOW ACCELERATING SLIGHTLY AND WILL MOVE OVER
A WARMER EDDY DURING THE NEXT 24-48 HOURS. SOME STABILIZATION OR
RECOVERY OF THE TYPHOON IS THUS EXPECTED, AND THE JTWC FORECAST
SHOWS A CONSTANT INTENSITY OF 85 KT THROUGH 48 HOURS, THOUGH
SHORT-TERM FLUCTUATIONS MAY OCCUR. SLIGHT WEAKENING TO 75 KT BY 72
HOURS 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 IT COULD REMAIN A TROPICAL STORM 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 AND INTENSITY FORECASTS ARE BOTH
CLOSE TO THE MULTI-MODEL CONSENSUS. BOTH TRACK AND INTENSITY MODEL
SPREAD HAVE NARROWED SOMEWHAT SINCE THE PREVIOUS FORECAST.

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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