WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (LAN) WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.1N 140.8E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 376 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
MEDIUM-SIZED SYMMETRICAL CYCLONE THAT HAS MOSTLY MAINTAINED ITS 
OVERALL CONVECTIVE AND WRAP STRUCTURE, ALBEIT WITH AN ENLARGED 60-NM
BANDING EYE, EXPOSING A DEFINED LOW LEVEL CIRCULATION CENTER
(LLCC). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON 
THE EXPOSED LLCC FEATURE. THE INITIAL INTENSITY OF 80KTS IS BASED ON 
AN OVERALL ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND 
REFLECTS THE SLIGHT 6-HR DETERIORATION. ANALYSIS INDICATES A 
MARGINALLY FAVORABLE ENVIRONMENT WITH LOW VWS AND MODERATE OUTFLOW 
OFFSET BY LOCALIZED LOW SST AND OHC VALUES DUE TO OCEANIC UPWELLING 
AND DRY AIR INTRUSION.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 82 KTS AT 121130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR INTRUSION WRAPPING IN FROM THE NORTHWEST.


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 LAN WILL CONTINUE ON ITS CURRENT TRACK
TOWARD CENTRAL HONSHU, JAPAN. AFTER TAU 48, IT WILL TRACK MORE
NORTHWARD AS THE STR RECEDES IN RESPONSE TO A MID-LATITUDE TROUGH
APPROACHING FROM THE NORTHWEST, MAKE LANDFALL NEAR MINAMISE AROUND
TAU 60, CREST THE STR AXIS BY TAU 72, EXIT INTO THE SEA OF JAPAN 
(SOJ), THEN ACCELERATE NORTHEASTWARD ON THE POLEWARD SIDE OF THE STR. 
THE MARGINAL ENVIRONMENT WILL SUSTAIN THE CURRENT INTENSITY OF 80KTS 
UP TO TAU 24; AFTERWARD, INCREASING VWS, DRY AIR INTRUSION, THEN LAND 
INTERACTION WILL REDUCE IT TO 50KTS BY TAU 72. DESPITE THE RELATIVELY 
WARM SST IN THE SOJ, INCREASING VWS, THEN INTERACTION WITH THE 
BAROCLINIC ZONE AS TY 07W BEGINS EXTRA-TROPICAL TRANSITION AROUND TAU 
96 WILL GRADUALLY ERODE IT TO A 40-KT COLD CORE LOW BY TAU 120.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY GOOD AGREEMENT WITH
A GRADUAL AND EVEN SPREAD TO JUST 176NM BY TAU 72, LENDING HIGH
CONFIDENCE TO THIS PORTION OF THE JTWC TRACK FORECAST. AFTERWARD,
THE MODELS SPREAD OUT TO 320NM ACROSS AND NOTICEABLE ALONG TRACK
DIFFERENCES BY TAU 120, LENDING MEDIUM CONFIDENCE TO THE EXTENDED
PORTION OF THE TRACK FORECAST. THERE IS MEDIUM CONFIDENCE IN THE
JTWC INTENSITY FORECAST UP TO TAU 72 THEN LOW AFTERWARD DUE TO
VARIABILITY INHERENT WITH EXTRA-TROPICAL TRANSITION.


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