WDPN31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (LAN) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.1N 144.6E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 123 NM NORTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM LAN HAS NOT INTENSIFIED VERY MUCH DURING THE PAST
TWELVE HOURS DESPITE GOING THROUGH THE DIRUNAL MAXIMUM PERIOD.
ANIMATED PROXY VIS IMAGERY SHOWS AND OPEN CENTER WITH A
DISCONTINUOUS BUT DEVELOPING EYEWALL. THERE IS A DEARTH OF DEEP
CONVECTION OVER THE NORTHERN SEMICIRCLE BUT THE ABUNDANT DEEP
CONVECTION OVER THE SOUTHWEST QUADRANT IS SHOWING THE EARLY SIGNS
OF WRAPPING INTO THE NORTHERN SEMICIRCLE AND ENCIRCLING THE CORE.
THERE IS SIGNIFICANT DRY AIR ENTRAINMENT WRAPPING IN FROM THE
NORTHWEST EVIDENT IN TOTAL PRECIPITABLE WATER LOOPS AND 700-300MB
MOISTURE ANALYSES. SATELLITE ANIMATION VERIFIES AN ASYMMETRIC
CIRCULATION WITH THE BULK OF THE DEEP CONVECTION OCCURRING OVER THE
SOUTHWEST QUADRANT.  TS 07W IS TRACKING THROUGH A LOW SHEAR
ENVIRONMENT WITH 30-31C SEA SURFACE TEMPERATURES.  ANIMATED WATER
VAPOR IMAGERY SHOWS THE LOW LEVEL CIRCULATION PULLING AWAY FROM
WHAT WAS AN EXCELLENT POLEWARD OUTFLOW CHANNEL, BUT A WEAK
EQUATORWARD CHANNEL PERSISTS. THE SYSTEM IS BEING DRIVEN POLEWARD
BY THE SOUTHWESTERN FLANK OF THE SUBTROPICAL RIDGE. THE RIDGE IS
ANCHORED IN A 595DM 500MB HEIGHT CENTER NEAR 25N 170W, WITH A LONG
EXTENSION THAT CROSSES NORTHERN HONSHU. THAT LONG AND STRONG RIDGE
IS PREVENTING RECURVATURE AND FORCING THE SYSTEM TOWARDS MAINLAND
JAPAN.

INITIAL WIND RADII BASIS: PERSISTENCE FROM A 090817Z SAR PASS.

CURRENT STEERING MECHANISM: THE WESTERN FLANK OF THE SUBTROPICAL
RIDGE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 53 KTS AT 091740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: A BALANCE OF FAVORABLE AND UNFAVORABLE
ENVIRONMENTAL CONDITIONS WILL KEEP TS 07W INTENSIFYING NEAR A
CLIMATOLOGICAL RATE. THE DEEP LAYER STEERING RIDGE TO THE WEST OF
THE SYSTEM WILL FORCE THE SYSTEM TO REMAIN ON A POLEWARD TRACK. 
SUBSTANTIAL DRY AIR UPSTREAM WILL IMPEDE THE SYSTEM FROM SHARP
INTENSIFICATION, BUT SEA SURFACE TEMPERATURES AVERAGING 29C WILL
SUPPORT THE SYSTEM ALMOST TO LANDFALL. THE KUROSHIO CURRENT IS VERY
NEAR THE COAST WITH ONLY A SHORT ZONE OF COOL WATERS PRIOR TO
LANDFALL. VERTICAL WINDSHEAR WILL ALSO REMAIN BELOW 20 KNOTS
THROUGH THE ENTIRE TRACK. DRY AIR AND SUBSIDENCE UNDERNEATH AN
UPPER LEVEL ANTICYCLONE OVER NORTHERN HONSHU WILL RESTRICT OUTFLOW.
 TRACK GUIDANCE THUS FAR HAS BEEN IN GOOD AGREEMENT REGARDING
LANDFALL BETWEEN WAKAYAMA AND CHIBA PREFECTURES, WITH IZU NOW IN
THE CENTER OF THE TRACK. THERE IS GOOD CONFIDENCE THAT THE SYSTEM
WILL MAKE LANDFALL WELL ABOVE TYPHOON STRENGTH BUT BELOW 100 KNOTS
AND IMPACT THE KANTO PLAIN AND YOKOSUKA AREA. 

MODEL DISCUSSION: ALONG TRACK SPREAD INCREASED OVER THE PAST RUN
BUT CROSS TRACK SPREAD IS MINIMAL. THE TRACK IS EXPECTED TO
INCREASINGLY FOCUS IN ON A LAND STRIKE THAT WILL IMPACT THE KANTO
PLAIN. INTENSITY GUIDANCE IS TIGHTER AGREEMENT THAN NORMAL. THE
JTWC TRACK FORECAST STAYS CLOSE TO THE MULTI MODEL CONSENSUS WHILE
FAVORING THE ENSEMBLE MEANS WHILE THE INTENSITY FORECAST FAVORS THE
HAFS AND HWRF GUIDANCE TO STAY A LITTLE ABOVE CONSENSUS. 

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