WDPN32 PGTW 151500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 08W (EIGHT) WARNING NR
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 36.5N 141.0E
INITIAL INTENSITY: 40 KTS
GEOGRAPHIC REFERENCE: 56 NM NORTH-NORTHEAST OF NARITA AIRPORT
MOVEMENT PAST 6 HOURS: NORTHWARD AT 38 KTS
SIGNIFICANT WAVE HEIGHT: 18 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES A
FURTHER INCREASE IN FORWARD MOTION OF THE LOW-LEVEL CIRCULATION
CENTER (LLCC) ASSOCIATED WITH TROPICAL STORM (TS) 08W. TRANSLATION
SPEED OVER THE LAST 6 HOURS REACHED 38 KTS AND THE LLCC CAN BE SEEN
FULLY EXPOSED AGAIN CLIPPING CAPE INUBO, JAPAN AND APPROACHING THE
FUKUSHIMA PREFECTURE ALONG ITS NORTHWARD TRACK. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE, BASED ON CLEARLY IDENTIFIABLE LLCC.
THE INITIAL INTENSITY IS ALSO ASSESSED AT 40 KTS WITH HIGH CONFIDENCE
BASED ON A 151039Z METOP-B ASCAT, AS WELL AS LATEST SUBJECTIVE DVORAK
ESTIMATES AND OBJECTIVE AUTOMATED INTENSITY ESTIMATES. ENVIRONMENTAL
CONDITIONS ARE BECOMING UNFAVORABLE FOR TROPICAL DEVELOPMENT, DUE TO
INCREASING TERRAIN INTERACTION AND COOL (22-23 C) SEA SURFACE
TEMPERATURES (SST), OFFSET BY LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS)
AND MODERATE EQUATORWARD OUTFLOW.
INITIAL WIND RADII BASIS: A 151039Z METOP-B ASCAT
CURRENT STEERING MECHANISM: STRONG SUBTROPICAL RIDGE (STR) TO THE
EAST-NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T2.0 - 30 KTS
KNES: T2.0 - 30 KTS
CIMSS SATCON: 37 KTS AT 151200Z
CIMSS ADT: 39 KTS AT 151140Z
CIMSS AIDT: 43 KTS AT 151200Z
CIMSS D-PRINT: 28 KTS AT 151230Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
VWS: 10-15 KTS
SST: 22-23 CELSIUS
OUTFLOW: MODERATE EQUATORWARD
OTHER FACTORS: TERRAIN INTERACTION OVER EASTERN HONSHU
ANALYSIS CONFIDENCE:
INITIAL POSITION: HIGH
INITIAL INTENSITY: HIGH
INITIAL WIND RADII: HIGH
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: THE LLCC OF TS 08W IS CURRENTLY VOID OF
CENTRAL CONVECTION AND IS FORECAST TO MAKE A CLOSE APPROACH AND
EVENTUAL LANDFALL OVER THE JAPANESE COASTLINE WITHIN THE NEXT 6
HOURS. THE CURRENT MOTION VECTOR IS STILL DRIVEN BY DEEP-LAYER MEAN
STEERING FLOW ASSOCIATED WITH A BROAD STR TO THE EAST-NORTHEAST,
AHEAD OF A MID-LATITUDE LONGWAVE TROUGH ANCHORED OVER THE KOREAN
PENINSULA. SIMULTANEOUSLY, THE SYSTEM IS RAPIDLY APPROACHING THE
AXIS OF THE RIDGE AND IS FORECAST TO BEGIN TURNING NORTHEASTWARD,
WHEN IT WILL EVENTUALLY BECOME FULLY EMBEDDED IN THE DEEP-LAYER,
WESTERLY FLOW. FULL DISSIPATION IS EXPECTED BETWEEN 24 AND 36
HOURS, BUT CAN OCCUR EARLIER, IF THE VORTEX TRAVELS OVER OR CLOSER
TO LAND. LANDFALL OVER NORTHEASTERN HONSHU IS ANTICIPATED WITHIN
THE NEXT 3-6 HOURS, WITH A SECONDARY LANDFALL OVER SOUTHERN CENTRAL
HOKKAIDO PRIOR TO TAU 12. WIND FIELD ANALYSIS REVEALS THAT THE BULK
OF GALE-FORCE WINDS CONTINUE TO BE CONFINED TO THE EASTERN SEMICIRCLE.
GRADUAL WEAKENING TREND IS EXPECTED TO BEGIN IMMEDIATELY, AS LAND
INTERACTION BEGINS TO DISRUPT THE VORTEX STRUCTURE. ADDITIONALLY, TS
08W WILL BE MOVING INTO AN INCREASINGLY HOSTILE ENVIRONMENT
CHARACTERIZED BY ENHANCED VWS AND RAPIDLY DECREASING SST VALUES.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GENERAL AGREEMENT
THROUGH THE NEAR TERM, ALTHOUGH NOT ALL DYNAMIC MODELS HAVE
ADEQUATELY INITIALIZED THE LLCC STRUCTURE. CROSS-TRACK SPREAD AMONG
ENSEMBLE MEMBERS IS MINIMAL, SUPPORTING HIGH CONFIDENCE IN THE
SHORT-TERM TRACK, BUT THE GUIDANCE ENVELOPE OPENS UP CLOSER TO
DISSIPATION. THUS, THE JTWC OFFICIAL TRACK FORECAST IS ISSUED WITH
MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS CONSISTENT IN INDICATING
ABRUPT WEAKENING DUE TO COMBINED EFFECTS OF STRONG VWS AND SURFACE
FRICTIONAL FORCING ASSOCIATED WITH LAND INTERACTION. DISSIPATION
TIMING REMAINS UNCERTAIN, BUT MOST OF THE MULTI-MODEL CONSENSUS
MEMBERS INDICATE SYSTEM DECAY WITHIN THE 12 TO 24 HOUR TIMEFRAME.
FORECAST CONFIDENCE:
TRACK 0 - 72 HR: MEDIUM
INTENSITY 0 - 72 HR: MEDIUM//
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