Tropical Storm NEPARTAK Advisory mar, 27.07.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING
NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 34.9N 142.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 140 NM EAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
11W (NEPARTAK) REMAINS ASSESSED AS A SUBTROPICAL STORM. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY DEPICTS SHALLOW BANDING WRAPPING
TIGHTLY INTO A FULLY-EXPOSED LOW-LEVEL CIRCULATION CENTER, WHICH
SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. ANIMATED WATER
VAPOR IMAGERY SHOWS THAT NEPARTAK IS CENTERED BENEATH A STRONG
UPPER-LEVEL LOW WITH DRY AIR ADVECTING AROUND THE SYSTEM. AFTER AN
UNEXPECTED, SHORT-LIVED WEST-SOUTHWESTWARD TRACK, 11W HAS
ACCELERATED POLEWARD ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL
RIDGE. ALONG WITH HOURLY RADAR FIXES FROM RJTD, A 262323Z ASCAT-A
BULLSEYE IMAGE ALSO SUPPORTS THE INITIAL POSITION AND INITIAL
INTENSITY OF 45 KTS WITH HIGH CONFIDENCE.
INITIAL WIND RADII BASIS: SCATTEROMETER DATA
CURRENT STEERING MECHANISM: LOW TO MID-LEVEL SUBTROPICAL RIDGE
(STR) TO THE EAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: ST2.5 - 35-40 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS SATCON: 48 KTS AT 262125Z
   CIMSS ADT: 39 KTS AT 262340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK WESTWARD
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: 11W IS FORECAST TO TRACK NORTH-NORTHWESTWARD
THROUGH TAU 24 AS IT MAKES LANDFALL AND TRACKS OVER THE JAPAN ALPS.
SLIGHT WEAKENING IS EXPECTED AS THE SUBTROPICAL STORM TRACKS
OVERLAND. AFTER TAU 24, 11W WILL TURN NORTHWESTWARD TO WEST-
NORTHWESTWARD AS THE STEERING TRANSITIONS TO AN EXTENSION OF THE STR
POSITIONED TO THE NORTH. AS 11W REEMERGES OVER THE EAST SEA, THE
SYSTEM WILL WEAKEN STEADILY DUE TO INCREASING VERTICAL WIND SHEAR
(25 TO 35 KNOTS) ASSOCIATED WITH STRONG NORTHERLY FLOW ALOFT WITH
DISSIPATION EXPECTED BY TAU 72.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE SUPPORTS THE JTWC TRACK
FORECAST WITH HIGH CONFIDENCE AND IS POSITIONED CLOSE TO THE
MULTI-MODEL CONSENSUS. THE TRACK FORECAST IS ALSO SUPPORTED BY THE
261200Z ECMWF ENSEMBLE STRIKE PROBABILITY PRODUCT. THE JTWC
INTENSITY FORECAST IS SUPPORTED BY THE INTENSITY CONSENSUS (ICNW)
WITH HIGH CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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