WDPN33 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING 
NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 34.6N 142.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 153 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
11W (NEPARTAK) REMAINS ASSESSED AS A SUBTROPICAL STORM. ANIMATED
ENHANCED INFRARED (EIR) AND WATER VAPOR IMAGERY SHOWS THAT NEPARTAK
IS CENTERED BENEATH A STRONG UPPER-LEVEL LOW WITH DRY AIR ADVECTING
AROUND THE SYSTEM. OVER THE PAST SIX HOURS, THE SYSTEM DIPPED
WEST-SOUTHWESTWARD AND CONSOLIDATED WITH A MORE SYMMETRIC, DEFINED
LOW-LEVEL CIRCULATION INDICATED IN EIR AND A 261911Z F-18 NIGHT-TIME 
VISIBLE IMAGE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH 
CONFIDENCE. DUE TO THE SHORT-LIVED WEST-SOUTHWESTWARD TRACK,
THE 261800Z CENTER POSITION WAS RELOCATED ABOUT 75NM SOUTHWEST OF
THE EXPECTED POSITION. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED
WITH HIGH CONFIDENCE BASED ON RECENT ASCAT DATA AS WELL AS THE PGTW
SUBTROPICAL FIX (35-40 KNOTS) AND THE LATEST SATCON ESTIMATE.

INITIAL WIND RADII BASIS: PERSISTENCE 

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: 38 KTS AT 261623Z
   CIMSS ADT: 25 KTS AT 261730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK WESTWARD

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: AFTER TRACKING WEST-SOUTHWESTWARD, 11W HAS
BECOME QUASI-STATIONARY BUT IS FORECAST TO ACCELERATE NORTH-
NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF A NORTH-SOUTH
ORIENTED STR. SLIGHT WEAKENING IS EXPECTED AS THE SUBTROPICAL STORM
NEARS THE COAST OF JAPAN. AFTER TAU 24, 11W WILL TURN NORTHWESTWARD
TO WEST-NORTHWESTWARD AS STEERING TRANSITIONS TO AN EXTENSION OF
THE STR POSITIONED TO THE NORTH. GRADUAL WEAKENING WILL CONTINUE AS
THE SYSTEM CROSSES THE JAPAN ALPS. AS IT 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. 11W SHOULD DISSIPATE BY TAU 72.


MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE SUPPORTS THE JTWC TRACK
FORECAST WITH MEDIUM 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: MEDIUM
   INTENSITY 0 - 72 HR: HIGH//
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