WDPN31 PGTW 301500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (EWINIAR) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.0N 136.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 348 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 01W (EWINIAR) CONTINUES TO SCURRY OFF TO THE
NORTHEAST ALONG THE WEST SIDE OF THE SUBTROPICAL RIDGE (STR) TO THE
EAST. AUTOMATED PHASE CLASSIFICATION INDICATES THAT THE SYSTEM HAS
NEARLY COMPLETED TRANSITION TO A SUBTROPICAL LOW, WITH THE VORTEX
HAVING DECOUPLED AND MOVED OVER RELATIVELY COOL WATERS (24-25C),
INTERACTION WITH THE 500MB MID-LATITUDE TROUGH AND ENTRAINMENT OF A
SIGNIFICANT AMOUNT OF DRY AIR FROM THE WEST. THE SUBTROPICAL PHASE
WILL BE SHORT-LIVED AND THE TRANSITION SCENARIO WILL BE DISCUSSED
IN MORE DETAIL BELOW. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC), WITH VERY DRY MID-LEVEL AIR CAPPING ANY CHANCE OF
CONVECTIVE DEVELOPMENT. 301132Z ASCAT-C AND 301217Z ASCAT-B
SCATTEROMETER PASSES SHOWED A WELL-DEFINED, BUT SLIGHTLY ELONGATED,
LLCC WITH MAXIMUM WINDS OF 35-40 KNOTS. TAKING INTO ACCOUNT THE
LOW-BIAS IN THIS RANGE OF WINDSPEEDS, THE ACTUAL MAXIMUM INTENSITY
IS LIKELY AROUND 45 KNOTS, WITH THE MAXIMUM EXTENT OF THE
GALE-FORCE WINDS IN THE SOUTHEASTERN QUADRANT. THE INITIAL POSITION
AND INTENSITY WERE SET WITH HIGH CONFIDENCE BASED ON THE ASCAT
DATA. ANALYSIS REVEALS AN UNFAVORABLE ENVIRONMENT, WITH HIGH VWS,
COOL SSTS, SIGNIFICANT DRY MID-LEVEL AIR NO SIGNIFICANT OUTFLOW AS
THE VORTEX IS LIMITED IN VERTICAL EXTENT TO BELOW 700MB. THE TRACK
OVER THE PAST SIX HOURS HAS TURNED A BIT MORE NORTH-NORTHEAST VICE
STRAIGHT NORTHEAST, AS THE LOW-LEVEL STEERING FLOW IS ORIENTED MORE
NORTH-SOUTH THAN THE DEEP-LAYER MEAN FLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A LOW- TO
MID-LEVEL STR. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 45 KTS AT 301200Z
   CIMSS ADT: 26 KTS AT 301300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 24-25 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: SIGNIFICANT MID-LEVEL DRY AIR. 

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: TS 01W WILL CONTINUE TO TRACK GENERALLY
NORTH-NORTHEASTWARD THROUGH THE NEXT 12 HOURS, ALONG THE SLIGHTLY
MORE NORTH-SOUTH ORIENTED LOW- TO MID-LEVEL FLOW ON THE WEST SIDE
OF THE STR TO THE EAST. THE LOW-LEVEL FLOW PATTERN IS EXPECTED TO
SHIFT TO A MORE NORTHEAST-SOUTHWEST AXIS AFTER TAU 12, WHICH WILL
ALLOW THE SYSTEM TO RESUME A MORE NORTHEASTWARD TRACK THROUGH THE
END OF THE FORECAST PERIOD. CPA TO YOKOSUKA HAS DECREASED BY ABOUT
40NM HOWEVER, THE RECENT SCATTEROMETER DATA PROVIDES HIGH
CONFIDENCE ON THE SHAPE OF THE WIND FIELD, WHICH PROVIDES GOOD
CONFIDENCE IN THE EXPECTATION THAT THE GALE-FORCE WINDS WILL REMAIN
OFFSHORE THE TOKYO WAN. WHILE THE SYSTEM IS LIKELY SUBTROPICAL AT
THIS POINT, THIS PHASE OF THE LIFE CYCLE WILL BE VERY SHORT-LIVED.
IN FACT, EXTRATROPICAL TRANSITION (ETT) IS EXPECTED TO BEGIN
SHORTLY AS THE SYSTEM WORKS UNDER AN UPPER-LEVEL TROUGH AND JET MAX
AND BEGINS TO INTERACT WITH THE BAROCLINIC ZONE LURKING A COUPLE
HUNDRED MILES TO THE NORTH. ETT COMPLETION IS EXPECTED WITHIN THE
NEXT 24 HOURS AS THE SYSTEM MOVES NORTHEAST INTO THE OPEN WATERS OF
THE NORTH PACIFIC. WHILE THE SYSTEM IS CLEARLY NO LONGER TROPICAL
IN NATURE, THE WIND FIELD WILL TAKE TIME TO SPIN DOWN AND ONCE IT
COMPLETES ETT, WILL ACTUALLY BEGIN TO INTENSIFY AGAIN DUE TO
BAROCLINIC FORCING. HENCE THE FORECAST CALLS FOR THE SYSTEM TO
MAINTAIN 45 KNOT INTENSITY THROUGH THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE REMAINS
IN TIGHT AGREEMENT, WITH MINIMAL ALONG- OR CROSS-TRACK SPREAD.
HOWEVER, IN LIGHT OF THE RECENT SHIFT TO A SLIGHTLY MORE
NORTH-NORTHEASTWARD TRACK OVER THE PAST SIX HOURS, THE JTWC
FORECAST LIES ON THE EXTREME NORTHERN EDGE OF THE GUIDANCE ENVELOPE
THROUGH THE FORECAST PERIOD. ENSEMBLE SPREAD REMAINS TIGHT BUT A
COUPLE MEMBERS OF THE ECENS DO DRIFT A BIT CLOSER TO JAPAN THAN THE
REMAINDER OF THE GUIDANCE. CONFIDENCE IN THE TRACK FORECAST REMAINS
HIGH, THOUGH A SLIGHTLY CLOSER CPA TO YOKOSUKA CANNOT BE RULED OUT
AT THIS TIME. INTENSITY GUIDANCE IS MIXED, WITH THE GFS, HWRF AND
HAFS-A SHOWING A FLAT INTENSITY TREND THROUGH THE FORECAST PERIOD,
FOLLOWED BY INTENSIFICATION AFTER ETT. THE REMAINDER OF THE
GUIDANCE SHOWS A DRAMATIC WEAKENING TREND, DECREASING THE INTENSITY
TO JUST 15 KNOTS BY TAU 36. THE JTWC FORECAST ALIGNS WELL WITH THE
GFS, HWRF AND HAFS-A WITH HIGH CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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