WDPN31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 01W (EWINIAR) WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9N 123.9E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 616 NM SOUTH-SOUTHWEST OF KADENA AB,
OKINAWA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
LOW-LEVEL CIRCULATION CENTER PARTIALLY OBSCURED BY FLARING
CONVECTION DISPLACED TO THE SOUTHEAST BY MODERATE TO STRONG
VERTICAL WIND SHEAR (VWS) THAT HAS CONTINUED TO ERODE THE VERTICAL
STRUCTURE OF TYPHOON 01W OVER THE LAST 12 HOURS. A 270945Z SSMIS
IMAGE DEPICTS THE EXPOSED NORTHWESTERN QUADRANT OF THE ASYMMETRIC
LOW-LEVEL STRUCTURE WITH CONVECTIVE BANDING TO THE SOUTHEAST. THE
INITIAL POSITION WAS PLACED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED EIR AND MICROWAVE IMAGERY. THE INITIAL INTENSITY OF
85 KTS WAS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY AND
OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 69 KTS AT 271130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE NEAR- TO MEDIUM-TERM INTENSITY
FORECAST HAS DECREASED SINCE THE LAST FORECAST CYCLE DUE TO
PERSISTENT, MODERATE VERTICAL WIND SHEAR.

FORECAST DISCUSSION: TY 01W WILL TRACK NORTHEASTWARD UNDER THE
STEERING INFLUENCE OF A STR POSITIONED TO THE EAST. THE SYSTEM WILL
CONTINUE TO BE IMPACTED BY MODERATE VERTICAL WIND SHEAR (VWS)
ASSOCIATED WITH A SHORT-WAVE UPPER-LEVEL TROUGH TO THE NORTHWEST
THROUGH TAU 36. ALTHOUGH FURTHER WEAKENING IS EXPECTED EARLY ON
DUE TO PERSISTENT SHEAR, MODERATE POLEWARD OUTFLOW AND PASSAGE OVER
VERY WARM WATER WILL MITIGATE THE WEAKENING TREND. THE SHORT-WAVE
TROUGH IS EXPECTED TO GRADUALLY PULL AWAY FROM TY 01W, REDUCING VWS
FOR A BRIEF WINDOW BETWEEN TAU 36 AND TAU 72, AFTER WHICH THE
SYSTEM WILL BEGIN TO MERGE WITH A MID-LATITUDE TROUGH. DESPITE THE
DECREASE IN VWS, WEAKENING WILL CONTINUE AS THE STORM MOVES OVER
COOLER WATER, PARTICULARLY NORTH OF 26N. BY TAU 72, TY 01W WILL
START TO MERGE WITH A MID-LATITUDE TROUGH. ASSOCIATED HIGH VWS IS
EXPECTED TO BEGIN TO DECAPITATE THE SYSTEM AT THE MID-LEVELS,
CAUSING THE VORTEX TO SHALLOW AS IT BEGINS EXTRATROPICAL
TRANSITION. THE INTENSITY FORECAST IS SIGNIFICANTLY WEAKER IN THE
EARLY TAUS THAN THE PREVIOUS FORECAST DUE TO STRONGER THAN
PREVIOUSLY EXPECTED VWS.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT THAT TY 01W WILL CONTINUE TO BE STEERED NORTHEASTWARD FOR
THE REMAINDER OF THE FORECAST. A FEW DETERMINISTIC AND ENSEMBLE
MODEL SOLUTIONS INDICATE THAT THE SYSTEM CENTER COULD TRACK
SLIGHTLY NORTH OF THE MULTI-MODEL CONSENSUS AND THE CLOSELY ALIGNED
JTWC FORECAST, BRINGING IT SLIGHTLY CLOSER TO MAINLAND JAPAN, DUE
TO VARYING REPRESENTATIONS OF STORM INTERACTION WITH THE
UPPER-LEVEL TROUGH DURING EXTRATROPICAL TRANSITION. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT THAT WEAKENING WILL OCCUR THROUGH THE
END OF THE FORECAST. HAFS-A, HWRF, AND NAVGEM-BASED COAMPS-TC
SIGNAL SLIGHT INTENSIFICATION OVER THE NEXT 24 HOURS, BUT JTWC
SHIPS GUIDANCE, GFS, AND GFS-BASED COAMPS-TC GUIDANCE FORECASTS
CONSISTENT WEAKENING THROUGH TAU 120. THE JTWC INTENSITY FORECAST
ALIGNS CLOSELY TO THE LOWER MODEL SOLUTIONS ACCOUNTING FOR THE
CURRENT MARGINALLY UNFAVORABLE STATE OF THE ENVIRONMENT. THE SYSTEM
IS EXPECTED TO MAINTAIN TROPICAL STORM EQUIVALENTS INTENSITY DURING
EXTRATROPICAL TRANSITION DUE TO FAVORABLE BAROCLINIC INTERACTION
WITH THE MID-LATITUDE TROUGH.

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