WDPN31 PGTW 302100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (EWINIAR) WARNING NR
025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.7N 138.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 224 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 21 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED ASYMMETRIC LOW-LEVEL CIRCULATION CENTER (LLCC) AND IS
DEVELOPING A COLD FRONT IN THE SOUTHWEST QUADRANT.  STRONG VERTICAL
WIND SHEAR (VWS) OF 40-45KTS FROM THE NORTHWEST HAS CAUSED THE
VORTEX TO BECOME SHALLOW AND DEEP CONVECTION HAS FULLY SEPARATED
FROM THE LLCC.  EARLIER, THE SYSTEM BRIEFLY WENT THROUGH ITS
SUBTROPICAL PHASE AND IS NOW BECOMING EXTRATROPICAL AS IT BECOMES
EMBEDDED UNDER THE POLAR FRONT JET TO THE NORTH.  A 311712Z AMSR-2
89GHZ IMAGE DEPICTS THE OBLONG LOW-LEVEL CENTER AND PARTIALLY
CAPTURED THE DEVELOPMENT OF THE DEVELOPING COLD FRONT. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED
ANIMATED EIR AND AMSR-2 IMAGE. THE INITIAL INTENSITY OF 45 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE
FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND 311218Z METOP-B
ASCAT IMAGE

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

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 25 KTS AT 301830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 40-45 KTS
   SST: 23-24 CELSIUS

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM (TS) 01W (EWINIAR) WILL
CONTINUE TO BE STEERED NORTHEASTWARD BY A STR TO THE EAST.  AS THE
SYSTEM BECOMES SHALLOWER, THE LOW-LEVEL STR WILL BECOME THE PRIMARY
STEERING MECHANISM BUT THE SYSTEM WILL CONTINUE TRACKING NORTHEAST
AND ACCELERATE INTO THE MID-LATITUDES. TS 01W IS ANTICIPATED TO
REMAIN 45KTS AS IT CONTINUES THROUGH EXTRATROPICAL TRANSITION. TS
EWINIAR SYSTEM WILL COMPLETE EXTRATROPICAL TRANSITION NO LATER THAN
24 HOURS FROM NOW. ONCE EXTRATROPICAL TRANSITION IS COMPLETE, THE
SYSTEM MAY INTENSIFY AS IT MOVE TO TOWARDS THE ALEUTIANS AS A DEEP
MID-LATITUDE STORM SYSTEM.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN STRONG
AGREEMENT THAT THE SYSTEM WILL CONTINUE TO TRACK NORTHEASTWARD ON
THE PERIPHERY OF A STR, WITH A MAXIMUM ALONG-TRACK SPREAD OF 95NM.
THE INTENSITY GUIDANCE IS IN MODERATE AGREEMENT THAT THE STORM WILL
POTENTIALLY WEAKEN OVER THE NEXT 24 HOURS, BUT OVERALL, THE SYSTEM
WILL REINTENSIFY IN THE LONG-TERM DUE TO BAROCLINIC FORCING AND AN
INFLUX OF COLDER CONTINENTAL POLAR AIR SURGING OFF THE CONTINENT.
ENSEMBLE GUIDANCE REFLECTS THE STRONG AGREEMENT OF THE
DETERMINISTIC MODELS, DEPICTING A TIGHT NORTHEASTWARD TRACK.

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