WDPN31 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (EWINIAR) WARNING NR 
023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.9N 135.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 432 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH ISOLATED
CONVECTION LIMITED TO THE EASTERN HALF OF THE CIRCULATION. IN THE
BROADER VIEW, THE ANIMATED MSI SHOWS THE WESTERN END OF A
STATIONARY BOUNDARY ABOUT 400NM NORTHEAST OF THE CURRENT POSITION.
ANIMATED WATER VAPOR IMAGERY SUGGESTS AN UPPER-LEVEL TROUGH LIES
JUST WEST OF TS 01W, SUPPORTED BY A SHIFT OF THE 200MB WINDS AT
ROMD FROM WEST TO NORTH OVER THE PAST 12 HOURS. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC
IN THE MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE HIGHER END PGTW DVORAK CURRENT INTENSITY
(CI) VALUES OF T3.5 AND IN LINE WITH THE 0600Z SATCON ESTIMATE OF
50 KNOTS. ANALYSIS REVEALS AN UNFAVORABLE ENVIRONMENT,
CHARACTERIZED BY RELATIVELY COOL (24-25C) SSTS, HIGH VERTICAL WIND
SHEAR (VWS) EXCEEDING 25 KNOTS, STRONG POLEWARD OUTFLOW AND
MID-LEVEL DRY AIR RAPIDLY ENGULFING THE SYSTEM FROM THE WEST. WHILE
OUTFLOW IS STRONG, IT IS RELATIVELY CUT-OFF FROM THE VORTEX, WHICH
HAS NOW COMPLETELY DECOUPLED. MANUAL AND AUTOMATED PHASE
CLASSIFICATION WORKSHEETS INDICATE THE SYSTEM REMAINS TROPICAL BUT
IS RAPIDLY BECOMING MORE SUBTROPICAL IN NATURE AS IT LOSES THE
TROPICAL CHARACTERISTICS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A STRONG
SUBTROPICAL RIDGE (STR) CENTERED THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 50 KTS AT 300600Z
   CIMSS ADT: 34 KTS AT 300600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST. 

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

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) IS RAPIDLY
DISINTEGRATING AS IT RACES NORTHEASTWARD. HIGH VWS HAS TAKEN ITS
TOLL ON THE SYSTEM OVER THE PAST 18 HOURS OR SO, WITH THE VORTEX
NOW COMPLETELY DECOUPLED AND RESTRICTED IN VERTICAL EXTENT TO A
MAXIMUM OF ABOUT 700MB. ABOVE THAT, EXTREMELY DRY AND STABLE AIR IS
FLOWING RAPIDLY EASTWARD OVER TOP OF THE LLCC, IN THE LEE OF A
500MB TROUGH. THE SYSTEM IS FORECAST TO CONTINUE TRACKING
NORTHEASTWARD THROUGH THE DURATION OF THE FORECAST PERIOD, ALONG THE
NORTHWESTERN SIDE OF THE STR ENTRENCHED TO THE EAST. AFTER HAVING
SLOWED DOWN A BIT OVER THE PAST 12 HOURS, TS 01W IS EXPECTED TO
START ACCELERATING AGAIN IN THE NEAR-TERM, THEN REALLY KICK IT INTO
HIGH GEAR AFTER TAU 12, EVENTUALLY REACHING A FORWARD SPEED OF
ABOUT 30 KNOTS BY THE END OF THE FORECAST. WHILE THE SYSTEM IS
FULLY DECOUPLED AND HAS ALREADY LOST NEARLY ALL OF ITS TROPICAL
CHARACTERISTICS, THE LOW-LEVEL VORTEX WILL TAKE TIME TO SPIN DOWN.
ADDITIONALLY, BY THE TIME IT TRANSITIONS TO AN EXTRA-TROPICAL LOW,
IT WILL BEGIN TO REINTENSIFY DUE TO STRONG BAROCLINIC FORCING.
HENCE THE SYSTEM IS NOT EXPECTED TO WEAKEN MUCH OVER THE COURSE OF
THE FORECAST. AS DISCUSSED ABOVE, THE SYSTEM IS ALREADY STARTING TO
TRANSITION TO A SUBTROPICAL LOW, BUT THIS PHASE WILL BE VERY SHORT
LIVED AND THUS IS NOT SPECIFICALLY CALLED OUT IN THE FORECAST.
REGARDLESS OF THE SHORT SUBTROPICAL PHASE, THE SYSTEM WILL QUICKLY
TRANSITION TO A STRONG EXTRA-TROPICAL LOW NO LATER THAN TAU 36, AS
IT BECOMES EMBEDDED UNDER A MID-LATITUDE SHORTWAVE TROUGH AND
ASSOCIATED JET MAX. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE MODEL TRACKERS ARE IN
GOOD AGREEMENT ON THE TRACK, BOTH IN THE ACROSS- AND ALONG-TRACK
ASPECTS, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.
INTENSITY GUIDANCE IS IN MODERATE AGREEMENT, WITH ABOUT 15 KNOTS OF
SPREAD BETWEEN THE OUTLIERS. HOWEVER, THE BULK OF THE GUIDANCE
AGREES WITH THE OVERALL FORECAST PHILOSOPHY, CALLING FOR A SLIGHT
WEAKENING FOLLOWED BY REINTENSIFICATION AFTER THE SYSTEM COMPLETES
ETT. THE JTWC FORECAST LIES ON THE HIGHER END OF THE GUIDANCE
PACKAGE, WITH MEDIUM CONFIDENCE. 

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