WDPN31 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (ONE)         
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.9N 121.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 825 NM SOUTH-SOUTHWEST OF KADENA AB,
OKINAWA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 9 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LARGE
OBLONG CENTRAL DENSE OVERCAST FEATURE OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC). HOWEVER, ANIMATED RADAR IMAGERY SHOWS
CONVECTIVE BANDING WRAPPING TIGHTLY INTO A WELL-DEFINED LLCC, WHICH
SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY OF 35 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
PGTW DVORAK ESTIMATE, WHICH ALIGNS CLOSER TO THE RADAR-DERIVED
POSITION. SURFACE WIND OBSERVATIONS IN THE REGION ARE
UNREALISTICALLY TOO LOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) POSITIONED TO THE
NORTH AND NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: ROBUST POLEWARD OUTFLOW CHANNEL ENHANCED BY A
                  DEEP UPPER-LEVEL TROUGH OVER SOUTHEASTERN CHINA.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 01W IS FORECAST TO TURN
NORTHWARD WITHIN THE NEXT 12 HOURS AS THE WESTERN EXTENT OF THE STR
CONTINUES TO ERODE DUE TO ENCROACHING WESTERLIES. AFTER TAU 12, THE
STR WILL CONTINUE TO ERODE AND REALIGN IN A SOUTHWESTWARD TO
NORTHEASTWARD ORIENTATION. THIS WILL ALLOW THE SYSTEM TO TRACK
GENERALLY NORTHEASTWARD THROUGH THE FORECAST PERIOD. AS THE SYSTEM
REEMERGES OVER WATER AFTER TAU 12, IT IS EXPECTED TO INTENSIFY
STEADILY UNDER IMPROVED OVERALL ENVIRONMENTAL CONDITIONS, PRIMARILY
DUE TO DECREASED FRICTIONAL EFFECTS. THE PEAK INTENSITY OF 80 KNOTS
IS SLIGHTLY HIGHER THAN THE PREVIOUS WARNING AND WILL OCCUR NEAR
TAU 72 AFTER A TWO-DAY PERIOD OF OPTIMAL ENVIRONMENTAL CONDITIONS.
AFTER TAU 72, THE SYSTEM WILL INTERACT WITH AN UPPER-LEVEL
SUBTROPICAL TROUGH, WITH ABOUT 15 TO 20 KNOTS OF VERTICAL WIND
SHEAR (VWS). VWS IS EXPECTED TO INCREASE QUICKLY TO 40-45 KNOTS BY
TAU 96 AS THE SYSTEM GAINS LATITUDE; THIS WILL LEAD TO SIGNIFICANT
WEAKENING IN THE EXTENDED FORECAST. NEAR TAU 120, THE SYSTEM WILL
BEGIN INTERACTING WITH THE FRONTAL ZONE OVER JAPAN AND WILL
COMMENCE EXTRA-TROPICAL TRANSITION. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT WITH A 90 NM CROSS-TRACK SPREAD AT TAU 72. HOWEVER,
GUIDANCE SPREADS OUT QUICKLY IN THE EXTENDED FORECAST PERIOD, WITH
MAJOR DIFFERENCES IN TRACK AND TRACK SPEEDS. SEVERAL MODELS (AFUI,
UEMI AND EGRI) DIVERGE FROM THE MAIN CLUSTER OF MODELS, WITH A
TRACK CLOSER TO OKINAWA. HOWEVER, THE BETTER MODELS LIKE GFS,
ECMWF, AND JGSM REMAIN CONSISTENT WITH THE PREVIOUS FORECAST TRACK 
AND SUPPORT THE JTWC FORECAST TRACK WITH MEDIUM CONFIDENCE. THE 
251200Z GEFS ENSEMBLE INDICATES A TIGHT CLUSTER OF SOLUTIONS ALONG 
THE JTWC FORECAST TRACK. THE 251200Z ECMWF ENSEMBLE (EPS) DOES SHOW A 
WIDER SPREAD OF SOLUTIONS, WITH SEVEN SOLUTIONS (ROUGHLY 15 PERCENT) 
OVER OR JUST EAST OF OKINAWA; THE LARGE BULK (85 PERCENT) OF
SOLUTIONS, ARE CLUSTERED TIGHTLY NEAR THE JTWC FORECAST TRACK. AS
DEPICTED BY ECMWF, NAVGEM, AND GFS, THE PROBABILITY OF THE SYSTEM
TRACKING CLOSER TO, OR OVER, OKINAWA IS VERY LOW DUE TO THE
PRESENCE OF AN UPPER-LEVEL TROUGH AND WESTERLIES OVER THAT REGION
AROUND 29 MAY. THE JTWC INTENSITY FORECAST IS HEDGED SLIGHTLY HIGHER 
THAN THE JTWC INTENSITY CONSENSUS (ICNW).     

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