WDPN31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (EWINIAR)     
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.1N 121.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 826 NM SOUTH-SOUTHWEST OF KADENA AB,
                         OKINAWA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 8 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AS DEPICTED IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND 
RECENT MICROWAVE IMAGERY, TROPICAL STORM (TS) 01W UNDERWENT A PERIOD 
OF SIGNIFICANT INTENSIFICATION OVER THE PAST SIX HOURS. EIR SATELLITE 
IMAGERY DEPICTS A COMPACT CENTRAL DENSE OVERCAST FEATURE WITH A 
RAGGED, FORMATIVE EYE. A 252040Z GMI 89 GHZ MICROWAVE IMAGE DEPICTS 
AN IMPRESSIVE, WELL-DEFINED MICROWAVE EYE FEATURE, WHICH ALONG WITH 
ANIMATED RADAR IMAGERY, SUPPORTS THE INITIAL POSITION WITH HIGH 
CONFIDENCE. WITH THE EXCEPTION OF THE FRICTIONAL EFFECTS DUE TO LAND 
INTERACTION, THE ENVIRONMENT IS FAVORABLE WITH RADIAL OUTFLOW AND AN 
ENHANCED POLEWARD CHANNEL. THE INITIAL INTENSITY IS ASSESSED AT 55 
KNOTS BASED ON THE CIMSS ADT AND AIDT ESTIMATES, WHICH ARE CONSISTENT 
WITH THE MICROWAVE EYE STRUCTURE AND DEVELOPING EYE IN EIR SATELLITE 
IMAGERY.   

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: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 59 KTS AT 260000Z
   CIMSS AIDT: 51 KTS AT 260000Z
   CIMSS DPRINT: 50 KTS AT 260000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 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: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: INCREASED PEAK INTENSITY TO 90 KNOTS
BASED ON RECENT RAPID INTENSIFICATION OVER THE PHILIPPINES.

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 
90 KNOTS IS HIGHER THAN THE PREVIOUS WARNING AND WILL OCCUR NEAR
TAU 48 AFTER A PERIOD OF OPTIMAL ENVIRONMENTAL CONDITIONS. AFTER TAU 
84, THE SYSTEM WILL INTERACT WITH AN UPPER-LEVEL SUBTROPICAL TROUGH, 
WITH ABOUT 30-35 KNOTS OF VERTICAL WIND SHEAR (VWS). VWS IS EXPECTED 
TO INCREASE QUICKLY TO 45 KNOTS BY TAU 120 AS THE SYSTEM GAINS 
LATITUDE AND SST VALUES WILL DECREASE TO 22-24 C; 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 110 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 251800Z GEFS ENSEMBLE 
INDICATES A TIGHT CLUSTER OF SOLUTIONS ALONG THE JTWC FORECAST TRACK. 
THE 251800Z ECMWF ENSEMBLE (EPS) DOES SHOW A WIDER SPREAD OF 
SOLUTIONS, WITH SEVEN SOLUTIONS (ROUGHLY 15 PERCENT) 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.   

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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