WDPN33 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (CO-MAY) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 120.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 350 NM SOUTH OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
FULLY-OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH
TROPICAL STORM (TS) 11W (CO-MAY), WHICH IS NOW POSITIONED JUST
NORTH OF LUZON. THIS MARKS A MINOR CHANGE FROM A PRIOR ASSESSMENT,
WHICH DETERMINED LANDFALL IN VICINITY OF LUNA, PHILIPPINES. SURFACE
WIND OBSERVATIONS FROM VIGAN WMO STATION CLOSER TO 250030Z AND
250100Z INDICATED WESTERLY DIRECTION, WITH A MORE RELIABLE, 10 KTS
WIND SPEEDS. SYNTHESIS OF NOW AVAILABLE DATA LED TO A 50-55 NM
ADJUSTMENT OF THE 250000Z BEST TRACK POSITION TO THE NORTHWEST. THE
INITIAL POSITION FOR CURRENT FORECAST IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE ANIMATED VISIBLE AND INFRARED SATELLITE
IMAGERY DEPICTING CONVECTIVE BANDS WRAPPING INTO A NEARLY FULLY 
OBSCURED LLCC, SUPPORTED BY A 250537Z NOAA-20 ATMS MICROWAVE IMAGE. 
THE INITIAL INTENSITY OF 45 KTS IS ALSO ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE EXTRAPOLATION FROM A 250151Z METOP-C ASCAT 
PASS, AS WELL AS AGENCY DVORAK FIXES AND OBJECTIVE ESTIMATES LISTED 
BELOW. HOWEVER, RECENT IMPACTS FROM PROXIMITY TO LAND INCREASE 
UNCERTAINTY ASSOCIATED WITH CURRENTLY AVAILABLE DATA.

INITIAL WIND RADII BASIS: 250151Z METOP-C ASCAT PASS

CURRENT STEERING MECHANISM: NEAR EQUATORIAL RIDGE (NER) TO THE
SOUTHEAST, AS WELL AS LARGE CYCLONIC CIRCULATION CENTERED OVER
TAIWAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS SATCON: 50 KTS AT 250515Z
   CIMSS ADT: 47 KTS AT 250540Z
   CIMSS AIDT: 55 KTS AT 250730Z
   CIMSS D-MINT: 46 KTS AT 250515Z
   CIMSS D-PRINT: 36 KTS AT 250730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: TERRAIN INTERACTION

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: BEST TRACK POSITION FOR 250000Z HAS
BEEN ADJUSTED BASED ON NEW SURFACE WIND OBSERVATION AND SATELLITE 
IMAGERY DEPICTING THE LOW-LEVEL CIRCULATION CENTER TRANSITING CLOSER 
TO 
THE WESTERN COASTLINE OF LUZON

FORECAST DISCUSSION: TS 11W IS FORECAST TO ACCELERATE AND TRANSIT
ALONG THE NORTHWESTERN PERIPHERY OF A NER CENTERED TO THE SOUTHEAST
AND UNDER THE INFLUENCE FROM THE SOUTHEASTERN PERIPHERY OF THE
AFOREMENTIONED LARGE-SCALE CYCLONIC CIRCULATION. DESPITE FAVORABLY
WARM (29-30 C) SEA SURFACE TEMPERATURES (SST), THE SYSTEM IS
EXPECTED TO IMMEDIATELY BEGIN WEAKENING, DUE TO INCREASING VERTICAL
WIND SHEAR (VWS), WEAKENING UPPER LEVEL OUTFLOW AND INCREASING DRY
AIR ENTERING THE CORE OF THE VORTEX. WHILE THE SYSTEM TRACKS
NORTHEAST FOR THE NEXT 24 HOURS, IT WILL BEGIN TO INTERACT WITH
TROPICAL DEPRESSION 10W, WHICH IS LOCATED JUST NORTH OF TAIWAN, AND
IS EXPECTED TO BE PULLED TOWARD IT. THE EXTENT OF THE INTERACTION IS 
LIKELY GOING TO BE MINOR, DUE TO RELATIVELY LOW INTENSITIES OF BOTH 
SYSTEMS. AT THE SAME TIME, THE LARGE CYCLONIC CIRCULATION CENTERED 
OVER TAIWAN, WILL REORIENT FROM A SOUTHWEST-NORTHEAST AXIS, INTO A 
ZONAL POSITIONING RESEMBLING A REVERSE ORIENTED MONSOONAL TROUGH, 
RESULTING IN TS 11W TURNING EASTWARD. SIMULTANEOUSLY, TS CO-MAY IS 
FORECAST TO BEGIN DISSIPATING AROUND TAU 24-36, LEADING TO 
ENCAPSULATION OF WHAT IS LEFT OF THE VORTEX INTO THE PREDOMINANT 
WESTERLY FLOW.

MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN FAIR
AGREEMENT THROUGH THE INITIAL 24-36 HOURS AS INDICATED BY A 75-125
NM CROSS-TRACK SPREAD. ALL MODELS INDICATE A NORTHEASTWARD TRACK
FOLLOWED BY A DRASTIC SLOWDOWN. AFTER THAT, MAJORITY OF THE
GUIDANCE DISSIPATES THE VORTEX, WHICH RESULTS IN ERRATIC TRACK
GUIDANCE AFTERWARD. JTWC OFFICIAL FORECAST IS LAID WITH MEDIUM 
CONFIDENCE AND CLOSE TO THE MULTI-MODEL CONSENSUS, LEANING CLOSER TO 
THE DETERMINISTIC GFS TRACK AFTER TAU 24, WHICH IS LIKELY CORRECTLY 
REPRESENTING THE STEERING ENVIRONMENT. JTWC INTENSITY GUIDANCE IS ALSO 
ASSESSED WITH MEDIUM CONFIDENCE, BASED ON ALL DETERMINISTIC
GUIDANCE AGREEING ON A WEAKENING TREND THROUGHOUT THE FORECAST
PERIOD. AFTER TAU 36, UNCERTAINTY INCREASES, WITH SOME MODELS
INDICATING POTENTIAL FOR INTENSIFICATION, WHICH MAY BE ATTRIBUTED
TO A VORTEX CALCULATION JUMP ONTO A DIFFERENT CIRCULATION DEVELOPING 
IN PROXIMITY OF OKINAWA.

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