WDPN33 PGTW 152100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NESAT) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2N 122.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 286 NM NORTH-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION WRAPPING INTO A PERSISTENT DEEP CONVECTIVE CLOUD
STRUCTURE, WHICH IS OBSCURING THE LOW-LEVEL CIRCULATION CENTER
(LLCC). EIR INDICATES CONVECTIVE BURSTS, FLARING WITHIN THE
CONVECTIVE MASS WITH CLOUD TOPS TEMPERATURES OF (-87C). THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON AGENCY DVORAK
POSITION FIXES, IN COMBINATION WITH AN EARLIER 151327Z ASCAT-B
IMAGE, WHICH SHOWS A DEFINED LLCC WITH 40-45 KNOT WINDS OVER THE
SOUTHEASTERN PERIPHERY. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED
WITH HIGH CONFIDENCE BASED ON THE PGTW, KNES DVORAK INTENSITIY
ESTIMATES OF T3.0, ASCAT DATA, ALSO SUPPORTED BY THE ADT AND AIDT
AS WELL AS THE EXPERIMENTAL CIMSS DEEP MICRONET (DMN) AND
OPEN-AIIR, BOTH ESTIMATING AN INTENSITY OF 45 KNOTS AT 1800Z.
ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH MODERATE WESTWARD
OUTFLOW, WARM (29-30C) SEA SURFACE TEMPERATURES (SSTS), AND
MODERATE (10-15KTS) VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED SOUTHEAST OF KYUSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 43 KTS AT 151430Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 23W (NESAT) WILL TRACK NORTHWESTWARD ALONG
THE SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED SOUTHEAST OF KYUSHU OVER THE NEXT 12 HOURS. ADDITIONALLY,
A MID-LATITUDE TROUGH WILL MOVE IN FROM THE WEST WHICH WILL ERODE
THE STR AND INDUCE A WEAKNESS WHICH WILL PULL TS 23W SLIGHTLY MORE
POLEWARD THROUGH TAU 36. AFTER TAU 36, AS THE TROUGH TRANSITS
EASTWARD, THE SYSTEM WILL THEN BEGIN TO SLOW AND MOVE SOUTHWESTWARD
AS A STR CENTERED OVER NORTHERN MYANMAR WILL BUILD TOWARDS THE EAST
AND ASSUME THE DOMINANT STEERING ROLE. AS THIS OCCURS, AN
ASSOCIATED SURFACE HIGH PRESSURE SYSTEM WILL INDUCE STRONG
NORTHEASTERLY FLOW WHICH WILL CONTINUE TO STEER THE SYSTEM
SOUTHWESTWARD THROUGH TAU 72. BY TAU 96, THE STR SHIFTS AND BUILDS
OVER THE TAIWAN STRAIT, ALLOWING FOR TS 23W TO TURN NORTHWESTWARD
ONCE MORE TOWARDS THE END OF THE FORECAST, SKIRTING THE COAST OF
HAINAN. TS 23W WILL STEADILY INTENSIFY THROUGH TAU 48, AS POLEWARD
OUTFLOW IMPROVES BY ENHANCED UPPER LEVEL WESTERLIES WHILE THE
SYSTEM TRACKS OVER WARM (29-30C) SSTS AND HIGH OCEAN HEAT CONTENT.
BETWEEN TAU 96 AND TAU 120, THE NORTHEASTERLY SURGE EVENT WILL 
INCREASE VERTICAL WIND SHEAR (VWS) WHILE INCREASING DRY AIR AROUND 
THE SYSTEM WHICH WILL RESULT IN STEADY WEAKENING THROUGH THE END OF 
THE FORECAST.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 72, WITH A LARGE SPREAD OF 150-250NM FROM TAU 96 TO TAU
120. THE BULK OF THE ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS)
SOLUTIONS SUPPORT THE JTWC FORECAST TRACK THROUGH TAU 72, WITH
INCREASING UNCERTAINLY BETWEEN TAU 96 AND TAU 120. THEREFORE, THE
JTWC FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL
CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72 AND ASSESSED WITH
MEDIUM CONFIDENCE THROUGH THE END OF THE FORECAST. THE INTENSITY
GUIDANCE REMAINS MIXED, WITH CTR1 AND HWRF REPRESENTS 
THE HIGH END OF GUIDANCE, PEAKING BETWEEN 90-105 KNOTS, WHILE THE
COTC AND DECAY SHIPS (NAVGEM AND GFS) REPRESENTS THE LOW END OF
GUIDANCE, PEAKING THE SYSTEM AT 60-70 KNOTS. ENSEMBLE INTENSITY
GUIDANCE CONTINUES TO SHOW VERY HIGH PROBABILITIES OF MODERATE
INTENSIFICATION. THE JTWC FORECAST IS PLACED WITH MEDIUM CONFIDENCE
AND LIES CLOSE TO THE HWRF SOLUTION AND ABOVE THE CONSENSUS MEAN. 


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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