WDPN32 PGTW 041500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) WARNING NR 025// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 23W (ATSANI), LOCATED APPROXIMATELY 382 NM SOUTH OF KADENA AB, HAS TRACKED WEST-SOUTHWESTWARD AT 03 KNOTS OVER THE OF KADENA AB, HAS TRACKED WEST-SOUTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) SHOW AN INTENSIFYING SYSTEM, WITH DEEP CONVECTION STARTING TO BLOOM I AN INTENSIFYING SYSTEM, WITH DEEP CONVECTION STARTING TO BLOOM INTO A SYMMETRIC COLD DENSE OVERCAST (CDO) OVER THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A VERY TIMELY 041202Z ASCAT-A BULLSEYE PASS, WHICH CONFIRMS THE LLCC HAS TUCKED UNDER THE DEVELOPING CDO. WHICH CONFIRMS THE LLCC HAS TUCKED UNDER THE DEVELOPING CDO. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON A SLIGHT HEDGE BELOW THE PGTW CURRENT INTENSITY ESTIMATE OF T3.5(55 KNOTS), MORE IN LINE WITH THE REMAINDER OF SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES GROUPED AROUND THE 50 KNOT MARK, CONFIRMED BY THE PREVIOUSLY MENTIONED ASCAT PASS WHICH SHOWED 45-50 KNOT PREVIOUSLY MENTIONED ASCAT PASS WHICH SHOWED 45-50 KNOT WIND BARBS ON THE NORTHWEST SIDE OF THE CIRCULATION. BASED ON THE SATELLITE APPEARANCE OVER THE PAST SIX HOURS, THE ENVIRONMENT HAS CLEARLY IMPROVED, WITH DECREASING VWS AS EVIDENCED BY THE DEVELOPMENT OF TRANSVERSE BANDING ON THE EASTERN (UPSHEAR) SIDE OF THE SYSTEM. OUTFLOW HAS ALSO IMPROVED AND IS NOW TAPPING INTO A POLEWARD CHANNE IMPROVED AND IS NOW TAPPING INTO A POLEWARD CHANNEL, ALLOWING FOR THE BURST IN CONVECTION. THE SYSTEM REMAINS OVER WARM WATER IN CONVECTION. THE SYSTEM REMAINS OVER WARM WATERS (28-29 DEG CELSIUS) CONDUCIVE FOR STRENGTHENING. THE ASCAT PASS CONFIRMS THAT THE SYSTEM HAS STARTED MOVING TOWARDS THE WEST, AS THE STEERING STR BEGINS TO BUILD AND EXTEND TOWARDS THE WEST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 23W HAS BEGUN ITS WESTWARD MOVEMENT AS THE STR TO THE NORTHEAST BUILDS IN TO THE NORTH, AND IT IS FORECAST THAT TS 23W WILL ACCELERATE ALONG THIS GENERAL WEST- WILL ACCELERATE ALONG THIS GENERAL WEST-NORTHWEST MOTION TAU 36. AFTER TAU 36, THE SYSTEM WILL SLOW SOMEWHAT A TAU 36, THE SYSTEM WILL SLOW SOMEWHAT AS STR WEAKENS SLIGHT AND REORIENTS TO A MORE SOUTHWEST-NORTHEAS REORIENTS TO A MORE SOUTHWEST-NORTHEAST ORIENTATION. NEAR THE TAU 60 POINT, THE PRIMARY STEERING MECHANISM WILL S THE PRIMARY STEERING MECHANISM WILL SHIFT TO THE STR LOCATED OVER CENTRAL CHINA, WHICH WILL SERVE TO S CENTRAL CHINA, WHICH WILL SERVE TO SHIFT THE TRACK MORE SOUTHWESTWARD BY TAU 72. WHILE THE SYSTEM HAS RECENTLY TAPPED INTO A STRONG POLEWARD OUTFLOW CHANNEL, 200MB MODEL FIELDS AND ANALYSIS INDICATES THAT THIS CHANNEL WILL BE SHORT-LIVED, REPLACED BY A SINGLE WESTWARD OUTFLOW PATTERN, WHICH WHEN COMBINED WITH LOW VWS AND WARM SSTS WILL SUPPORT STEADY INTENSIFICATION TO A PEAK OF 70 KNOTS AT TAU 36. ANOTHER SHORT- TERM BURST OF POLEWARD O SHORT- TERM BURST OF POLEWARD OUTFLOW IS LIKELY BETWEEN TAU 36 AND 48 WHICH WILL SERVE TO OFFSET DECREASED SSTS AND INCREASING VWS TO ALLOW FOR A PERIOD OF STEADY INTENSITY A PERIOD OF STEADY INTENSITY THROUGH TAU 72. MODEL GUIDANCE HAS BEEN TRENDING MORE NORTHWESTWARD, ESPECIALLY BETWEEN TAUS 36 AND 60 BUT SPREAD IS VERY LOW (100 NM) THROUGH TAU 72. THE NVGM REMAINS THE SOLE OUTLIER, STILL TAKIN SOLE OUTLIER, STILL TAKING THE SYSTEM WELL TO THE NORTH OVER TAIWAN. THE JTWC FORECAST LIES ALONG THE NORTHERN EDGE OF GUIDANCE ENVELOPE THROUGH TAU 72 FAIR CONFIDENCE. THE INTENSITY FORECAST IS HEDGED SLIGHTLY ABOVE THE MULTI-MODEL INTENSITY CONSENSUS WITH FAIR CONFIDENCE IN RESPECT TO A VERY AGGRESSIVE HWRF SOLUTION WHICH INDICATES A PEAK INTENSITY OVER 90 KNOTS BY TAU 48. C. IN THE EXTENDED TAUS, THE SYSTEM WILL ENTER THE NORTHERN PORTION OF THE SOU PORTION OF THE SOUTH CHINA SEA BY TAU 72 ON A GENERALLY WEST-SOUTHWESTWARD TRACK ALONG THE SOUTHEAST PERIPHERY OF THE STR OVER CENTRAL CHINA. SIMULTANEOUSLY, THE COMBINATION OF INCREASED VWS, CONVERGENT UPPER- LEVEL FLOW, ENTRAINMENT OF DRIER AIR FROM THE NORTH, AND COOLER SSTS WILL COMBINE TO STEADILY WEAKEN THE SYSTEM THROUGH TAU 120. AS THE SYSTEM WEAKENS, IT WILL COME UNDER THE STEERING INFLUENCE OF THE LOW TO MID-LEVEL FLOW FROM THE NORTHEAST, LEADING TO A SOUTHWESTWARD TRACK THROU TRACK THROUGH TAU 120. TS 23W IS FORECAST TO MAKE LANDFALL ALONG THE SOUTHERN VIETNAMESE COASTLINE JUST PRIOR TO TAU 120 BEFORE TRACKING INLAND TOWARDS THE SOUTHWEST. DISCOUNTING THE NAVGEM AND ECMWF WHICH TRACK THE SYSTEM INTO THE TAIWAN STRAITS AND LOSS THE VORTEX BY TAU 72, THE REMAINDER OF THE CONSENSUS MEMBERS ARE IN GOOD CROSS-TRACK AGREEMENT THROUGH TAU 120 WITH A 165NM SPREAD AT TAU 120. HOWEVER, ALONG-TRACK SPREAD INCREASES DRAMATICALLY AFTER TAU 72, INCREASING TO A TO ABOUT 200NM BY TAU 120. THE JTWC FORECAST TRACK LIES VERY CLOSE TO THE THE MULTI-MODEL CONSENSUS THROUGH TAU 120 WITH LOW CONFIDENCE DUE TO THE UNCERTAINTY IN THE TIMING OF THE TURN TO THE SOUTHWEST AND THE ALONG- TRACK SPREAD.// NNNN