WDPN31 PGTW 040900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (YINXING) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.1N 131.5E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 618 NM EAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 18 KTS SIGNIFICANT WAVE HEIGHT: 27 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 24W (YINXING) CONTINUES TO QUICKLY TRAVERSE TOWARDS THE NORTHWEST IN THE PHILIPPINE SEA, WHILE STEADILY INTENSIFYING. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC), WITH RAPIDLY DEVELOPING CONVECTIVE TOWERS MERGING INTO A COMPACT CENTRAL DENSE OVERCAST (CDO) FEATURE OVER THE LAST HOUR OR TWO. A 040426Z NOAA-20 ATMS 88.2GHZ IMAGE SHOWED A FAIRLY WELL-DEFINED LOW EMISSIVITY REGION (LER) TO THE NORTH OF A WEAK BAND OF CYCLONICALLY CURVED CONVECTION. A LATER 040644Z F18 SSMIS 91GHZ IMAGE SHOWED STRENGTHENING BANDING FEATURES AND A NASCENT MICROWAVE EYE FEATURE. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE MICROWAVE IMAGES NOTED ABOVE, THOUGH A MODEST AMOUNT OF SOUTHEASTERLY SHEAR IS STILL CREATING A SMALL AMOUNT OF VORTEX TILT AND THE LLCC IS LIKELY HANGING BACK TO THE SOUTHEAST FROM THE UPPER-LEVEL MICROWAVE EYE FEATURE. THE INITIAL INTENSITY IS SET WITH MEDIUM CONFIDENCE, BASED ON THE T3.5 DVORAK CURRENT INTENSITY ESTIMATES FROM KNES AND RCTP, THE 0638Z DMINT ESTIMATE OF 52 KNOTS AND THE 0600Z SATCON ESTIMATE OF 56 KNOTS. THE ANALYSIS MAY BE A TAD LOW, ESPECIALLY IN LIGHT OF THE RAPID CONVECTIVE DEVELOPMENT OVER THE LAST COUPLE OF HOURS. THE ENVIRONMENT IS FAVORABLE FOR FURTHER DEVELOPMENT, WITH LOW DEEP-LAYER SOUTHEASTERLY SHEAR, STRONG POLEWARD AND WESTWARD OUTFLOW, AND WARM SSTS. THE ONLY SOMEWHAT OFFSETTING FACTOR IS THE MODERATE MID-LEVEL SHEAR AS INDICATED BY THE LATEST CIMSS MID-LEVEL SHEAR ANALYSIS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.0 - 30 KTS RCTP: T3.5 - 55 KTS KNES: T3.5 - 55 KTS CIMSS SATCON: 56 KTS AT 040600Z CIMSS ADT: 53 KTS AT 040520Z CIMSS AIDT: 46 KTS AT 040600Z CIMSS DPRINT: 58 KTS AT 040600Z CIMSS DMINT: 52 KTS AT 040638Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 24W WILL CONTINUE TO TRACK TOWARDS THE NORTHWEST AT A STEADY 18 KNOTS FOR THE NEXT 12 TO 18 HOURS, ALONG THE SOUTHWESTERN SIDE OF THE STRONG STR TO THE NORTHEAST. THE SYSTEM BEGINS TO SLOW DOWN BY TAU 24 AS A RAPIDLY MOVING MID-LATITUDE TROF PASSES BY TO THE NORTH AND OPENS UP A BREAK IN THE STEERING RIDGE, WEAKENING THE OVERALL STEERING INFLUENCE OF THE STR. BY TAU 36, TRACKS SPEEDS DROP OFF DRAMATICALLY AS THE SYSTEM RUNS HEADLONG INTO THE LEADING EDGE OF A STRONG COLD-SURGE PUSHING SOUTH OUT OF THE EAST CHINA SEA TO THE EAST OF TAIWAN. BETWEEN TAU 48 AND TAU 72, THE SYSTEM WILL SLOW TO ABOUT 4-5 KNOTS AS TRANSITS A WEAK DEEP-LAYER STEERING PATTERN AND CONTINUES TO BUTT UP AGAINST THE NORTHEASTERLY SURGE FLOW. OVER THAT TIME, THE SYSTEM WILL START TO FEEL THE INFLUENCE OF THE EAST-NORTHEASTERLY FLOW AND TURN ONTO A MORE WESTWARD TRACK BY TAU 72. AFTER TAU 72, A STR SOUTH OF HONG KONG QUICKLY BUILDS AND EXTENDS OVER TAIWAN TO THE NORTH OF TS 24, RESULTING IN AN INCREASE IN TRACK SPEEDS AS THE SYSTEM MOVES WEST INTO THE NORTHERN PORTION OF THE SOUTH CHINA SEA. IN TERMS OF INTENSITY, THE SYSTEM IS FORECAST TO RAPIDLY INTENSIFY OVER THE NEXT 24 HOURS UNDER LOW SHEAR CONDITIONS WITH STRONG POLEWARD OUTFLOW. THE SYSTEM WILL PEAK AROUND TAU 36, BEFORE UPPER-LEVEL OUTFLOW CONDITIONS WEAKEN A BIT. MORE IMPORTANTLY HOWEVER, WILL BE THE INFLUENCE OF THE OCEAN CONDITIONS AFTER TAU 24. BETWEEN ROUGHLY TAU 24 TO TAU 60, THE SYSTEM WILL TRACK DIRECTLY OVER THE TRACK OF STY 23W WHEN IT WAS AT ITS MAXIMUM INTENSITY, AND THE COLD WAKE LEFT BEHIND. AT THE SAME TIME THAT IT IS DOING THIS, TRACK SPEEDS REACH THEIR MINIMUM, MAXIMIZING THE OCEAN COOLING EFFECT ON TS 24W. THUS, AT BEST THE SYSTEM WILL STABILIZE AROUND 85-90 KNOTS, BUT COULD ACTUALLY SEE SOME MORE SIGNIFICANT WEAKENING AS IT SLOWS AND TURNS WESTWARD. ADDITIONALLY, AT THIS TIME IT WILL BE HAVING TO FEND OFF DRY AND RELATIVELY COOL AIR ASSOCIATED WITH THE COLD SURGE, WHICH WILL BE TRYING TO PUSH INTO THE CORE OF THE SYSTEM. THE MORE IMPACT THE OCEAN CONDITIONS HAVE ON THE INTENSITY, THE MORE THE DRY AIR WILL BE ABLE TO PENETRATE THE SYSTEM CORE. OVERALL, TS 24W WILL WEAKEN AS IT MOVES THROUGH THE LUZON STRAIT, BUT ONCE THERE, CONDITIONS WILL IMPROVE, ALLOWING FOR A STEADY INTENSITY OR POSSIBLY REINTENSIFICATION AFTER TAU 96. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT OVER THE PAST COUPLE OF MODEL RUNS. AT TAU 72, CROSS-TRACK SPREAD AMONGST THE CONSENSUS MEMBERS IS JUST 90NM, WITH THE JGSM ON THE LEFT OF TRACK AND THE NAVGEM ON THE RIGHT. MODEL SPREAD INCREASES SHARPLY AFTER TAU 72 HOWEVER, BOTH IN THE CROSS- AND ALONG-TRACK AXES. CROSS-TRACK SPREAD INCREASES TO 180NM BY TAU 120 BETWEEN THE GALWEM ON THE SOUTH SIDE AND NAVGEM ON THE NORTH SIDE, STARTING TO PULL THE SYSTEM POLEWARD TOWARDS TAIWAN. ALONG-TRACK SPREAD ALSO INCREASES, PARTICULARLY BETWEEN THE GFS WHICH IS THE FASTEST MODEL, TRACKING THE CENTER WELL INTO THE SOUTH CHINA SEA, AND THE ECMWF WHICH KEEPS THE SYSTEM JUST OFF THE NORTHWEST TIP OF LUZON. ENSEMBLE SPREAD HAS ALSO IMPROVED SINCE YESTERDAY, WITH ONLY A COUPLE OF GEFS AND ECENS MEMBERS SHOWING A RECURVE TO THE NORTHEAST. THE JTWC FORECAST LIES VERY CLOSE TO THE GEFS ENSEMBLE MEAN THROUGH THE FORECAST WITH INCREASING CONFIDENCE DUE TO THE IMPROVED ENSEMBLE AND DETERMINISTIC AGREEMENT. INTENSITY GUIDANCE IS MIXED, WITH THE CTCX AND GFS PEAKING THE SYSTEM AROUND 70 KNOTS, WHILE THE REMAINDER OF THE GUIDANCE INCLUDING HAFS-A, HWRF AND MULTIPLE RAPID INTENSIFICATION (RI) AIDS INCLUDING RICN, DTOPS, AND CTR1 ARE SUPPORTING A PEAK BETWEEN 90-115 KNOTS. THE MULTI-MODEL CONSENSUS (INCLUDING RI AIDS) MEAN PEAKS AT TAU 48 AT 93 KNOTS AND THE JTWC FORECAST CLOSELY FOLLOWS THIS MEAN (ICNE) THROUGH THE FORECAST PERIOD, WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN