Western Pacific: 19W(CHANTHU) CAT 2 weakening gradually,18W(CONSON): final warning// Invest 95B: intensity near 35knots, 12/21utc updates

TD 18W(CONSON). WARNING 28/FINAL ISSUED AT 12/21UTC.REMARKS: 122100Z POSITION NEAR 15.6N 108.8E. 12SEP21. TROPICAL DEPRESSION (TD) 18W (CONSON), LOCATED APPROXIMATELY 110 KM SOUTHEAST OF DA NANG, VIETNAM, HAS TRACKED NORTHWESTWARD AT 02 KM/H OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY AND ANIMATED RADAR IMAGERY DEPICT A DECAYING LOW- LEVEL CIRCULATION WITH A WEAKLY DEFINED CENTER. UPPER-LEVEL ANALYSIS INDICATES UNFAVORABLE CONDITIONS WITH MODERATE TO STRONG EASTERLY VERTICAL WIND SHEAR, WHICH WILL PERSIST THROUGH THE FORECAST PERIOD. SURFACE OBSERVATIONS FROM QUANG NGAI, 40KM TO THE SOUTHWEST, INDICATE STEADILY RISING SLP WITH A 12/18Z SLP VALUE AT 1001.4MB REFLECTING THE STEADY WEAKENING TREND. THE SYSTEM IS FORECAST TO TRACK NORTHWESTWARD INTO VIETNAM WITH DISSIPATION BY 12H. THIS IS THE FINAL WARNING ON THIS SYSTEM BY THE JOINT TYPHOON WRNCEN PEARL HARBOR HI. THE SYSTEM WILL BE CLOSELY MONITORED FOR SIGNS OF REGENERATION. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 121800Z IS 12 FEET.

TY 19W(CHANTHU). WARNING 27 ISSUED AT 12/21UTC.SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TY 19W CONTINUES TO TRACK GENERALLY NORTHWARD ALONG THE WESTERN PERIPHERY OF A NORTH-SOUTH ORIENTED SUBTROPICAL RIDGE(STR) TO THE EAST. THE PAST SIX HOURS HAS SEEN THE TRACK TREND A BIT FURTHER EAST OF NORTH THAN EXPECTED, BUT THIS IS LIKELY JUST A WOBBLE AND THE OVERALL TRACK IS FORECAST TO BE NORTH THROUGH THE NEXT 12 TO 24 HOURS. BETWEEN 24H AND 36H, A DEEP STR IS EXPECTED TO BUILD TO THE NORTHWEST OF THE SYSTEM WITH RIDGING EXTENDING EASTWARD ACROSS THE KOREAN PENINSULA, COCOONING TY 19W IN A COMPETING STEERING ENVIRONMENT. IN RESPONSE, TY 19W WILL SLOW AND BECOME QUASI-STATIONARY AND STALL IN THE VICINITY OF SHANGHAI BETWEEN 36h AND 72H. BY 72H A FAIRLY STRONG MID-LATITUDE MAJOR SHORTWAVE TROUGH WILL BEGIN TO ERODE THE STR TO THE WEST, WHILE THE STR TO THE EAST MOVES SOUTHWEST AND BUILDS. THE COMBINATION OF THE REORIENTATION OF STR TO THE EAST AND THE APPROACHING TROUGH FROM THE WEST WILL KICK TY 19W ONTO AN ACCELERATING EASTWARD TRACK. AS THE SYSTEM SKIRTS THE SOUTHERN KOREA COASTLINE, IT WILL BECOME EMBEDDED UNDER STRONG WESTERLY FLOW ALOFT AND BEGIN EXTRATROPICAL TRANSITION (ETT). THE UPPER-LEVEL OUTFLOW PATTERN HAS SHIFTED OVER THE PAST 12 HOURS, WITH A 200MB ANTI-CYCLONE NOW FIRMLY IN PLACE JUST EAST OF THE SYSTEM. WHILE THIS POSITIONING SUPPORTS A STRONG POLEWARD OUTFLOW CHANNEL, THE PREVIOUSLY STRONG EQUATORWARD CHANNEL HAS WEAKENED. THIS PATTERN IS EXPECTED TO CONTINUE AND THE REDUCTION TO ONE OUTFLOW CHANNEL WILL BE THE PRIMARY MECHANISM TO WEAKEN THE SYSTEM OVER THE NEXT 24 TO 36 HOURS. BY 48H A 200MB RIDGE WILL MOVE DIRECTLY OVER THE SYSTEM, EFFECTIVELY CHOKING OFF ANY SIGNIFICANT OUTFLOW MECHANISM AND LEADING TO MORE RAPID WEAKENING THROUGH 72H. ONCE THE SYSTEM STARTS MOVING EAST IT WILL TAP INTO ROBUST DIVERGENT OUTFLOW AHEAD OF THE APPROACHING TROUGH, BUT RAPIDLY INCREASING VERTICAL WIND SHEAR WILL OFFSET THIS OUTFLOW RESULTING IN A STEADY INTENSITY THROUGH THE REMAINDER OF THE FORECAST.

TY 19W(CHANTHU).SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THAT TY 19W HAS UNDERGONE SIGNIFICANT WEAKENING OVER THE PAST SIX HOURS, WITH CONVECTIVE CLOUD TOPS WARMING SIGNIFICANTLY AND THE EYE COOLING AND FILLING. HIGH RESOLUTION MODELING INDICATES DRY, DESCENDING AIR IS BEING ENTRAINED INTO THE SOUTHWESTERN SIDE OF THE SYSTEM. ADDITIONALLY, CIMSS SHEAR ANALYSIS REVEALS MODERATE SOUTHWESTERLY SHEAR IS NOW IMPINGING ON THE SYSTEM. FINALLY, OVER THE PAST SIX HOURS THE SYSTEM HAS MOVED OVER AN EDDY OF LOW OCEAN HEAT CONTENT. THE COMBINATION OF ALL THESE FACTORS HAS LED TO THE RAPID WEAKENING. ANIMATED RADAR IMAGERY DEPICTS THE DEVELOPMENT OF A MOAT OF WEAK RADAR RETURNS SURROUNDING A COMPACT CORE OF CONVECTION WHICH IS WRAPPING INTO THE ILL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON RJTD RADAR FIXES AND THE 19-KM RAGGED EYE IN THE EIR. THE INITIAL INTENSITY IS ASSESSED AT 95 KNOTS/CAT 2 WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE AGENCY CURRENT INTENSITY ESTIMATES BETWEEN 5.0-5.5. AGENCY DATA-T NUMBERS ARE MUCH LOWER, IN THE T4.5 (77 KTS) RANGE, WHILE THE ADT AND SATCON APPEAR UNREASONABLY HIGH BASED ON THE RAPIDLY DETERIORATING STRUCTURE. A 121106Z ASCAT-B PASS PROVIDED SOLID DATA TO DRAMATICALLY REDUCE THE SIZE OF THE WIND FIELD. ANALYSIS REVEALS AN INCREASINGLY MARGINAL ENVIRONMENT WITH INCREASING SOUTHWESTERLY SHEAR, DECREASING SSTS AND STEADILY DECREASING OUTFLOW ALOFT.

TY 19W(CHANTHU).MICROWAVE DATA SHOW THE DEVELOPMENT OF A MOAT OF WEAK RADAR RETURNS SURROUNDING A COMPACT CORE OF CONVECTION WHICH IS WRAPPING INTO THE ILL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC).

TY 19W(CHANTHU).MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN GOOD AGREEMENT WITH MINIMAL CROSS- AND ALONG-TRACK SPREAD THROUGH 24H. BETWEEN 36H AND 72H HOWEVER, THE MODELS DEPICT WHAT IS KNOWN AS A SQUASHED SPIDER PATTERN WITH TRACKERS RANDOMLY SCATTERED WITHIN A 280KM CIRCLE CENTERED OVER SHANGHAI. THIS IS NOT UNEXPECTED DUE TO THE WEAK AND COMPETING STEERING INFLUENCES, THOUGH IT LENDS VERY HIGH UNCERTAINTY TO THE TRACK FORECAST THROUGH 72H. THE JTWC FORECAST LIES ON THE EASTERN SIDE OF THE GUIDANCE CLUSTER THROUGH 72H. TRACK GUIDANCE FIRMS UP AFTER 72H, WITH THE BULK OF THE TRACKERS TIGHTLY CLUSTERED ON A TRACK OVER THE SOUTHERN COAST OF KOREA THROUGH 120H. THE EGRR AND GALWEM ARE THE NOTABLE OUTLIERS, TRACKING THE SYSTEM OVER CENTRAL KYUSHU. THE EXTENDED FORECAST LIES TO THE NORTH OF THE CONSENSUS MEAN WITH LOW CONFIDENCE DUE TO THE UNCERTAINTIES AROUND THE TIMING OF THE TURN TO THE EAST. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON THE STEADY WEAKENING TREND, THOUGH THE JTWC FORECAST LIES ABOUT FIVE KNOTS HIGHER THAN THE CONSENSUS MEAN, WITH MEDIUM CONFIDENCE.

TY 19W(CHANTHU). HWRF AT 12/12UTC. INTENSITY GUIDANCE: 92KNOTS AT +0H.

INVEST 95B. TROPICAL CYCLONE FORMATION ALERT ISSUED AT 12/07UTC. UPDATE AT 12/18UTC.THE AREA OF CONVECTION (INVEST 95B) PREVIOUSLY LOCATED NEAR 16.0N 88.0E IS NOW LOCATED NEAR 20.0N 81.6E, APPROXIMATELY 285 KM SOUTH-SOUTHWEST OF KOLKATA, INDIA. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A CONSOLIDATING LOW LEVEL CIRCULATION CENTER (LLCC) WITH IMPROVED CONVECTIVE BANDING. A 121427Z METOP-A PASS REVEALS A SWATH OF 30-35 KT WIND BARBS OVER THE SOUTHWEST QUADRANT OF THE SYSTEM WITH WEAKER (10-15 KT) WINDS OVER THE NORTHERN SEMICIRCLE. ANIMATED RADAR IMAGERY FROM THE PARADIP RADAR INDICATES BETTER ORGANIZATION WITH DEEP CONVECTIVE BANDING OVER THE SOUTHERN SEMICIRCLE WRAPPING INTO THE SOUTHEAST QUADRANT. ENVIRONMENTAL ANALYSIS NOW INDICATES A LESS FAVORABLE ENVIRONMENT DUE TO MODERATE TO HIGH (20-30 KT) VERTICAL WIND SHEAR (VWS) OFFSET BY GOOD EQUATORWARD OUTFLOW ALOFT AND VERY WARM (29-30C) SEA SURFACE TEMPERATURES (SST).MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 30 TO 35 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 993 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS HIGH.

INVEST 95B. GLOBAL MODELS ARE GOOD IN AGREEMENT THAT INVEST 95B WILL CONTINUE TO CONSOLIDATE AND TRACK NORTHWESTWARD OVER THE NEXT 12 TO 24 HOURS AND THERE EXISTS A BRIEF WINDOW OF OPPORTUNITY FOR THE SYSTEM TO REACH MINIMAL TROPICAL STORM STRENGTH PRIOR TO LANDFALL ALONG THE NORTHEAST COAST OF INDIA.

INVEST 95B. HWRF AT 12/12UTC. INTENSITY GUIDANCE: 37KNOTS AT +6H.

12/2030UTC.