Western Pacific: TS 18W(CONSON), TY 19W(CHANTHU) and Invest 96W: congested cyclonic traffic, 09/15 updates

TS 18W(CONSON). WARNING 15 ISSUED AT 09/15UTC.SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 18W IS CURRENTLY TRACKING WESTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE TO THE NORTHEAST. AROUND 48H, IT WILL TURN MORE WEST-NORTHWESTWARD AS A MID-LATITUDE TROUGH BEGINS TO DEEPEN TO THE NORTH, CREATING A WEAK STEERING ENVIRONMENT. THE SYSTEM IS EXPECTED TO MAKE LANDFALL OVER NORTHERN VIETNAM ROUGHLY 185 KM SOUTH OF HANOI. THE MARGINALLY FAVORABLE ENVIRONMENT WILL ALLOW SLIGHT INTENSIFICATION TO A PEAK OF 70 KNOTS/CAT 1 AROUND 48H. AFTERWARD, INCREASING VERTICAL WIND SHEAR AND LAND INTERACTION WITH THE COAST OF VIETNAM WILL WEAKEN THE SYSTEM TO 30 KNOTS JUST BEFORE LANDFALL AT ABOUT 96H.

TS 18W(CONSON). SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A DISORGANIZED SYSTEM THAT HAS IMPROVED SLIGHTLY IN STRUCTURE OVER THE PAST SIX HOURS. THE INITIAL POSITION IS BASED ON UPPER-LEVEL BANDING IN A 091055Z 91GHZ SSMIS IMAGE. THE INITIAL INTENSITY OF 45 KNOTS IS BASED ON THE MULTI-AGENCY DVORAK INTENSITY ESTIMATES. THE SYSTEM IS CURRENTLY TRACKING WESTWARD IN A MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE VERTICAL WIND SHEAR, WARM SEA SURFACE TEMPERATURES, AND WEAK RADIAL OUTFLOW ALOFT.

TS 18W(CONSON).MODEL DISCUSSION: NUMERICAL MODELS ARE IN BETTER AGREEMENT THAN THEY WERE PREVIOUS RUNS. ALL MODELS ARE NOW SHOWING A GENERALLY WESTWARD OR WEST-NORTHWESTWARD TRACK TOWARDS THE COAST OF VIETNAM. HOWEVER, THERE IS STILL A LOT OF UNCERTAINTY ABOUT WHERE THE SYSTEM WILL MAKE LANDFALL, AS CURRENT MODELS SHOW ABOUT A 550 KM SPREAD ACROSS VIETNAM. INTENSITY GUIDANCE IS IN FAIR AGREEMENT, WITH ALL MODELS SHOWING AN INTENSIFICATION PHASE WHICH PEAKS NEAR 70 KNOTS/CAT 1 AROUND 48H, FOLLOWED BY A STEADY WEAKENING TREND BEFORE LANDFALL.

TY 19W(CHANTHU). WARNING 14 ISSUED AT 09/15UTC. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TYPHOON (TY) 19W IS BEGINNING A MORE NORTHWESTWARD TRACK AS IT BEGINS TO ROUND THE WESTERN EDGE OF THE SUBTROPICAL RIDGE. AFTER 48H, THE SYSTEM WILL CROSS TAIWAN AS IT TRACKS NORTHWARD AND EVENTUALLY CRESTS THE SUBTROPICAL RIDGE AXIS. AFTER 96H, THE SYSTEM WILL TURN NORTH-NORTHEASTWARD ON THE POLEWARD SIDE OF THE SUBTROPICAL RIDGE. TY 19W WILL REMAIN IN A FAVORABLE ENVIRONMENT FOR THE EARLY PART OF THE FORECAST, SUSTAINING IT ABOVE 100 KNOTS/CAT 3 UNTIL ABOUT 48H, AT WHICH POINT LAND INTERACTION WITH TAIWAN WILL BEGIN TO WEAKEN IT. THE SYSTEM WILL WEAKEN TO 85 KNOTS/CAT 2 AS IT EXITS INTO THE TAIWAN STRAIT AROUND 72H. AFTERWARDS, INCREASING VERTICAL WIND SHEAR AND DECREASING SEA SURFACE TEMPERATURES WILL FURTHER WEAKEN THE SYSTEM TO 70 KNOTS/CAT 1 BY 120H.

TY 19W(CHANTHU).SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT SYSTEM WITH AN EYE-LIKE FEATURE THAT HAS WEAKENED SLIGHTLY OVER THE PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE-LIKE FEATURE IN ENHANCED INFRA-RED SAT IMAGERY. THE INITIAL INTENSITY IS BASED ON MULTI-AGENCY DVORAK INTENSITY ESTIMATES AND ADT WHICH ALL INDICATE THE SYSTEM IS CURRENTLY WEAKENING.

TY 19W(CHANTHU).MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT IN REGARDS TO THE RECURVATURE TRACK FORECAST SOLUTION WITH ONLY A 280 KM CROSS-TRACK SPREAD AT 120H. OF NOTE, OVER THE PAST 24 HOURS, THE MODELS HAVE WALKED THE TRACK EASTWARD IN THE LATER TAUS, MAKING IT MORE PROBABLE THE SYSTEM COULD IMPACT THE KOREAN PENINSULA OR MAINLAND JAPAN. THERE IS ALSO GOOD AGREEMENT IN THE INTENSITY GUIDANCE, AND THE FORECAST INTENSITY IS CONSISTENT WITH THE MULTI-MODEL CONSENSUS.

TY 19W(CHANTHU). HWRF AT 09/06UTC. INTENSITY GUIDANCE: 128KNOTS AT +0H.

INVEST 96W. AN AREA OF CONVECTION (INVEST 96W) HAS PERSISTED NEAR 17.0N 132.7E, APPROXIMATELY 1150 KM SOUTH-SOUTHEAST OF KADENA AB. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING CONVECTION OVER AN ILL-DEFINED LOW LEVEL CIRCULATION (LLC). A 090913Z SSMIS 91GHZ SATELLITE IMAGE REVEALS A POCKET OF DEEP CONVECTION DISPLACED TO THE SOUTH OF THE LLC, AND AN OVERALL LACK OF CONVECTIVE ORGANIZATION. INVEST 96W IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY WARM (30C) SEA SURFACE TEMPERATURES (SST) OFFSET BY MODERATE (15-25 KT) VERTICAL WIND SHEAR (VWS), AND WEAK OUTFLOW ALOFT. GLOBAL MODELS GENERALLY AGREE THAT 96W WILL DISSIPATE AS IT INTERACTS WITH STY 19W, WITH THE EXCEPTION OF GFS WHICH DEPICTS 96W TRACKING POLEWARD OF STY 19W AND CONSOLIDATING. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 10 TO 15 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1010 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS LOW.