**Trader sentiment for Seoul’s September precipitation centers on the 150-175 mm bin (42.5% implied probability), just above the 1991-2020 climatological average of ~142 mm.** This reflects a strong East Asian monsoon transition period when frontal systems and typhoon remnants typically deliver most rainfall, combined with a strengthening El Niño that historically modulates Western North Pacific typhoon tracks and can suppress or redirect late-season activity toward or away from the Korean Peninsula. Recent late-August heavy rains from a stationary front and anomalously warm Yellow Sea waters (29°C) have elevated short-term moisture availability, while the absence of direct typhoon landfalls through August leaves September vulnerable to late-developing systems. With ENSO models favoring a very strong event persisting through fall, traders appear to weigh reduced overall typhoon frequency against possible enhanced frontal rainfall, anchoring consensus near the upper end of normal variability.