**Trader sentiment for Seoul's October 2026 precipitation reflects a closely contested market favoring drier outcomes, with <20 mm and 30–40 mm bins tied at 19.5% implied probability.** A strengthening El Niño event, with Niño-3.4 anomalies exceeding +2°C, typically suppresses rainfall across parts of East Asia during the autumn transition by altering the East Asian jet and reducing moisture transport. Historical normals place October totals near 50–70 mm from frontal passages averaging one per week, but recent dry summer conditions, absent typhoon landfalls, and an early-October trough delivering only modest rain (5–10 mm in Seoul) support lower expectations. Cold air advection following the front further favors clearer, drier periods. Variability in frontal timing and any late-month disturbances introduces uncertainty, keeping higher bins like 85 mm+ at just 14.5%.