Trader sentiment for Seoul’s September precipitation strongly favors drier-than-average outcomes, with <75 mm leading at 39% implied probability amid a high-pressure ridge dominating the Korean Peninsula. Historical normals from the Korea Meteorological Administration place September averages at 128–141 mm, driven by the retreating East Asian monsoon and occasional typhoon influences. As of early September 2026, Seoul has recorded mostly clear skies and negligible rainfall, with any precipitation confined to the east coast and Jeju due to strengthened easterlies and distant tropical systems like Typhoon Krovan. Short-term ECMWF and KMA ensemble guidance indicate continued suppression of convective activity, though late-month variability from shifting steering patterns or residual moisture could still add 50–100 mm. This setup explains the market’s tilt toward the lowest bin while leaving room for upside surprises if models shift.