Seoul's September precipitation typically averages 140–190 mm based on long-term Korea Meteorological Administration normals, with the market favoring the 175–200 mm bin at 41.5% due to this climatological range amid declining but variable monsoon influences. The East Asian monsoon front weakens through the month, while residual moisture from a persistently warm Yellow Sea and potential late-season typhoons or tropical systems can boost totals. Recent late-August heavy rains exceeding 200 mm in parts of central and southern Korea reflect enhanced convective activity from warm sea-surface temperatures, which may carry forward into early September. Model consensus points to moderate rainfall on 8–10 days, keeping outcomes near historical baselines without strong signals for extremes.