**Latest forecasts from global and regional models, including GMS data and agency guidance, show Seoul and Incheon reaching a daily maximum of 21°C on October 3 under mostly cloudy skies with light southeasterly winds and minimal precipitation risk.** This outcome aligns with observed afternoon readings stabilizing near that level amid autumn transitional conditions, where daytime heating is moderated by cloud cover and typical October baseline temperatures. Traders assign near-certain probability to 21°C because multiple independent model runs and real-time observations converge tightly on this value, with little scope for rapid shifts this late in the day. Only an unexpected late surge in insolation or localized measurement variance at the official station could realistically alter the recorded high, though current atmospheric stability makes such deviations unlikely.