**Trader sentiment for the highest temperature in Seoul (Incheon) on August 21, 2026, clusters tightly around 27–29°C (combined ~78% implied probability), reflecting the Korea Meteorological Administration (KMA) short-range forecast of a 29°C maximum under mostly cloudy skies with afternoon rain chances of 30–60%.** This outlook follows an earlier August heatwave that produced peaks near 39°C in Seoul but has given way to more typical late-summer conditions, with increased cloud cover and moisture limiting intense daytime heating. Key scientific drivers include the balance between residual warm, humid air masses and incoming cloud/rain systems that reduce incoming solar radiation and promote evaporative cooling. Incheon’s coastal location adds a moderating marine influence compared with inland Seoul stations. Minor odds spreads among 27°C, 28°C, and 29°C outcomes stem from uncertainty in exact rain timing, model differences in boundary-layer mixing, and the narrow window for peak temperature measurement (typically 9 AM–5 PM local time). Historical August averages near 28–31°C provide context, while proximity to resolution leaves limited room for major forecast shifts absent an unexpected clear-sky surge or stronger frontal passage.