Recent numerical weather prediction runs from global models indicate clear skies and light southerly flow over Busan on September 30, supporting afternoon highs near 26–27 °C. Radiative warming under minimal cloud cover, combined with warm sea-surface temperatures in the Korea Strait, favors the upper end of typical late-September values, while modest northeasterly drainage overnight keeps minimums from elevating the daily maximum. Ensemble spread remains narrow, with only modest differences in boundary-layer mixing and exact wind direction creating the tight contest between 27 °C and 28 °C outcomes. The Korea Meteorological Administration’s next update and final model cycles before market close will provide the decisive observational guidance for traders.