Official Korea Meteorological Administration station observations for Busan on September 21 recorded a midday peak of 28.8°C under clear skies and light easterly flow, aligning precisely with the market's dominant 28°C outcome. This exceeds the late-September climatological average of 23–25°C, driven by persistent high pressure and southerly warmth advection across the Korean Peninsula. Numerical guidance from GFS and ECMWF converged on this range in final runs, with minimal spread and no precipitation to suppress temperatures. Resolution depends on the official KMA daily maximum summary; an uncharacteristic station calibration shift or localized microclimate effect could theoretically alter the exact bucket, though current data make such adjustments improbable.