**Forecast uncertainty in short-term numerical weather models is the main driver behind the near-even split between 15°C-or-below and 25°C-or-higher outcomes for Busan’s minimum temperature on September 25.** Global and regional models (including GFS and ECMWF runs) currently indicate an overcast to mostly cloudy regime with northeast winds of 5–11 mph and a chance of light rain or showers, which would limit nighttime radiative cooling and support overnight lows near 21–22°C. However, modest shifts in cloud timing, precipitation coverage, or a slightly stronger high-pressure influence could allow clearer intervals and greater cooling toward the mid-teens, while persistent marine influence or delayed frontal passage could keep readings higher. Late-September climatology shows typical daily minima around 17–19°C, but the current warmer pattern and model spread create genuine divergence on whether the day’s low falls into the cooler tail or stays elevated, keeping the two headline bins nearly tied at roughly 50% and 49% implied probability.