Trader sentiment for Hong Kong’s lowest temperature on May 20 shows tight clustering around 24–27 °C, each carrying 20–22 % implied probability, underscoring genuine short-range forecast uncertainty. Subtropical ridge positioning and moisture advection from the South China Sea are the dominant controls on overnight radiative cooling, while variable cloud cover and boundary-layer wind speeds introduce divergence among ensemble members. Hong Kong Observatory and global model runs currently differ by 1–2 °C on minimum temperatures because small shifts in timing of any weak frontal passage or convective activity can alter the diurnal range. Historical May climatology places typical minima near 25 °C, but the present synoptic setup allows for modest deviations above or below that baseline depending on how quickly the ridge strengthens. New model cycles over the next 48 hours will likely tighten these probabilities as the event window nears.