Persistent thunderstorm activity and high humidity across the Pearl River Delta are the main drivers keeping overnight lows near 26–28°C, as extensive cloud cover limits radiative cooling and maintains elevated dew points around 26–28°C. Subtropical monsoon patterns deliver frequent showers that suppress daytime heating but trap warmth at night, producing minimum temperatures close to the 25.4°C climatological average for the date. Ensemble model spreads reflect modest differences in expected cloud thickness and wind speeds from the southeast, which can shift the low by 1°C depending on timing of heaviest rain. Historical records show lows below 24°C require rare clear, drier intrusions absent in current guidance.