**Forecast consensus points to a Guangzhou overnight low near 25–26°C on September 17, driven by typical late-summer subtropical conditions with light southerly winds, moderate humidity, and partly cloudy skies that limit strong radiative cooling.** Multiple models show highs near 32–34°C transitioning to nighttime lows of 25–27°C, consistent with the September climatological average low of ~24°C. The closely matched market probabilities (20°C or below and 30°C or higher both near 37%, 26°C at 34.5%) reflect genuine uncertainty in exact overnight minimums. Key differentiating factors include variable cloud cover—clearer periods enhance longwave radiative heat loss from the surface, while scattered showers or higher humidity reduce cooling rates—and minor steering influences from regional pressure gradients. No major synoptic systems (e.g., typhoon remnants or cold fronts) are indicated to shift temperatures outside the mid-20s range before resolution.