**Persistent low-pressure trough and associated thunderstorm activity are the main drivers suppressing Hong Kong's daytime maximum on August 25.** A broad trough over the northern South China Sea and Guangdong coast continues to deliver scattered showers and thunderstorms, with Hong Kong Observatory guidance indicating multi-cloud conditions, periods of heavy rain, and south to southwest winds of 4–5 (gusts to 6) that enhance mixing and limit surface heating. This pattern favors highs near 29–30 °C rather than the 31–32 °C that would occur under clearer subtropical summer conditions. High relative humidity (80–95 %) and cloud cover further reduce insolation, while the timing and intensity of convective cells introduce short-term variability that keeps the precise peak uncertain. Recent model runs and official outlooks show only modest day-to-day changes, but any delay or weakening of the trough could allow brief clearing and a rebound toward 31–32 °C; conversely, stronger or more widespread storms would cap readings closer to 29 °C or below. With the market’s top probabilities clustered tightly around 30–31 °C, traders are pricing in this narrow range of outcomes amid genuine forecast spread on storm evolution over the next 48 hours.