Cloud cover, high humidity, and frequent afternoon thunderstorms driven by a persistent low-pressure band and enhanced southwesterly flow are the dominant factors capping Taipei’s August 25 maximum near 30–31 °C, the market’s leading outcomes. Official Central Weather Administration guidance and ensemble model guidance indicate a daytime range of 26–33 °C under mostly cloudy skies with a 60–70 % rain probability, limiting solar heating relative to clearer summer days. Recent active tropical moisture and the low-pressure system’s persistence have kept temperatures suppressed compared with climatological August averages of 32 °C. Traders are weighting the narrow spread between 30 °C and 31 °C because small shifts in thunderstorm timing or intensity—visible in the next GFS and ECMWF runs—could tip the daily peak by 1–2 °C before resolution.