Persistent rain and cloud cover from a low-pressure system are limiting nighttime radiative cooling in Taipei, keeping forecast lows clustered around 24–26°C for September 4. Multiple model runs show high humidity, light variable winds, and widespread showers or thunderstorms through the period, which reduce the typical diurnal temperature drop. Central Weather Administration guidance and ensemble outputs indicate only modest overnight cooling under these conditions, producing the tight market spread between 24°C, 25°C, and 26°C outcomes. Minor differences in precipitation timing or intensity could shift the exact minimum by 1°C, sustaining trader uncertainty until updated model guidance or observations arrive closer to the date. Historical September baselines near 23–24°C provide context but are being exceeded due to the current unstable pattern.