Persistent heavy rain and cloud cover from Typhoon No. 25, which is forecast to approach the Kanto region on September 21, represent the dominant driver keeping Tokyo’s daytime maximum near 25–26°C. Official Japan Meteorological Agency guidance and multiple model runs project widespread precipitation, high humidity above 90 percent, and northeasterly winds that limit surface heating and reduce the diurnal temperature range. These conditions suppress the potential for temperatures to reach 27°C or higher while also preventing a drop below 24°C in most ensemble members. Trader consensus reflected in the closely matched 24–26°C probabilities captures remaining uncertainty in exact timing of heaviest rain bands and localized wind shifts that could briefly alter observed maxima at official stations. Updated JMA and global model runs over the next 12–18 hours will provide the clearest signals for final resolution.