This is something I haven't seen reported anywhere else. People don't really think of Tokyo and heat but apparently it's really hot there in the middle of the summer. Heat wasn't an issue in 1964 in Tokyo as the Olympics were held in October - not July and August like they will be in 2020.
"The 2020 Summer Olympics will take place in the midst of Tokyoâ€™s hot and humid summer period, possibly exposing athletes and visitors to the most challenging environmental conditions ever observed in the modern history of the Olympic Games. By illustrating observational data, this SPORTIFY CITIES report unambiguously demonstrates that, with maximum perceived or feels like temperatures regularly exceeding 45Â°C, the sheer scale and scope of the heat factor could greatly weaken an athleteâ€™s performance and increase the risk of heat stroke. "