Those do NOT occur regularly in the US at the same time (because the humidity peaks in the morning, but the temperature in the afternoon). Maybe in a few decades though.

35°C at 100% humidity is about the human survivability limit (at 6h exposure). This makes a lot of sense because humans generate ~100W of heat, but require their core temperature to stay constant-- if the environment is too hot and evaporation ineffective because of humidity, then your thermoregulation just breaks down and you die, just like from high fever.