I commute year round in Phoenix. The highest temp was 117°F a few years ago. Hot? Sure. But as others have said it's a dry heat. Plus my commute is only 5 mi one way.
If you just keep commuting every work day you become acclimated as the year goes along. Both to the highs and the lows. Are there limits? Yep. But we're capable of more than we think sometimes.