Is it good to work out when the day will reach up to 100 degrees?

It’s going to be a scorcher here in San Diego this up coming week. Two weeks ago we reached 90 degrees and I would work out in the morning, a 3 mile walk. I was so fatigue in the afternoon, I did my work out around 9–10am. I drank water all day but still felt fatigue.

How should I keep my little guy cool? He has therapy sessions throughout the day all week should I cancel them this week? We don’t have air conditioning & he was grumpy as heck the other week.