[zaarn]

Humidity is the real killer. You can easily handle temperatures above 60C as long as the air is bone dry.

It's not 100% humidity, it's a flowing scale that depends on how much cooling you need to do via sweating.

If it's 10C outside, you don't need any sweating at all and the air humidity doesn't matter.

If it's 30C outside and 50% humidity, you're going to feel miserable, older folks could suffer under the stress.

From my experience, keep the sum of humidity in % and temperature in C below 100, better 80, to be comfortable.