01 What is the Heat Index?

https://en.wikipedia.org/wiki/Heat_index

The Heat index refers to the perceived temperature based on the measured air temperature and relative humidity.

The heat index is a value used by US meteorologists to describe the influence of the measured air temperature and humidity on the human body.

26–32 °CCaution: fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps.
32–41 °CExtreme caution: heat cramps and heat exhaustion are possible. Continuing activity could result in heat stroke.
41–54 °CDanger: heat cramps and heat exhaustion are likely; heat stroke is probable with continued activity.
over 54 °CExtreme danger: heat stroke is imminent.