Heat Index

The Heat Index is one of the most useful composite weather measures, especially for gauging human comfort and safety in warm conditions.

Here’s a concise breakdown:

🔹 What It Is

The Heat Index (HI) combines air temperature and relative humidity to represent how hot it actually feels to the human body. High humidity reduces the body’s ability to cool itself by sweating, so the perceived temperature rises.

🔹 Example

Air Temp	Humidity	Feels Like (Heat Index)
30 °C	40 %	31 °C
30 °C	70 %	36 °C
35 °C	60 %	45 °C

🔹 Interpretation

Heat Index (°C)	Level	Effect
< 27	Comfortable	Normal activity fine
27–32	Caution	Fatigue possible with long exposure
33–41	Extreme caution	Heat cramps and exhaustion possible
42–51	Danger	Likely heat exhaustion or stroke
> 52	Extreme danger	Serious risk of heat stroke

🔹 Why It Matters

• Helps assess outdoor work, sport, or observing safety.
• More realistic than air temperature alone.
• Many weather monitors automatically calculate it if they measure temperature and humidity.