Final answer:
The heat index is a measure that combines air temperature with relative humidity to indicate how hot the air actually feels to the human body, which is particularly significant in summer months when high humidity can create hazardous heat conditions.Option 3 is the correct answer.
Step-by-step explanation:
As reported by the National Weather Service, the heat index relates temperature and relative humidity, which indicates how hot the air feels due to the humidity. The heat index, or 'feels-like' temperature, is a measure that combines the air temperature with the relative humidity to determine the human-perceived equivalent temperature.
Because high humidity hinders the evaporation of sweat from the skin, the body feels warmer on humid days. The heat index is a critical measure that helps individuals understand how weather conditions might affect their bodies differently than what the actual air temperature suggests.
On a hot day, if the relative humidity is high, the high moisture content of the air reduces the effectiveness of the body's natural cooling mechanism through evaporation.
This is why relative humidity plays a significant role in how hot the weather feels and can create dangerous conditions like heat exhaustion or heat stroke during heat waves. It is especially important during summer months, not winter months, and it is not related to air pressure or the effects of wind on the skin.