For instance, right now on the east coast the heat and humidity have been killer. If I were to go to the other side of the US, to the west coast, why does the temperature feel much more tolerable?
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High humidity makes the air saturated with water, thus the sweat from your skin will not evaporate as easily. When your sweat cannot evaporate properly, your body will have problems to cool itself.
Your body’s ability to regulate its temperature in high heat relies on sweat. Sweat lowers your body temperature by evaporation, which removes heat from your body. Sweat evaporates more easily when there is less moisture in the air, or low humidity. High humidity prevents efficient evaporation, and sweat will drip off you instead.
So there is some validity to the adage “it’s not the heat, it’s the humidity.”
When sweat evaporates it cools us down. Higher humidity slows down the evaporation, and therefore the cooling
In addition to what other says, water (and water vapor) has very high thermal capacity. Therefore both hot and cold humid air feels hotter or colder than arid air at same temperature.
Your body gets rid of heat by sweating. But it’s not the sweat itself that cools your body; it’s the sweat evaporating into the air. Like any other liquid that evaporates into a gas, sweat requires heat to evaporate, and it gets that heat from your body. The sweat pulling heat from your body and evaporating is what cools you down.
If the humidity is high, your sweat doesn’t evaporate into the air as easily. Less sweat evaporating means less heat being pulled from your body, which makes it harder for your body to cool down. The humidity makes the temperature feel hotter because your body is not able to cool itself as effectively.
This is why it is so dangerous to do intense outdoor activities during period of high heat and humidity. Your body can’t get rid of enough heat in high humidity, so the heat builds up and can lead to a dangerous heat stroke.
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