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My hygrometer says that the humidity is 65% in Victoria, but the temperature is a very pleasant 26° C (which I think is about 80° F in the obsolete system still used in certain backward regions of the world).
The humid feel of the atmosphere is relative to the temperature, hence the term "relative humidity". The capacity of air to hold moisture goes up with the temperature and down with the temperature. To compare relative humidity levels between localalities, it is best to do so either at the same temperature, or at the warmest part of the day.
When the relative humidity is low, water evaporates more quickly. When water evaporates, or changes from a liquid state to a vapor, it absorbs a great deal of energy. To raise the temperature of one gram of water by one degree Celsius requires the addition of one calorie of energy. To change water to vapor, without raising its temperature, requires 540 calories. This is why evaporating water cools things off.
The human body cools itself by sweating, which requires that the sweat evaporates and removes heat from the body at the 540 calories per gram rate. If the relative humidity is high, the rate of evaporation is lessened, and one feels uncomfortably warm, being unable to transfer heat quickly and efficiently to the atmosphere. This is also why swamp coolers don't work well when the relative humidity is high.
Bored yet?
