Humidity: it’s all relative
What does '90 percent humidity” really mean? Try thinking of water vapour as something that cohabitates with dry air; water vapour becomes more prevalent as winds bring it in or lakes and oceans evaporate more of it The warmer the dry air is, the more water vapour can coexist with it, which is where the “relative” in relative humidity comes in. Many describe this process as the air “holding” moisture, although sticklers disapprove of the linguistic convenience. If the air is cooled past a certain point, some of the vapour in it must condense – like the droplets that cling to an icy glass on a hot day. Air only needs to warm up by about 11°C/20°F in order to hold roughly twice as much water vapour. In other words, air at 21°C/70°F can hold nearly double the moisture of air at 10°C/50°F. A relative humidity of 90 percent means that you're getting 90 percent of all the water vapour that can exist at the current air temperature. Of course, this level of humidity feels much worse on a hot day than when it's frigid. That's why meteorologists prefer to use something called the dew point, a temperature-like value that serves as an absolute measure of how much water vapour is in the air. If you cool air down to its dew point, the relative humidity is, by definition, 100 percent A dew point of 15°C/59°F feels only mildly humid, while most people would consider a dew point of 25°C/79°F extremely muggy, regardless of the relative humidity. Once dry air warms to above 32°C/90°F, it can coexist with a vast amount of water, so much that it never gets saturated under everyday conditions. You may hear somebody tell you that they sweated through 95 degrees [F] and 95 percent humidity”. Such an extreme would not only be intolerable, it's virtually impossible. Some of the world's most oppressively humid regimes would be hard-pressed even to reach 32°C/90°F while maintaining 90 percent RH.