Phew! Going outdoors is like being in a sauna

Residents take advantage of the low humidity for a pleasant stoll on Kite Beach in Dubai earlier this week. Tom Dulat / Getty Images

ABU DHABI // Signs that the season is changing – your glasses mist up, the shirt sticks to your back or your hair goes all frizzy.

But what exactly does 100 per cent humidity, forecast at times this week, actually mean?

Well, at any given temperature, there is only so much water vapour the air can hold. When the maximum is reached, which occurs often in the UAE, humidity is considered to have reached 100 per cent.

Weather forecasters measure the relative humidity, a measurement of how close the air is to being saturated. This is the world’s most common measure of humidity.

“It is a relationship between temperature and water vapour in the atmosphere,” said an expert at the National Centre of Meteorology and Seismology.

“There is a variation in relative humidity to temperature. If the temperature increases, the relative humidity decreases because the ability to hold water is higher, and vice versa.”

The relative humidity changes as temperature does, which is why at night the relative humidity is usually higher.

“At night, relative humidity increases because the temperature is lower but humidity is higher,” the expert said. “In the summer it is often 100 per cent.”

Relative humidity gives residents a better idea of how the weather will feel, according to the UK Meteorological Office.

High relative humidity is uncomfortable in warm temperatures because the saturated air affects the body’s cooling mechanisms. Air cannot easily contain any more water as a vapour, so it cannot effectively evaporate the sweat from our skin, the Met Office said.

Algorithms on websites such as Accuweather.com consider factors such as humidity to give users a better understanding of what the weather will feel like.

On Wednesday, the website said it was 31°C in the UAE but that it “felt like” 41°C. In summer, for example, a slight breeze in summer equates to a -1°C modifier, while 100 per cent humidity might add 5°C to the real feel.