Humidity: Feeling the heat on warm sunny days

Humid weather can make us feel uncomfortable during the summer months.
Humid weather can make us feel uncomfortable during the summer months. Photo: PA

By Becky Mantin: ITV Weather Presenter

Hands up if you have felt irrationally irritable on some of our recent warm sunny days!

Despite the beautiful sunshine that bathed much of the UK in wonderful summery weather in recent weeks, occasional high humidity makes it, for many, an uncomfortably time of year.

The culprit? Humidity – the term used to describe the measurement of the amount of water vapour in the air.

Split into three types; absolute, relative and specific, when the term 'humidity' is used in a TV weather forecast, it typically refers to ‘relative’ humidity.

Scientifically put, relative humidity is a measurement of the water vapour content of the air relative to how much water vapour could be held at the current temperature.

As the air can only hold a limited amount before it results in the formation of clouds, fog or precipitation, humidity can have a big influence on the types of weather that will form.

None of us are surprised, for example, when a sultry, humid day culminates in a mighty thunderstorm.

Humid air can result in thunderstorms.
Humid air can result in thunderstorms. Credit: PA

From the point of view of you and me however, relative humidity is how the weather ‘feels’.

Our body temperature is inherently dependent on the air as it wicks moisture away from our skin.

Humans are hugely dependent on our ability to sweat as a way of regulating body temperature.

If relative humidity is high, the amount of moisture that evaporates from our skin (that is, our ability to sweat) is limited so we feel warmer and stifled – you might hear people grumbling about the day feeling ‘close’ or ‘sticky’.

Conversely, if relative humidity is low it can feel colder than it actually is as moisture is readily removed from our skin thus lowering our body temperature.

In the winter, this is often when people may remark that ‘it feels too cold too snow’ when what they actually mean is that it feels ‘too dry to snow’ and, in some circumstances, they may be right!

Whilst humidity varies on a daily basis, some areas around the globe are generally more humid than others.

Since warmer air can hold more water vapour than cooler air, countries nearer the equator tend to have a higher humidity. Unsuprisingly, here in the UK, humidity is often higher at the coast thanks to the close proximity of the sea.

Measured on a local scale using a hygrometer and recorded in terms of a percentage (any level above around 60/70% is considered high), the effect of relative humidity on our day to day lives is less easy to measure beyond how it ‘feels.'

Asthma and hayfever sufferers feel the conditions more than others.
Asthma and hayfever sufferers feel the conditions more than others. Credit: PA

Although some asthma sufferers complain of a increased respitory problems in times of high humidity.

Those prone to headaches often find that spells of hot, humid weather can bring on head pain with many medical experts believing such conditions trigger temporary chemical and electrical changes in the brain that in turn, irritates nerves, leading to a headache.

Whilst we can’t control the weather, at least having an understanding of its effect on us gives us a greater chance of being prepared for the fall out!