UK Heatwave 2026: Why Humidity Made It Unbearable

3 minute read

The UK has just come through one of the most intense heat events ever recorded in history. Temperatures at Santon Downham in Suffolk hit 37.3°C on the 26th of June breaking the June record for the third consecutive day. If you were outside during the peak of the heatwave, you already knew something was different about this one. Strangely, it felt more suffocating than the 40.3°C record set at Coningsby in 2022; the difference is the humidity. 

Temperature Tells You Half the Story

When we talk about heat, we focus only on what the number on the thermometer says, but that temperature reading alone does not tell you how your body is going to cope.

A human body regulates temperature by sweating. As sweat evaporates from the skin, it carries heat away with it. When the air is already heavily loaded with moisture, that process slows down. Sweat sits on the skin rather than evaporating, your core temperature climbs faster, and heat stress sets in more quickly.

This is why the Met Office highlighted humidity as the defining feature of the June 2026 event. Dew points, which is the measure of how much humidity is in the air, reached approximately 22°C during the peak on Friday the 26th of June. 

What Is Relative Humidity, and Why Does It Matter?

Relative humidity (RH) expresses how much moisture the air holds as a percentage of the maximum it could hold at that temperature. At 100% RH, the air is fully saturated and evaporation stops entirely.

A rough guide to how RH affects comfort:

• Below 30% RH- Very dry. Skin and airways feel parched, but the body cools efficiently.
• 30-60% RH- Generally comfortable. The standard target range for indoor environments.
• 60-70% RH- Noticeably muggy. Sweating becomes less effective.
• Above 70% RH- Oppressive. Cooling through perspiration is significantly impaired, especially when temperatures are also high. 

During the June 2026 heatwave, many parts of southern and central England were sitting above 70% RH during the daytime heat, with tropical nights where temperatures did not drop below 20°C.

How a Wet and Dry Bulb Hygrometer Works

The most precise traditional method for measuring humidity uses two thermometers side by side. One with a dry bulb, and one with the bulb wrapped in a water-soaked wick. As air passes over the wet bulb, evaporation cools it. The drier the air, the more evaporation occurs and the greater the difference between the two readings. Cross-referencing those two temperatures against a set of tables gives you relative humidity.

Our ClimeMET CM3505 Masons Wet and Dry Bulb Hygrometer uses exactly this principle a method that has been trusted in meteorological stations and professional monitoring for well over a century. If you prefer a digital readout, the TFA Digital Thermometer/Hygrometer and TFA Digital Min/Max Thermometer/Hygrometer both display temperature and humidity simultaneously, with min/max memory so you can track how conditions fluctuate through the day and night.

Tips for Staying Cooler When Humidity Is High

Monitoring humidity is useful but acting on what you know is better. If RH in and around your home is creeping up during a heatwave, here is what makes a practical difference:

Keep air moving, not just circulating hot air. A fan in still, humid air pushes warm moisture around you without doing much good. Position fans to draw cooler air in from the shadiest side of the building typically early morning before the fabric of the building heats up and close windows and blinds during the hottest part of the day to trap cooler air inside.

Cross-ventilate at night. Once outdoor temperatures drop below indoor temperatures (your thermometer will tell you when), open windows on opposite sides of the building to create a draft. On a tropical night like those during this heatwave, this window may be brief or non-existent but when it opens, use it.

Reduce indoor moisture sources. Cooking, showering and drying laundry indoors all add water vapour to the air. During a high-humidity heatwave, use an extractor fan or dry laundry outside to avoid pushing indoor RH higher than it needs to be.

Hydrate consistently, not reactively. When sweat does not evaporate, you may not notice how much fluid you are losing. Drink water steadily through the day rather than waiting until you feel thirsty.

Monitor a shaded outdoor reading. The temperature in your garden in the shade gives you better information about conditions than the headline figure from the nearest weather station, which may be miles away. Our Fischer Scientific H7 Hair Hygrometer is rated to handle the full range of outdoor conditions and gives accurate readings across the complete humidity scale.

More Heat Is Coming

The long-term picture is straightforward. Events like this are becoming more frequent and more intense. The UK has now seen record-breaking May heat and record-breaking June heat in the same year. Understanding the conditions around you has become more important than ever. 

Our full hygrometer collection covers everything from traditional wet and dry bulb instruments to digital stations. Wherever you want to monitor conditions at home, in the garden, or even in a greenhouse, we'll be sure to have an instrument suited for you.