June temperature records are set to be broken this week as the second heatwave of the year grips England and Wales. Temperatures are expected to reach the mid- to high 30s Celsius, similar to May's heatwave, promising several uncomfortable days and nights. However, for many, the perceived heat will be significantly amplified, with a forecast of 35C potentially feeling like 41C due to a combination of an unrelenting heat dome, high humidity, and consecutive tropical nights.

The driving force behind this intense heat is a large, static area of high pressure, commonly known as a heat dome. This phenomenon causes air to sink, compress, and heat up as it reaches the ground. The sinking air also dries out the atmosphere, preventing cloud formation and allowing strong sunshine to further heat the surface. Unlike the May heatwave where the heat dome was centered over the UK, allowing heat to build internally, this week's event originates from the hot and humid subtropics and is centered over France, where temperatures have already soared into the 40s Celsius. As this system shifts northward and eastward, it draws hotter, moister air into the UK via a south-easterly airflow, significantly increasing humidity and heat stress.

Dr. Akshay Deoras, a senior research scientist at the University of Reading, described the situation as a "heat-dome driven furnace" that will push temperatures in southern England and parts of Wales into "truly exceptional territory," with highs of 38-39C expected. The high humidity is a critical factor in the increased discomfort. Humidity measures the amount of moisture in the air. During hot weather, the body cools itself by sweating, and the evaporation of sweat from the skin cools the immediate surroundings. However, high humidity inhibits this evaporation process, making it harder for the body to regulate its temperature and leading to a higher "feels like" temperature.

While the air temperature may reach 35C, the elevated humidity can make it feel as warm as 41C. This distinction is crucial when comparing the current heatwave to the historic one in July 2022, which saw the UK record 40C for the first time. Although the headline temperatures were higher in 2022, the air was very dry, allowing for more effective body cooling. This June's heatwave, despite potentially lower peak temperatures, will likely feel hotter and could have more significant health impacts due to the moisture in the air.

The prolonged periods of high night-time temperatures, known as tropical nights where temperatures do not fall below 20C, will offer little respite for many. This continuous exposure to heat, without the cooling effect of the night, exacerbates the physical and mental strain on individuals.

Experts warn that the combination of extreme daytime heat and stiflingly warm nights poses a significant public health challenge. The body's ability to recover from heat stress is compromised, increasing the risk of heat-related illnesses, particularly for vulnerable populations such as the elderly, young children, and those with pre-existing health conditions.

The implications of such prolonged and intense heatwaves extend beyond immediate health concerns, impacting infrastructure, agriculture, and energy demand. The consistent need for cooling, whether through air conditioning or other means, places a strain on power grids.

As the heatwave continues, authorities are urging the public to take precautions, stay hydrated, and check on vulnerable individuals. The recurring nature of these extreme weather events underscores the growing impact of climate change and the need for adaptation strategies.