June temperature records are poised to be shattered this week as England and Wales are gripped by the year's second major heatwave. Temperatures are expected to climb into the mid- to high 30s Celsius, mirroring the intensity of a previous heat event in May. However, for many, the current conditions will feel considerably more oppressive, with a 35C forecast potentially feeling like 41C.

This amplified sensation of heat is attributed to a confluence of factors, primarily an "unrelenting heat dome," elevated humidity levels, and a series of "tropical nights" where temperatures fail to drop significantly after sunset. These elements combine to create a more challenging environment for the body's natural cooling mechanisms.

Dr. Akshay Deoras, a senior research scientist at the University of Reading, explained that the "heat dome" – a large, static area of high pressure – is the primary driver. This weather pattern causes air to sink, compress, and heat up as it nears the ground. Crucially, this sinking air also tends to be dry, limiting cloud formation and allowing intense solar radiation to heat the surface further.

Unlike the May heatwave, where the heat dome's center was directly over the UK, this week's event has a different origin. The current heat dome originated in the hot and humid subtropics and has been centered over France, where temperatures have already reached the 40s Celsius. As it has shifted slightly northward and eastward, it has created a south-easterly airflow that is drawing hotter, moister air into the UK, significantly increasing humidity.

High humidity levels hinder the body's ability to cool itself through sweating. Normally, as sweat evaporates from the skin, it cools the immediate surrounding air. However, when the air is already saturated with moisture, sweat evaporates less efficiently, reducing the cooling effect and increasing the perceived temperature. Meteorologists calculate a "feels like" temperature to account for this combined effect of air temperature and humidity.

While the headline temperatures might not consistently surpass the record highs of July 2022, the presence of high humidity means this heatwave could feel hotter and potentially pose greater health risks. The 2022 event, though reaching 40C, was characterized by much drier air, offering a different kind of heat stress.

Experts have described the current situation as a "heat-dome driven furnace" that will affect much of southern England and push temperatures into "truly exceptional territory." The prolonged periods of high night-time temperatures, known as tropical nights, will offer little respite for many residents, contributing to overall discomfort and potential health impacts.

Further analysis of the situation will likely focus on the long-term implications of such humid heat events, comparisons with international heatwave patterns, and the effectiveness of public health measures in mitigating the risks associated with extreme heat and humidity.