Much of the UK is currently experiencing a spell of hot weather that feels distinctly more oppressive than heatwaves in recent memory. While the peak temperatures may not be breaking all-time records, the combination of meteorological factors at play is creating conditions that place significantly more stress on the human body. Understanding why this specific event feels worse requires looking beyond the headline temperature figure.
The primary reason for the heightened discomfort is elevated humidity. Meteorologists measure this using the dew point — the temperature at which air becomes saturated and water vapour condenses. When dew points climb into the high teens Celsius (around 16°C to 18°C or higher), the air feels “muggy.” During this current spell, dew points have frequently sat in that uncomfortable range.
High humidity cripples the body’s primary cooling mechanism: the evaporation of sweat. In dry heat, sweat evaporates rapidly, drawing heat away from the skin. When the air is already laden with moisture, evaporation slows dramatically or stops entirely. This leaves the body unable to regulate its core temperature effectively, leading to that sticky, suffocating sensation and a higher risk of heat exhaustion.
Compounding the daytime stress is the lack of nocturnal cooling. In many areas, overnight low temperatures have remained stubbornly high, often failing to drop below the high teens or low 20s Celsius. In urban centres, the “urban heat island” effect — where concrete and asphalt absorb heat during the day and release it slowly at night — keeps temperatures elevated further.
This prevents homes and bodies from recovering. Without a significant drop in temperature overnight, buildings retain heat, meaning indoor environments start the next day already warm. For vulnerable groups, particularly the elderly and those with underlying health conditions, this continuous heat load is the most dangerous aspect of a heatwave, as it disrupts sleep and accumulates physiological strain over consecutive days.
Adding to the misery is a lack of wind. Light winds mean there is little air movement to aid the evaporation of sweat or to flush hot air out of urban streets and homes. The air mass responsible for this weather has origins in the subtropics or the continent, bringing not just warmth but moisture drawn from the Atlantic or the near continent. This contrasts with heatwaves driven by hot, dry air from the Sahara, which often bring high temperatures but lower dew points, making the heat feel more bearable despite higher thermometer readings.
The practical implication is that the “feels like” temperature — often calculated as the heat index or humidex — is significantly higher than the actual air temperature. A temperature of 29°C with high humidity can impose the same physiological stress as 33°C or 34°C in dry air.
Standard advice remains vital but requires stricter adherence: stay hydrated before you feel thirsty, avoid physical exertion during peak hours (typically 11am to 3pm), and keep curtains closed on sun-facing windows. Crucially, check on neighbours or relatives who live alone, as the cumulative effect of sleepless, hot nights can creep up unnoticed. With climate projections indicating that humid heat events will become more frequent and intense in the UK, learning to manage these specific conditions is becoming a necessary life skill.
Image: Photo: shubh gupta · Pexels
Based on reporting from bbc.co.uk.
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