Thursday 25th June
The strong sunshine was relentless on Thursday, once again resulting in a maximum that broke the record set on the previous day. The peak of 33.9C was logged at 17.01, being a significant 13.1C above my long-term June average. The loss of equivalent rainfall, due to evaporation from plant life and the ground, was 5.9mm, whilst the UV strength was again High, not very far off Very High.
The past night was memorable in that the thermometer only dropped to 20.8C at 05.19 early Friday, which was 10.6C above average. This was the first ‘Tropical’ night during the heatwave, named as such as the minimum temperature did not fall below 20C. This overtook the previous record of 20.4C set in 2016.
Friday arrived with the sun a little muted after sunrise in Marlborough at 04.51, due to cloud on the eastern horizon, that had drifted in overnight from the North Sea over East Anglia. However, within an hour the sun had risen above the cloud, though still variable, and began to push the temperature upwards again.
There are subtle signs of a change in the not too distant future as the high slowly relocates towards eastern Europe as we approach the weekend. There is now confidence that this will result in the wind making a significant change in direction later on Saturday, to have a more westerly component, that will herald the fall away in peak temperatures to around or just above average for next week, bringing much relief. The lower temperatures will come with lower humidity.
High humidity prevents the body from cooling down
The hottest part of the UK saw the thermometer rise to 38 or 39C, and this becomes particularly uncomfortable when you factor in the humidity.
Humidity is a measure of how much moisture is in the air.
During hot weather our body controls our internal temperature by sweating and as the sweat is evaporated from our skin, it cools the air directly next to us, making us feel cooler.
If the air is more humid, the sweat from our skin cannot evaporate and cool us down as effectively as it would do if the air was dry.
Meteorologists can calculate therefore how the combination of air temperature and humidity feels – as a “feels like” temperature.
While the air temperature in past days was around 35C for example, it may actually “feel” more like it’s 41C due to the high humidity.
With temperatures nudging 40C, there have been some comparisons to the historic heatwave of July 2022 when the UK recorded 40C for the first time.
But during that heatwave the air was very dry. So, while headline temperatures were higher then, this June’s heatwave will feel hotter and potentially have more health impacts as a result of the humidity.