How long will the UK heatwave last after sweltering 34°C forecast for today

Your fan – or, if you are lucky, your air conditioning – might have to be on for a little while longer.

Barely halfway into July, and the UK is about to enter its third heatwave this year.

The mercury has barely dropped below 15°C in some parts of the south this week, with health chiefs warning some people to ‘stay indoors’.

Lakes and reservoirs have dried up so drastically that a hosepipe ban has been introduced in Kent and Sussex.

But the Met Office says that few parts of the UK will see cooler temperatures, or even clouds in the sky, this weekend.

Forecasters expect today to reach as high as 34°C in south-east Wales, central southern England and west London.

Tomorrow won’t be any cooler, with a blistering 32°C forecast, which is good news for sunbathers and park-goers, at least.

Only Northern Ireland and Scotland will be cloudy at first, while those on the North Sea coast will feel a refreshing breeze.

Met Office Chief Meteorologist, Jason Kelly, said: ‘High pressure from the Atlantic will lead to a build in temperatures over the coming days, with heatwave criteria reached by the weekend. 

‘Whilst temperatures are expected to build day on day, becoming widely hot, they are unlikely to surpass those recorded at the start of the month.

This heatwave is expected to be longer-lived and extend further north and west into a larger part of the UK than previously seen this summer.’

Scotland will officially enter a heatwave over the weekend, Kelly said, adding that temperatures will ease slightly next week.

‘This hot spell is forecast to last longer and cover a broader area than previous ones so far this summer and pollen and UV levels will be very high in some areas,’ he said.

What is a heatwave?

Weather officials classify a heatwave as when an area sees at least three days of scorching temperatures, the same or over a particular threshold.

In Scotland, for example, a heatwave would be three days of 25°C or over. While in London, this threshold is slightly higher, at 28°C.

During the heatwave in June, for example, only larger parts of Wales and most of central and southern England experienced a heatwave. The rest of the nation did not, even if it still felt very toasty.

Meteorologist Alex Deakin said: ‘Every heatwave is different, every hot spell is different, and large parts of the UK haven’t experienced any heatwaves yet – only small areas have.’

When will the heatwave end?

The answer is still unclear, the Met Office says, though amber heat alerts issued by the UK Health Security Agency will end at 9am Monday.

The amber warnings – in effect in the East and West Midlands, East, South East and South West of England and London – warn that during the heat, there will likely be ‘a rise in deaths, particularly among those ages 65 and over or with health conditions’.

Thankfully, the Met Office says ‘there are signs that less hot, or fresher, conditions may arrive from the west early next week’.

‘But exactly how quickly this transfers eastward is uncertain,’ the weather service said.

‘It’s certainly possible that hot conditions may persist for a while longer, especially towards central, southern and eastern areas.’

Based on the Met Office’s threshold, London’s days-long heatwave will end Monday when temperatures reach what now seems to be a freezing26°C.

London will cool to 21°C by Tuesday before rising – once again to 26°C by Thursday, which is still below the heatwave definition.

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