UK health officials have upgraded their warning for the escalating heat as southern England will experience an official heatwave this week, forecasters have confirmed. Temperatures are on the rise for much of the UK, most likely peaking on Wednesday and Thursday with 32C expected across parts of the south and south-east, the Met Office said. There is also a chance the highest temperature of the year so far of 32.2C on 10 June could be exceeded this week, most likely in south-east England, where the temperature in one or two places could reach 33C, the forecaster said. The UK Health Security Agency, which provides alerts for the health and social care sector in England, has issued an amber heat health alert, which highlights increased risks to those more vulnerable to heat. The public health body had initially issued a yellow heat health alert for all of England, apart from the north-east. However, this has now been increased to amber from midday on Tuesday until 9pm on Sunday. An analysis by Climate Central, a US research group, found that human-caused climate breakdown had made the heatwave at least five times more likely to happen across most of the UK. The analysis found that six major cities – London, Leicester, Coventry, Leeds, Sheffield and Birmingham – were forecast to have sustained temperatures more than 10C above average for the time of year. Friederike Otto, senior lecturer in climate science at the Grantham Institute, said: “This week’s heat in the UK has been made hotter by climate change that is the result of human activities like burning coal and other fossil fuels. This is now the case for every heatwave, everywhere in the world. Until net greenhouse gas emissions end, heatwaves in the UK and elsewhere will continue to become hotter and more dangerous.” The Met Office chief meteorologist, Neil Armstrong, said: “High pressure is situated to the south-east of the UK, which is bringing more settled conditions and temperatures well above average for the time of year. “While the highest temperatures are expected in the south, heatwave conditions are likely across much of England and Wales especially, with parts of Scotland and Northern Ireland also likely to see some unseasonably high temperatures. “An active tropical cyclone season in the north Atlantic has helped to amplify the pattern across the north Atlantic, pushing the jet stream well to the north of the UK, allowing some very warm air to be drawn north. It’s a marked contrast to much of the meteorological summer, when the UK was on the northern side of the jet stream with cooler air and more unsettled weather.” In addition to high daytime temperatures, which could result in official heatwaves from as early as Tuesday in some spots, it will remain uncomfortably warm overnight, especially in the south, with a chance of “tropical nights”, which is when overnight temperatures remain in excess of 20C, the Met Office said. The highest overnight minimum temperature for September on record is 21.7C, and this record could be threatened on Wednesday and Thursday nights in particular. While the heat will probably peak on Wednesday and Thursday, temperatures and humidity will remain high for many in the south into the weekend, and there’s an increasing chance of some intense thundery downpours, most likely in the west. The Met Office’s deputy chief meteorologist, Steven Keates, said: “A cold front will begin to influence things from the north-west towards the weekend, though it’ll remain very warm or hot in the south. “There’s a chance the thunderstorm risk to western areas from Friday onwards may require a warning response, with some potentially impactful downpours, though exact details on the likely positioning of these downpours are still being determined.” The UKHSA said “increased mortality” across the population was likely, especially among those aged 65 or above and those with health conditions. It also said temperatures in care settings could exceed the recommended threshold for clinical risk assessment.