BBC News
Darren BettLead Weather Presenter
PA MediaAmber heat health alerts have been issued for parts of England as temperatures are set to climb to more than 30C.
They will be in force from 12:00 BST on Friday until 18:00 BST on Tuesday, with the warmest weather expected on Sunday and Monday.
The amber alerts will be in place for five regions - East Midlands, South East, South West, East and London - while less serious yellow heat health alerts will be in force for two areas, Yorkshire and Humber and the West Midlands.
The UK Health Security Agency (UKHSA) warns that the hot weather is likely to bring increased pressures on health and social care services.
The new heat health alerts come as a second heatwave of 2025 is expected in parts of the UK. The first heatwave saw this year's hottest day recorded - 33.2C in Charlwood, Surrey on 21 June.
Scotland and Northern Ireland will only have temperatures up to around 22C in the coming days but England and Wales will be much hotter.
The heat will start to build in East Anglia and South East England on Friday with temperatures reaching 27C.
Temperatures will continue to rise into the weekend with the heat spreading to all but the far west of England and Wales and the far north of England. In the Midlands, Lincolnshire, East Anglia and South East England the temperature will quickly reach 30C or more.
The peak of the heat is expected to be on Monday when a temperature of 34C or 35C could be reached around London or Cambridge.
The weather will also become humid again which will make the heat feel more uncomfortable, including at night.
Parts of the country could see a 'tropical night' on Sunday and Monday - a term used to describe a night when temperatures do not fall below 20C.
Met Office criteria says a heatwave is reached when locations reach a particular threshold temperature for at least three consecutive days.
That varies from 25C across the north and west of the UK, to 28C in parts of eastern England.
The UKHSA alert system works in conjunction with the Met Office but has a focus on health risks in a bid to provide early warnings for health and government services.
There are four levels of warning - green, yellow, amber and red - an amber warning means the whole health service is likely to be affected by the hot weather.
Among examples given by UKHSA are difficulties managing medicines, the ability of the workforce to deliver services and internal temperatures in care settings exceeding the recommended thresholds.
The agency also refers to a possible rise in deaths - particularly among those aged 65 or over or with health conditions - as well as health risks to the wider population.
Temperatures are forecast to fall on Tuesday although some parts of England will remain in heatwave territory - with temperatures of near 30C expected in East Anglia and South East England.
The residual heat could trigger thunderstorms on Tuesday night.
The possible heatwave coincides with some major events taking place in England.
Glastonbury could close with a temperature of 28C, though this would remain short of the highest temperature recorded at the event of 31.2C in 2017.
Wimbledon could see the hottest temperature ever recorded at the opening of the championships. A forecast of 34C would exceed the 29.3C that was measured at Kew in 2001.
Several factors are contributing to this temperature increase including hot air from the heatwave in the eastern side of the United States and hot humid air from the Azores, plus strong sunshine and building high pressure over England.
The forecast constitutes extreme heat and is not far away from the June record which stands at 35.6C and was recorded at Southampton during the summer of 1976.
Heatwaves are becoming more common due to climate change, with a greater chance of seeing extreme heat.
The Met Office said heatwaves were 30 times more likely to occur than before the industrial revolution - and were projected to become even more common, potentially occurring every other year by the 2050s as greenhouse gas concentrations continue to rise.