The UK Health Security Agency (UKHSA) has put yellow heat health alerts in place for the East Midlands, east of England, London, South East, South West, and the West Midlands.
They will last from 9am on Friday until 9am on Sunday – with millions of drivers expected to make summer getaways in the coming days.
The AA estimates that approximately 6.3 million drivers are planning a road trip of more than 100 miles between Friday and Thursday.
Temperatures in the affected areas could reach the mid-to-high 20s, potentially climbing up to 30C in parts of the South East.
Meanwhile, parts of Northern Ireland and Scotland will see patches of cloud, with outbreaks of rain set to spread into northern England and parts of Wales on Saturday.
Met Office forecaster Craig Snell said that temperatures will turn “fresher” across much of the UK on Sunday, with rain possible in “areas that haven’t seen much” over the past few weeks.
It follows extended periods of hot and dry weather, with July on track to become the driest in Wales for almost 190 years.
England, meanwhile, has recorded just 3% of its average July rainfall, with hosepipe bans currently in place for 23 million people.
The Environment Agency today confirmed that several areas have been moved from the category “normal” to “prolonged dry weather”.
This includes all of southern England, excluding all of Kent except the north-west of the county. East Anglia, Lincolnshire, Northamptonshire and the West Midlands are also experiencing prolonged dry weather.
Reservoir storage in England is currently 75%, 7% below the long-term average for the time of year.
Wildfires have taken hold in various parts of the country, and Scotland was hit by a major wildfire in the Cairngorms.
The Republic of Ireland also declared a nationwide hosepipe ban in response to the conditions.
It comes after droughts were declared in two areas of Wales.
North Wales and the Upper Severn became the first parts of the UK to declare drought status with the announcement from Natural Resources Wales on Thursday.
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The areas affected included North Gwynedd, Ynys Mon, South Gwynedd, Dee (Wales), Clwyd, and the Upper Severn, which covers mid-Wales.
The third heatwave of this year saw ponds and wetlands dry out, which will impact bird breeding, and other rivers have dried up in places.
The UKHSA alert is in place to offer early warning to the health and social care sector along with government departments when adverse temperatures could impact the country.
