A 16-year-old boy has become the latest person to die after swimming in open water as England’s heatwave is set to be replaced by torrential thunderstorms.

Warnings about the dangers of open water have been issued by charities this week as temperatures soared, but a yellow warning of rain is in place for parts of England over the weekend.

A Cheshire Police spokeswoman said the teenager was reported missing at about 2.30pm on Thursday after swimming in the River Dee in Chester and, after extensive searches, a body was found shortly before 8pm.

Superintendent Myra Ball said: “Sadly, this is the second river death that we have seen this week in the county.

“This appears to be another tragic accident and our thoughts are with the boy’s family at this very difficult time.”

On Thursday, the Royal Life Saving Society UK (RLSS UK) said it was aware of 17 incidents of accidental loss of life in the water between July 17 and July 20, and urged swimmers to take care.

All of the incidents had occurred in England, apart from one in Northern Ireland.

RLSS UK charity director Lee Heard said: “Whilst we recognise how tempting it is to cool off in the UK’s beautiful waterways, they hide hazards that tragically take lives each year and we urge the public to use caution when entering the water, getting acclimatised to the water temperature before jumping in.

“The difference between the air temperature and water temperature can literally take your breath away; this is called cold water shock. It is silent, invisible and deadly.”

A Met Office amber warning for extreme heat had been in place for England until midnight on Thursday.

The country reached its hottest temperature of the year on Tuesday when 32.2C was recorded at Heathrow Airport in west London, while on Thursday a 31.1C high was recorded in Ross-on-Wye, Herefordshire.

But forecasters warned that more unsettled weather is on the way, with a yellow warning for rain issued for central and southern parts of England and Wales from early on Saturday to midnight on Sunday.

The Met Office predicted heavy and thundery showers would break out over the course of the weekend, especially on Sunday, which could be widespread and torrential in places.

It warned of potential flooding, poor travel conditions, lightning and hail.

Met Office Deputy chief operational meteorologist David Oliver said: “This yellow rain warning comes as temperatures are set to dip for many areas over the weekend.

“A spell of rain, heavy in places perhaps with some thunder, moves in from the South West late on Friday and into Saturday.”

Wales recorded its highest temperature of the year so far on Thursday with 31.2C in Gogerddan – and it will remain hot on Friday with the mercury climbing as high as 29C.

Scotland also recorded its highest temperature of the year so far with 29.3C in Threave.

Meanwhile, the scorching 31.4C experienced in Armagh at 3.20pm on Thursday is Northern Ireland’s highest temperature on record – with the chance of the figure being broken yet again on Friday.