A heat-health alert has been issued for parts of England as temperatures are predicted to hit 30C (86F) over the weekend.
The alert is in place from 09:00 BST on Friday 9 June to 09:00 on Monday 12 June in London, the Midlands, eastern and southern England.
People are being asked to check on vulnerable friends and family.
The UK Health Security Agency (UKHSA) says the health and social care sector could be impacted.
This first alert – graded yellow – means this weekend, predicted to be hotter than Ibiza and Madrid, could affect the vulnerable including the over-65s and those with an underlying health condition.
Read more:More than 160 Afghans die in bitterly cold weather
Dr Agostinho Sousa, head of extreme events and health protection at UKHSA, said: “In the coming days we are likely to experience our first sustained period of hot weather of the year so far, so it’s important that everyone ensures they keep hydrated and cool while enjoying the sun.
“Forecasted temperatures this week will primarily impact those over the age of 65 or those with pre-existing health conditions such as respiratory and cardiovascular diseases.
“If you have friends, family or neighbours who you know are more vulnerable to the effects of hot weather, it is important you check in on them.”
The UKHSA also advises people to:
BBC Weather meteorologist Tomasz Schafernaker said some parts of the UK official heatwave threshold might be met in parts of England this weekend.
In order for a heatwave to be declared, temperatures must be above the official heatwave threshold for at least three consecutive days.
He said: “Typically highs will reach the mid to high 20s widely across the country, but there is an outside chance of 30C in England. This is dependent on sunshine.
“The forecasts point to increasing amounts of cloud and the chance of thunderstorms which will have a bearing on the highest temperatures.
“Due to the increasing humidity the nights will also become uncomfortable over the weekend.”
Large parts of the country have seen little rain recently, with some areas in England not experiencing any rain since 11 May.
Last year was the UK’s warmest ever – Coningsby, in Lincolnshire, reached a record 40.3C on 19 July.
The UKHSA expects heatwaves are “likely to occur more often, be more intense and last longer in the years and decades ahead”.
The new colour-coded alert system, launched last week, is run by the UKHSA and the Met Office. It is aimed at reducing illness and deaths among the most vulnerable.
With climate change, heatwaves are likely to be more frequent.
There are two further alerts, not yet issued, representing more of a risk:
Individuals can sign up to receive alerts directly here, and people can specify which region they would like to receive alerts for.
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