Amber heat warnings have been issued for parts of southern England as a second heatwave in the space of three weeks approaches.

Temperatures are expected to climb to 30C on Friday, remain high over the weekend, and reach 33C on Monday.

In May the UK’s temperature record for that month was broken with highs of 35C.

Amber heat health warnings, which mean there is risk to the wider population not just vulnerable people, have been issued by the UK Health Security Agency for eastern England, London, the south-east and the south-west from Thursday morning until Tuesday evening. Yellow alerts are also in place for the East and West Midlands.

The Met Office said some areas in southern England are likely to see heatwave criteria met by Saturday and more widely on Sunday. Hot weather is deemed a heatwave when a temperature threshold is met three days in a row, which ranges from 25C to 28C across different parts of England.

However, the rest of the UK is expected to experience cooler temperatures with the maximum in Glasgow expected to be eight or nine degrees lower than in London.

The hottest temperatures are expected to be 32C on Friday in East Anglia, 32C in the south and south-east of England on Sunday, with the potential for 33C in the same areas on Monday.

Gregory Wolverson, the Met Office’s deputy chief forecaster, said: “This week’s weather reflects a contrast we often see in summer, with more unsettled conditions passing to the north-west of the UK while heat builds in the south and east.

“As we move towards the weekend, we’ll see conditions become more widely settled and temperatures rise all round,” he said. “Many parts of southern and eastern England are likely to see temperatures high enough to meet heatwave thresholds.”

Wolverson added that despite the hot weather there would probably be cloudy conditions in places and a chance of thunderstorms.

The Met Office reiterated its water safety advice after 16 people died in water during the May heatwave. The weather service issued a reminder that the sea is still cold at this time of year, which can cause cold-water shock at temperatures below 15C.

The Met Office also encouraged people to be aware of the risk of strong currents and hidden obstacles below the water’s surface, to only swim accompanied by others, and float on their backs if they get into trouble.