At least three guardsmen fainted in the heat during a military parade as temperatures in the UK hit 30C (86F) for the first time this year, while in the Scottish Highlands people were told to stay inside as firefighters tackled a wildfire.
More than 1,400 soldiers were reviewed by the Prince of Wales, who is honorary colonel of the Welsh guards. The event at Horse Guards Parade in central London on Saturday was a rehearsal for trooping the colour. Afterwards, Prince William tweeted that the troops had done “a really good job” in difficult conditions.
The Met Office confirmed temperatures in the UK had reached 30C, with 30.5C recorded at Heathrow.
In the Scottish Highlands, people were warned to stay indoors on Saturday evening as firefighters tackled a wildfire near Inverness on what was the hottest day of the year so far in Scotland. A temperature of 26.7C was recorded in Auchincruive in Ayrshire and 23C in Inverness.
The Scottish fire and rescue service (SFRS) and Police Scotland advised people in the village of Daviot to stay inside and close all windows and doors to prevent inhaling smoke.
The fire started close to a caravan park at about 2.45pm. A “very high” wildfire warning which was in place until Saturday has been extended until Monday, the SFRS said. The fire follows one near Cannich in the Highlands, which began on 28 May and is believed to be one of the largest in the UK, covering about 30 sq miles.
Thunderstorm warnings are in place across much of the country for later on Saturday and Sunday.
Warm air from the south is expected to send the heat rising, but bringing with it thundery showers and the chance of hail and gusty winds, according to the Met Office.
Frank Saunders, a chief meteorologist, said temperatures could reach 31C (87.8F) in parts of central and south-east England on Saturday – along with the chance of torrential rain.
“As the heat builds from the south, thundery showers will develop through Saturday afternoon,” he said. “While not everyone in the warning area will see the heaviest showers, or even any rain at all, some will bring heavy thundery downpours.
“With intense showers there is a risk of surface water flooding, which could cause some disruption.”
A yellow thunderstorm warning – highlighting potential disruption to travel, power cuts and localised flooding – has been issued for Wales and a large part of southern and central England from 2pm to 9pm on Saturday.
A second yellow warning is in place for Wales, Northern Ireland and most of western and central England and Scotland. Parts of eastern and northern Scotland are likely to avoid the most extreme conditions.
Saunders said: “Sunday will see 30C again in parts of the southern UK and the risk of thunderstorms more widely, particularly western and central areas.”
The BBC forecaster Tomasz Schafernaker said the high temperatures would last well into the evenings, but were far from rare at this time of year.
“It is not unusual to get these sort of temperatures in June,” he said. “We’ve regularly approached the low to mid 30s.
“We will notice the humidity rising as we go through the weekend, with some really balmy nights on the way. At 10pm on Saturday, temperatures in some towns and cities will still be hovering around 20C.
“For Sunday there’s a lot of sunshine around, very warm, very humid but with a greater chance of catching showers and thunderstorms across many western parts of the UK … hail, thunder and gusty winds and then it is back to sunshine again.”
The UK Health Security Agency has issued an amber alert for hot weather until 9am on Monday in the West Midlands, east Midlands, east of England and south-east and south-west England.
It means the impact of the heat is “likely to be felt across the whole health service … and the wider population, not just the most vulnerable”.
A further yellow alert, which is less serious and warns there may be some disruption to services due to weather conditions, is in place for the north-east, north-west and Yorkshire and Humber regions of England, as well as London.
The Met Office said thundery showers may continue into Monday and conditions would remain hot and humid with plenty of sunny spells until midweek.