Much of the country woke up to a warm and muggy start on the first day of meteorological summer.
A yellow weather warning remains in place until 10pm, covering most parts of the country, including Edinburgh, the Lothians and Fife and Strathclyde.
Scotland is likely to see warm sunshine, scattered thunderstorms and torrential downpours, the Met Office warned.
There is the potential for 20-30 mm of rain to fall in an hour in some locations, with lightning and large hail also possible.
READ MORE: Scotland’s weather: Heavy rain warning for Friday and Saturday
The Met Office said there would be some good spells of sunshine following a cloudy start.
Met Office meteorologist John West said a “lively” day was in store on Friday, despite a bright start for some.
He said: “It will be a warm and humid day, with some decent spells of sunshine. But with the temperatures rising and an awful lot of moisture in the air, we’ll see more heavy showers and thunderstorms returning by early afternoon.
“This will affect Northern Ireland, Scotland and western parts of England and Wales.
“With some torrential downpours, it is likely that we will see some localised flooding.”
The severe weather is expected to ease into the evening, with another humid night in store, but return on Saturday to Scotland and Northern Ireland.
The Environment Agency has urged people to check their flood risk and warned people not to drive through flood water.
Kate Marks, Environment Agency flood duty manager, said teams would work “24/7” to operate flood defences, clear blockages in rivers and streams and support partners at any incidents of surface water flooding.
“With heavy rain forecast during rush hour, drivers should stay up to date with the latest weather forecast and travel information before making their journey,” she said.
“We remind people not to drive through flood water as just 30cm can move your car.”