High temperatures could be accompanied by an intense bout of thundery rainfall across a huge stretch of the UK, new weather maps have suggested. While a plume of hot air from the south has set June off to a mild and sunny start, regions in England, Scotland and Wales could be battered by between 20 and 40mm of rainfall in just a few hours by mid-week. The settled conditions that have marked the start of the week are set to shift on Wednesday evening, before heavy downpours drench particularly western and northern areas on Thursday, according to forecasts from WXCharts.

The wet weather is expected to descend upon a great stretch of the country, from the Scottish Highlands all the way down to Wales and London and Southampton in the southeast – with the capital forecast for up to 5.5mm of rainfall each hour by midday on Thursday. Areas around Belfast in Northern Ireland will also be among the worst hit, with a deluge of around 10mm following each hour by Thursday afternoon, with Stoke-on-Trent, Derby and Blackpool also seeing hourly rainfall of around 5mm.

Despite the disruptive weather, the mercury is set to hover firmly in the seasonal average range, with some southeasterly areas even reaching highs of 24C on Thursday evening.

The Met Office has also warned of a change in weather towards the end of this week, with “warm air from the continent” ushering in thundery showers overnight on Wednesday.

The forecaster said the brunt of the bad weather will be felt on Thursday, making for a “more settled” Friday – but warned that “another band of thunderstorms moves in again from the south-west later [on] Friday, bringing further intense rainfall into the earlier hours of Saturday”.

Deputy Chief Meterologist Mike Silverstone said: “After largely benign weather early in the week, some intense, thundery showers will move in on Wednesday evening. These thunderstorms are being triggered by some warm, humid air that is moving into the UK from the south. The intense rainfall could see 20-40mm accumulating over just a few hours, which could cause some disruption.

“While there are no severe weather warnings issued at the moment, it is possible [that] thunderstorm warnings may be issued this week.”

This evening and tonight:

Generally dry and clear, with mild temperatures in the south and chillier conditions in the north.

Wednesday:

A largely dry and sunny day with high temperatures across the country and the risk of a few showers in western areas.

Outlook for Thursday to Saturday:

Warm and humid on both Thursday and Friday, potentially accompanied by heavy and stormy showers. Fresh downpours also possible on Saturday.