Heavy rain is expected in parts of England and Wales on Saturday and could exceed the total amount recorded in May, with thunderstorm warnings issued across both countries.

The Met Office’s yellow weather warning is due to come into force between 9am and 6pm, with gusty winds and hail also likely, as forecasters said up to 40mm (1.6in) of rain could fall over the course of a few hours.

England had 32.8mm of rain in May, almost half the average for the month, according to Met Office data.

The Met Office chief meteorologist Dan Suri said: “Frequent heavy showers and thunderstorms are expected for much of Saturday, before they fade from the west during the mid-to-late afternoon.

“It’s possible that 10-15mm of rain could fall in less than an hour, while some places could see 30-40mm of rain over several hours from successive showers and thunderstorms.

“Frequent lightning, hail, and strong, gusty winds are also possible. A yellow warning for thunderstorms has been issued and covers parts of central and southern England and Wales.

“While brisk winds ensure that most places in the warning area will be hit by showers, not all places will see thunderstorms. In this case it’s difficult to predict where exactly thunderstorms will hit because they are small and fast-changing.

“One analogy we use to picture the complexity of this forecasting challenge is comparing it to boiling a pan of water and having to guess exactly where and when the bubbles will appear.

“We know some will, but only in certain places, and that is why thunderstorms are so hard to predict.”

Sunday is expected to be a drier day for most, with the chance of showers highest in the north of England and also the east at first.