The Met Office yellow ‘be aware’ alert for rain is valid in the county between noon today and 6am tomorrow.
A Met Office spokesperson said: “Heavier showers and thunderstorms are likely to break out this afternoon and evening.
“Many parts will miss these, but some torrential downpours are likely in a few places, bringing around 20mm of rain in less than an hour and 30-40mm in a couple of hours.
“Lightning and hail may prove additional hazards in some locations.”