There are reports that the downpour has caused a manhole cover to lift in Ravencar Road, Eckington.
Eckington Safer Neighbourhood Team tweeted: "Great Start to the 3 Valleys Festival. Localised flooding may cause disruption.
"Please take extra care on your way."
It said: "Another day with the possibility that thundery weather could cause impacts due to flooding, lightning or possible large hail.
"Many parts will be wet and cloudy but only a few seem likely to see the heaviest downpours."