A rainfall warning has been issued for Windsor-Essex.
Environment Canada says the region could see between 40 to 60 mm of rain.
Speaking on AM800's The Shift, David Phillips, senior climatologist with Environment Canada says what surprised him was how slow moving the rain was.
"It was just inching along. From the radar you could see the rain coming in from just north of Detroit and Michigan, and actually kind of almost just did a turn and then is moving up the 401."
The national weather service says the rain is expected to be heavy at times with the chance of slow-moving thunderstorms.
Phillips says usually storms aren't this slow.
"When it slows down, has more time to spread its misery, then that's when you see the flooding, the pooling, and the ponding and of course in Windsor-Essex County because of the elevation, a lot of flooding can take place."
He says the region has experienced about 10 per cent more rain than usual from April through July.
"Farmers are certainly pleased by the amount of rain, although certainly not too far their colleagues and brotherin to the east have been dealing with just too much rain too often and heavy doses. Haying is very poor in Ontario because of the heavy rains."
Forecasters say heavy downpours can cause flash floods and water pooling on roads with localized flooding in low-lying areas.
The rain is expected to last into the evening hours.
The Essex Region Conservation Authority issued a flood warning for Lakeshore and a watch for the remaining region that is set to expire Saturday at noon.