As much as two inches of rain had fallen in the city as of Friday morning, and the rain was expected to continue throughout the day, Accuweather.com reported.
A flash flood warning was issued for Oklahoma City. Commuters were advised to not drive their cars through flooded roadways.
Strong thunderstorms were also predicted for Chicago and other parts of the Midwest, Accuweather said. Rain began falling in the early afternoon.
Storms were expected to intensify and continue into the evening, accompanied by 50 mph winds and hail, Accuweather said.
Coastal areas in California's Los Angeles and Orange counties saw a thunder and lightning storm early Friday that moved onto land, bring heavy rains, the Los Angeles Times reported. The rain there was expected to continue through Friday.
Meanwhile, Tropical Storm Dorian, which moved off the coast of Africa last weekend, is moving over the Atlantic Ocean and may hit the Leeward Islands in the Caribbean late next week, Accuweather reported.
The islands may experience strong winds and downpours on Sunday and Monday as the storm approaches, Accuweather said.