An area of deep moisture combined with an upper level trough is expected to generate heavy rains and thunderstorms for the entire state starting on Saturday evening, weather officials said.

The National Weather Service has issued a flash flood watch for Oahu effective 6 p.m. Saturday through 6 p.m. Monday.

Heavy showers are expected to soak the Big Island’s windward side and Maui Saturday night and continue on to the rest of the state on Sunday, weather officials said. Windward areas are expected to have the greatest chance of flooding.