The National Weather Service has issued a flash-flood warning for the Ann Arbor area until 5:30 p.m. Sunday and a severe thunderstorm watch until 9 p.m.

The warning area includes all of Washtenaw County as well as Wayne County and parts of Oakland and Macomb counties. The weather service said 1 to 2 inches of rain had already fallen in parts of the area and up to 2 more inches could fall in the next one to three hours.

The weather service advised motorists not to try to drive through flooded areas on roads or freeways and said most flood deaths occur in vehicles.

The weather service had earlier issued a flood advisory for Washtenaw County saying excessive runoff from heavy rainfall would cause ponding of water in urban areas, on highways and streets and underpasses, as well as in poorly drained an low-lying spots.

Forecasters warn showers and thunderstorms this afternoon could produce torrential rainfall that, in addition to causing flooding, could greatly reduce visibility.