The National Weather Service in Upton, N.Y., has issued a flash flood warning until 8:30 p.m. for Fairfield, Middlesex, New Haven and New London counties.

Rainfall moving into the Southern Connecticut after 6 p.m. is expected to fall at rates between 1½ and 2½ inches per hour. Doppler radar indicates a few areas that may experience rainfall of 4 inches an hour, which is expected to cause flash flooding of roads, especially in low-lying and poor drainage areas, according to the National Weather Service.

Excessive runoff from the heavy rainfall will cause flooding of small creeks and streams, highways and underpasses. Additionally, country roads and farmlands along the banks of creeks, streams and other low-lying areas are subject to flooding.

Motorists are warned not drive a vehicle into areas where the water covers the roadway. The water depth may be too great to allow the car to cross safely.