A flash flood warning is in effect for western Baltimore County and northern Baltimore City.
The warning, issued at 4:42 p.m. by the National Weather Service, is in effect through 7:45 p.m.
Pikesville is among the areas that could be affected by an additional inch of rain, the warning states.
Other communities that could be affected by heavy rain include Timonium, Cockeysville and Towson. Specific areas could also see the heavy rain: Druid Hills Park, Fallstaff, Guilford, Homeland, Howard Park, Morgan State University, Roland Park and Woodring.
The NWS warns residents and travelers to avoid driving vehciles into areas where water covers the road.
"Floodwater is usually deeper than it appears," the warning states. "Just one foot of flowing water is poerful enough to sweep vehicles off the road. Make the smart choice when flooded roads are encountered: Turn around, don't drown."