Officials said State Route 1 was closed north of the Indian River Inlet Bridge in Sussex County on Wednesday afternoon after waves drove water and sand onto the road.
Emergency management officials urged residents of flood-prone coastal areas to relocate to safer areas inland before tides and flooding cut off exit routes.
State transportation officials also were keeping an eye on the Prime Hook wildlife refuge, an area that is home to about 200 year-round residents served by a primary access road that is often cut off by flooding from storms.
The Delaware National Guard was preparing to assist if evacuations were needed.
