Coastal flooding dogged southern Maine for a third day Sunday as astronomically high tides and the remnants of a powerful nor’easter that knocked out power to more than 1.8 million homes and businesses to the south of Maine continued to batter the region.

Powerful ocean swells tore through rock sea walls and washed away dunes in coastal York County, prompting the National Weather Service on Sunday to issue a coastal flood warning for York County and a flood advisory for Portland to Penobscot Bay that was to remain in effect through 3 a.m. Monday.

John Cannon, a meteorologist with the National Weather Service in Gray, said those swells not only knocked out shoreline protective barriers, but dumped sand, rocks, seaweed and debris on shoreline roads, making them impassable.

“There was a lot of dune and structural damage in York County, which means those coastal areas have lost their protective armor, and we have another potentially significant coastal storm coming in midweek,” Cannon said Sunday evening.

That midweek nor’easter, according to Cannon, will affect the entire state, bringing with it a potentially significant amount of snowfall, starting Wednesday evening and lasting into Thursday.

“The snow will be plowable,” Cannon said, but added it is far too early in the week to forecast accumulation totals.

However, News Center Maine in its Sunday evening forecast predicted the nor’easter could drop 6 inches and possibly up to a foot over the state.

But for now, the southernmost regions of Maine continued to cope with the fallout from the storm that started Friday and battered the region between North Carolina and Maine. The next astronomical high tide in Portland was set to begin around 1 a.m. Monday, and Cannon said those powerful ocean swells could continue into Monday and possibly Tuesday.

News Center Maine on its website posted a video that showed gigantic ocean waves surging underneath the pier at Old Orchard Beach. The waves swept over the public beach and carried water onto the concrete surface at the Palace Playground amusement park.

Kennebunk police on the department’s Facebook page Sunday warned motorists to avoid Beach Avenue, which remained closed from Bayberry Avenue to Narragansett Point until further notice.

The town of Wells also got more flooding at Sunday’s 12:45 p.m. high tide, but two hours later crews were beginning to reopen roads shut down by the high water. Wells police announced on Facebook that while most ocean access roads were open Sunday night, drivers might encounter barricades in some spots that public safety officials felt were unsafe.

In York, Long Beach and Ocean avenues and Shore Road were closed during the high tide but only a portion of Shore Road remained partially closed as the tide ebbed.

Saco Fire Department Capt. Bill Madore said Camp Ellis suffered severe damage from the storm. The oceanside foundation of one home at the intersection of Surf Street and Fairhaven Avenue became detached from the home after being battered by waves.

“The house is hanging out over the Atlantic Ocean,” Madore said. He is not sure if the home can be shored up and saved. It was unoccupied during the weekend storm.

Madore said the storm flooded basements and destroyed what remained of Surf Street.

“Surf Street doesn’t exist anymore,” Madore said. “But then again we have been losing parts of Surf Street for 20 years. It’s all broken up.”

Madore said he expects the flooding to continue to subside after Sunday.

“There will be far less. The winds have died down, so we are not getting the storm surge into the bay,” he said.

An excavator, operated by a Saco Public Works employee, tries to clear sand from a flooded North Avenue in Camp Ellis in Saco on Sunday. (Gregory Rec/Portland Press Herald)