(CNN) Communities in the Washington, DC, metro area are still at risk for coastal flooding Sunday as forecasters say about 12 million people remain under flood warnings and advisories.
Coastal areas in Washington, Maryland and Virginia have been experiencing heavy flooding since Friday, and some flooding may occur through Sunday evening, forecasters said.
Tidal flooding is expected to hit shorelines in Washington and Northern Virginia with 1 to 2 feet of inundation in low lying areas, the National Weather Service (NWS) said in its coastal flood advisory that's in effect until 6 pm Sunday.
In Southwest DC, the Municipal Fish Market at the Wharf could flood again Sunday. The market, which sits along a waterfront, saw flooding so high on Friday that some customers couldn't reach some of the shops there.
And in historic Old Town Alexandria, water is expected to approach buildings near King Street and Union Street.
"Shoreline inundation up to one foot above ground is possible elsewhere," the NWS warned.
The weekend weather system was expected to bring some of the worst tidal flooding the region has seen in the past 10 to 20 years. Water levels in parts of the region reached knee-deep for some residents Friday.
The high tides on Sunday will present the greatest threat for water to move farther inland.
The Washington Channel -- which runs parallel to the Potomac River in Washington -- could see a high tide that will bring water levels up 2.5 feet above normal around 5:09 pm. Alexandria's high tide is expected at 5:27 pm, bringing the same level of water.
Alexandria city officials urged residents to take precautions.
"Property owners are urged to take the necessary actions to protect flood-prone property; if you must travel, then do not drive around barricades or through water of unknown depth," the city warned on its website.
Coastal Marylanders also saw significant flooding over the weekend -- particularly those in Anne Arundel and Baltimore counties.
In Annapolis, water crept up businesses' doorsteps, forcing them to close, CNN affiliate WJZ reported.
And small businesses in Anne Arundel County that were shut down or suffered damages due to the flooding could qualify for a grant up to $50,000, WJZ reported.
"As a small business owner, I know how hard it can be to recover from property damage and business interruptions caused by events like this storm," County Executive Steuart Pittman said Saturday, according to WJZ.
And to help Maryland residents with questions regarding flood damages and insurance, the Maryland Insurance Administration will open Virtual Disaster Center Sunday. Residents have the option to ask general insurance questions or meet privately with a representative.
Gov. Larry Hogan declared a state of emergency Friday for areas along the shores of the Chesapeake Bay, the Potomac River and the Atlantic Coast.