Gales and large waves bashed the Co Down coast, leaving a number of roads completely submerged on Sunday afternoon.
Part of the Portaferry Road along the Ards Peninsula is under standing water.
Police are advising motorists who plan to travel along the road to Newtownards and Belfast not to use any car park along the route on Monday due to the risk of flooding from high tides.
"Drivers are also advised to proceed with caution as there may be debris swept onto the road by the sea as well as standing water. This could make driving conditions hazardous," a PSNI spokesman said on Sunday night.
Earlier the main Rostrevor Road was also closed for a period after it was completely submerged, however, the road has since reopened.
A warning for strong winds, coinciding with further tidal surges, is valid from the early hours of Monday, increasing the risk of flooding in parts of Belfast and along coastal areas.
High tides are expected at around 2.30am and 2.45pm in the Belfast area.
"Strong winds will combine with large waves to bring the risk of coastal flooding. Winds will gust to 60mph or so on coasts, and locally to 70mph, but waves will be larger than usually associated with this strength," forecasters say.
"The public should be aware of the dangers of waves crashing onshore and over topping shorelines and seafronts."
With one of the worst tidal surges in recent years, we would urge members of the public to take extra care along our coastline at this time. Please stay away from coastal paths, sea walls and cliff edges.
Steven Carson, Belfast Coastguard
The PSNI has been co-ordinating a multi-agency planning team to respond to the unusual weather conditions.
High-level meetings of those agencies have taken place to put in place protocols and contingency measures to deal with multiple scenarios.
Since Thursday over 40,000 sandbags have been handed out to residents in areas at risk and placed at key flood defence locations.
Police say they are preparing for possible flooding on Monday in a number of areas, including:
- Sydenham, east Belfast
- Corporation Street, Belfast
- Sailortown area, Belfast, which includes Clarendon Dock, Belfast Harbour marina, Dock Street and the area surrounding the Odyssey
- Ards Peninsula
Police commander in charge of the multi-agency response, Assistant Chief Constable Stephen Martin said: "We continue to respond to the changing weather conditions with our partnership agencies and plans are in place to deal with the impact these changing conditions may have on the community.
"There is also a risk of flooding in a number of northern and eastern coastal towns and to parts of South Down."
As a precaution, police have advised a number of underground car parks to close.
"While there is a reduced risk of flooding at Belfast City Centre, as a precaution we have advised a number of underground car parks including Victoria Square to close on Monday.
"We would encourage the public not to use any underground car parks in the area.
"We would urge the public to remain on alert and to be mindful of their own safety in particular to avoid coastal paths, be wary of possibly unstable harbour defences and to drive with extreme caution as many roads continue to be affected by surface water."
Because of the dangers powerful waves and winds pose to the public on the shoreline, the coastguard is also warning to avoid all coastal paths.
Belfast coastguard rescue co-ordination centre manager, Steven Carson, said: "These types of conditions, with choppy seas and large waves, are likely to be with us for a few days yet, so please don't take risks.
"If you do get into difficulty, or spot someone else in trouble, call 999 straight away and ask for the coastguard."
A similar warning is also in place in the Republic of Ireland.
Manager of the Irish Coast Guard, Declan Geoghegan said: "The public should exercise extreme caution and venture out only where necessary, also don't go out alone, and have a method of raising the alarm if necessary."
Anyone who needs to report flooding can call a flooding incident line on 0300 2000 100 or the police non-emergency line on 0845 600 8000. More information is available here.
A number of distribution centres have been opened to hand out sandbags to local communities in the following locations:
- Belfast - Palmerston Road from 10am on Monday
- Newtownards - North Road Council Depot
- Portaferry - Market House Square
- Ballywalter - Ballywalter Presbyterian Church car park
- Castlewellan - Bann Road Recycling Centre
- Downpatrick - Strangford Road Council Depot