Police have advised residents in part of East Belfast to pack their bags for possible evacuation amid fears of a tidal surge.
High water and heavy rain is predicted for midday tomorrow, Saturday and Sunday across Northern Ireland and officers asked members of the public to avoid coastal paths and to drive with extreme caution.
High risk areas include the densely-packed residential streets of Sydenham and Victoria Park in the east of the capital and around the docks.
Police Service of Northern Ireland (PSNI) Assistant Chief Constable Stephen Martin said: "We are particularly concerned around a number of areas, those areas are Victoria Park in Belfast, the Sydenham area of Belfast and around the docks area of Belfast.
"We are working as much as we can to try and prepare ourselves for potential flooding in those areas so during the course of today we have distributed many thousands of sand bags."
Police are coordinating a major planning operation involving many public services.
The Office of First Minister and Deputy First Minister, Belfast City Council, Northern Ireland Fire and Rescue Service, the Rivers Agency, Belfast HealthTrust, Road Service, Northern Ireland Water, Northern Ireland Electricity, British Telecom and Translink are cooperating.
Mr Martin said: "The combination of heavy rain, strong winds and high tides beginning tomorrow and lasting throughout the weekend has created the potential for flooding in a number of coastal areas across Northern Ireland."
He added: "We would ask residents in Sydenham to consider making preparations for potential flooding in the area. We will be working to provide assistance for those who may be affected.
"In general, over the weekend we would ask all members of the public to stay away from coastal paths and walkways and to drive with extreme caution."
Other areas that could be affected to a lesser extent than Belfast include Larne, Newry, Newtownards and Clough in counties Antrim and Down.