High tides and strong winds along the coast could lead to flooding this evening.
At least ten flood warnings in southwest and southeast Wales are expected tonight as well as numerous flood alerts, Environment Agency Wales said.
The agency is urging people to be careful if they are driving or walking in coastal locations this evening as sea spray and overtopping caused by the high waves could cause flooding.
People should avoid exposed areas where there is a risk of being swept away by waves or hit by debris thrown up by waves, the agency warned.
Low-lying coastal roads, farmland and isolated houses could be vulnerable.
Stop logs and flood gates have been installed in Loughor, Newton Foreshore and Crofty, and agency officers will be checking flood defences along the coast while they help emergency services respond to incidents.
High tides are expected at Milford Haven initially at 8.20pm and then along the coast to Newport in the southeast at 9.15pm and Barmouth in north Wales at 10.20pm.
For the latest on flood alerts and warnings go to http://www.environment-agency.gov.uk/flood or call Floodline on 0845 988 1188.