The Met Office's warning of very strong winds has prompted a safety warning from the RNLI.
Gusts of up to 70mph could hit parts of south Wales.
The RNLI says if you find yourself in the water unexpectedly, relax and float on your back to catch your breath and try to grab hold of something to keep you afloat.
The initial shock of being in cold water can make you gasp and panic but, it says, these effects pass in less than a minute, so don’t try to swim straight away.
Keep calm and catch your breath, then call for help, or swim for safety if you can.
If you see someone else in danger in the water, call 999 and ask for the Coastguard. If you have something that floats or that they can hold on to, throw it to them. Don’t go in the water yourself – too many people drown trying to save others.
The water can be unpredictable at the best of times, but it is particularly dangerous during bad weather. We are urging everyone to respect the water and to keep safe during the upcoming rough weather and would remind people not to underestimate the distance waves can travel up the beach or harbour wall.
More information is available here.