There is also an amber warning for wind covering Wales from 01:00 to 21:00 and a yellow rain warning until noon.
The last red warning in Wales came during Storm Eunice in 2022, which left tens of thousands without power.
The red wind warning covers Bridgend, Cardiff, Carmarthenshire, Ceredigion, Conwy, Gwynedd, Anglesey, Monmouthshire, Neath Port Talbot, Newport, Pembrokeshire, Swansea and Vale of Glamorgan.
First Minister Eluned Morgan urged people to take the weather warnings seriously.
“Red means there is a potential danger to life,” she said, advising people to only travel if it was “necessary”.