The bad weather conditions could also affect Welsh rugby fans returning home on ferries and planes from Saturday’s Six Nations match in Dublin.
The Met Office has issued a yellow wind warning for the whole of the UK and two yellow rain warnings on Sunday.
Forecasters said winds could reach 80mph (130km/h).
They also warned there could be 3in (80mm) of rain.
The wind warning is in place for the whole of Sunday, while the rain warnings are in force from 00:00 GMT until 21:00.
The rain is set to affect areas on higher ground the most, with 14 counties covered by the warnings.
Organisers of the Llanelli Half Marathon decided to cancel it earlier this week to give the 2,500 competitors warning.
“Our decision has not been taken lightly and whilst it may appear that we have made the call early, the yellow weather warning issued for Carmarthenshire over this coming weekend has reinforced our decision,” said race director David Martin-Jewell.
“With up to gale force nine winds expected, we need to prioritise the safety of all our runners, volunteers, contractors, crew and spectators.”
He added equipment, baggage, barriers, toilets and water stations may not withstand gusts.
It has been postponed until 8 March.
Coastal roads and communities could be affected by spray or large waves due to the strong winds.
These could also bring disruption and delay to road, rail, air and ferry transport.
The counties covered by the rain warnings are Blaenau Gwent, Bridgend, Caerphilly, Cardiff, Conwy, Gwynedd, Merthyr Tydfil, Neath Port Talbot, Newport, Powys, Rhondda Cynon Taf, Swansea, Torfaen and Vale of Glamorgan.