Winds speeds in parts of England have risen above 50mph as Storm Freya approaches the south west of the UK.
BBC Weather said conditions would deteriorate throughout Sunday with the storm set to bring winds of up to 80mph and dangerous conditions.
The Met Office issued a severe warning for risks of injury and danger to life from flying debris and large waves.
Damage to buildings and trees, travel disruption and power cuts could also be possible.
The warning, from Sunday afternoon to Monday morning, covers parts of Wales, south-west England, the Midlands, northern England and southern Scotland.
Strong winds were seen across Scotland on Saturday night as a separate weather system moved inland.
A gust of around 70mph was recorded at South Uist, while winds of 45 to 50mph blew through Glasgow and Edinburgh.
It follows a week of record-breaking winter heat in the UK.
Met Office spokesman Grahame Madge said winds of 55mph to 65mph were “likely quite widely within the warning area”, with the potential for gusts to reach 70mph and 80mph in coastal areas.
Wind speeds are expected to be highest in Devon, Cornwall, Wales and north-west England.
BBC Weather’s Gemma Plumb said the storm, moving in from the south and west of the UK, was expected to push north across much of the country on Sunday.
She added: “For a time during Sunday evening and overnight there is the risk that some rain could fall as sleet or snow on the hills of southern Scotland and northern England.”
Travellers are advised to plan journeys ahead, as road, rail, air and ferry services may be affected with longer journey times and cancellations possible.
Some roads and bridges may also have to close.
The storm warning comes after a week which saw the UK break its warmest winter day record on two consecutive days, with 21.2C recorded in Kew Gardens, London, on Tuesday.
The Met Office has also provisionally announced that last month was the second sunniest February on record for the whole of the UK.
The forecaster said there were average maximum daily peaks of 10C, beating the previous record of 9.8C set in 1998.
Last February, temperatures in the UK plunged as low as -11.7C at South Farnborough, Hampshire.