The worst storm of the winter, which was forecast to hit Britain early this morning, is expected to have a second powerful blast today.

The Met Office said that there would be a brief lull in the storm, which produced gusts of up to 80mph during the night, before another wave of high winds and heavy rain hit the country later this morning. The severe weather is expected to continue until early tomorrow.

Evacutions were under way last night ahead of the impending storm. More than 170 residents of the Lighthouse Park caravan site in Newport, South Wales, were moved from their properties because of potential flooding and structural damage, while residents of about 12 nearby coastal homes were advised to leave by police.

Householders and shopkeepers in the South West have also been told to expect extreme conditions that could threaten lives and property.

The Environment Agency issued seven severe flood warnings – the highest category of alert – for people living on the north and south coasts of Devon and Cornwall. Residents have been told to prepare for evacuation and plan escape routes to higher ground.

The South Coast and South Wales will bear the full force of the storm. It will hit coastlines hard because the winds are expected to coincide with spring tide at high water in some ports.

The agency also issued 44 lower-risk flood warnings, mostly for these areas. The Met Office has issued severe weather warnings for all of England, Wales, Northern Ireland and southern and central Scotland. Residents were told to expect uprooted trees, power cuts and damage to buildings.

The Met Office said that the winds would not be as bad as the Great Storm of 1987, when gales caused damage estimated at £3 billion in today’s values. “This is probably going to be the worst storm of the winter, but it is different from the 1987 storms, when there were gusts of over 100mph and mean wind speed was 60mph. This time it is gusts of 80mph and mean speed of 45mph,” a spokeswoman said.

“The most important thing is not to watch the waves. We know it’s tempting, but it only takes a few seconds for someone to be washed off their feet. It could coincide with high spring tides in Cornwall, Newport, Weston-super-Mare and towns along the coast, such as Bournemouth.”

Airports and ferry companies say that delays and cancellations are possible. Motoring organisations advised drivers to avoid all but essential journeys. Motorcyclists and drivers of high-sided vehicles would be most at risk, the Highways Agency said.

Trains travelling on the main line between London Paddington and Penzance are likely to be affected by winds and waves at Dawlish.

Householders have been urged to ensure that windows are closed and that rooftiles and loose panels secured. The storm was caused by an area of low pressure over North America, combined with the jet stream over the North Atlantic. There could be hail and snow on ground higher than 1,000ft.

P&O Ferries cancelled its sailings from Portsmouth to Bilbao yesterday and from Bilbao to Portsmouth tomorrow. Sailings between Dover and Calais will be delayed by up to an hour. The Environment Agency gave warning that there was a risk of high waves and flooding in Wales, the South West and southern England.

Paul Leinster, its operations director, said: “There will be a potent cocktail of strong winds, wave action and high tides. Gale force winds will combine with spring high tides to elevate the water levels along the coast by up to 1.5 metres over normal levels.”