Large parts of the UK have been warned to brace themselves for terrible weather conditions today, with gale-force winds and the most serious tidal surge for 30 years threatening to flood the east coast of England.
Commuters could face major delays as winds of up to 90mph batter Scotland and northern and eastern England, forecasters said.
The Environment Agency (EA) warned that huge tidal surges could top flood defences bring "significant coastal flooding".
In some places, sea levels could be as high as those during the the devastating floods of 1953, the EA said, although flood defences since then, including the Thames, Deptford and Hull barriers, should provide better protection than 60 years ago.
Disruption is expected on a number of rail routes in northern England and Scotland, including East Coast trains between York and Edinburgh and Glasgow Central, TransPennine Express trains, CrossCountry, Virgin Train and Northern Rail routes, as well as Grand Central trains between Sunderland and York.
Areas most at risk of flooding include the North Sea coast from Northumberland down to the Thames Estuary and Kent.
The EA has issued a severe flood warning - the highest category, warning of danger to life - to homes and businesses near The Quay in Sandwich, Kent, for high tides between 12.45am and 1pm tomorrow.
The tidal reaches of the River Trent, Nottinghamshire, could also be affected today.
On the west coast, severe gales and large waves combined with high water levels are also expected from Cumbria down to Cheshire.
The Thames Barrier was closed last night to protect London, and other defences have been activated at Colne in Essex and in Hull.
Natural Resources Wales is urging people along the north Wales coast between eastern Anglesey and Liverpool to be prepared for flooding today.
As of this morning there were 59 flood alerts across the UK and 34 more serious flood warnings, in the North West, the South East and Wales.
Dr Paul Leinster, chief executive of the EA, said last night: "Gale force winds and large waves along the east coast of England are forecast during Thursday and Friday, coinciding with high tides and a significant coastal surge.
"Flooding of some coastal communities is expected and some defences could be overtopped by the combined effect of high tides, high winds and a tidal surge.
"Coastal paths and promenades will be highly dangerous as there is an increased risk of people being swept out to sea.
"The Environment Agency is monitoring the situation closely, working alongside partners including the emergency services, Met Office and local authorities. Environment Agency teams are out on the ground checking that flood defences and barriers are in good working order, monitoring sea levels and issuing flood warnings."
The Met Office has issued a wide range of weather warnings, with winds expected to gust to more than 80mph as they swing north-westerly in mid-morning, with gusts of more than 90mph in exposed parts.
Much of Scotland faces "be prepared" warnings for wind and lesser "be alert" warnings for snow, while north west and north east England, Yorkshire and Humber, the Midlands, and the east of England are under "be prepared" warnings.
A major traffic route into Leeds city centre, past Bridgewater Place tower - the tallest building in Yorkshire - is being closed today after predictions that wind speeds in the area could reach 75mph.
Only South Wales the South West and southern parts of England will escape the high winds, which will ease during the afternoon.
Laura Caldwell, a forecaster for MeteoGroup, the weather division of the Press Association, said gusts of 60 and 70mph had already been seen in north-west Scotland and the Western Isles.
" The North Sea coast will see winds of up to 80mph, and across the UK it will be quite windy," she said.
"The stronger winds will be mainly this morning and early afternoon, dropping off towards the evening."
England has been largely spared extreme weather so far this winter, but that is expected to change when northerly winds from the Arctic bring freezing temperatures to large parts of the UK with snow showers affecting Scotland, Northern Ireland, parts of northern England, north Wales and the east coast from today.
Temperatures are set to plummet to as low as minus 4C (25F) tonight in parts of Scotland.
Network Rail has warned customers in Scotland and parts of north and eastern England to expect delays.
Robin Gisby, Network Rail's director of operations, said yesterday: "As we saw with the recent storm which affected the south of England, being prepared and on top of severe weather is key to helping us resume normal levels of services as quickly as possible.
"We will be monitoring conditions on the ground closely throughout the night and into the morning and will have teams in place to react quickly to any damage caused by the weather.
"We will keep as much of the network open as is possible however the potential extreme nature of the conditions and the impact it could have on our infrastructure means that speed restrictions and other measures are necessary in the interests of the safety of passengers and our staff.
"We are working closely with the train operators and other industry partners to do everything we can to reduce disruption, while also operating a safe network for passengers."