An amber weather warning has been issued across large parts of England and Wales as a hurricane-strength storm builds over the Atlantic and moves towards Britain.
Meteorologists have warned the fierce winds of up to 80mph and torrential rain - which will first strike the south-west of England - could leave a trail of destruction as the storm sweeps north-east across the country, damaging buildings and bringing down trees and power lines.
Roads may also be hit by flash flooding, bringing rush hour traffic on Monday morning to a halt, and homes could be flooded.
Storm clouds gathering over Brighton earlier Pic: Phil Beaven @beevr001
Prime Minister David Cameron said he had chaired a call with Government departments and agencies to hear about their plans to "ensure people are protected from tonight's storm".
He was updated on preparations and contingency planning for transport, schools. hospitals, councils and power supplies.
Mr Cameron was told that the storm could have "a widespread impact", but that transport providers, local Government, emergency services and power companies had plans in place to respond.
The much-anticipated storm - which the Met Office has said will affect Britain on Sunday night and Monday morning - has been named St Jude after the patron saint of lost causes, whose feast day is tomorrow.
Some have compared its potential to the Great Storm of 1987.
Rough seas at Porthleven, Cornwall
Veteran weatherman Michael Fish famously failed to predict its severity before it flattened trees, knocked out power and left 22 people dead in England and France.
This time he has warned people to "batten down the hatches" and to delay their journey by two or three hours on Monday morning.
He told Sky News' Murnaghan show: "There is certainly a severe storm on the way - and we certainly do need to worry about it.
"If you draw a line from about Aberystwyth to the Humber - everywhere south of there looks like getting affected by strong winds, to the north of that the problem is going to be heavy rain and localised flooding.
"These strong winds aren't going to last all that long, but they are going to be unfortunately getting up around about rush hour time, so the message we're trying to convey at the moment is to delay your journey just by two or three hours in the morning, and then you should be safe."
The storm will intensify very quickly when it reaches the UK
Fire chiefs have urged people to stay indoors if possible, and to take extra care if venturing out.
Insurance companies have advised households to take steps to protect themselves and their property.
People should also establish evacuation plans, place valuable items upstairs to limit flood damage and ensure gutters are clear so water can drain away.
The Environment Agency says 20-40mm of rain could fall within six to nine hours.
It has teams working to minimise river flood risk, clearing debris from streams and unblocking culverts, and are closely monitoring water levels so they are ready to issue flood warnings if necessary.
A spokesman said: "Seafronts, quaysides and jetties should be avoided due to the risk of overtopping by waves and wind-blown shingle."
An amber warning is in place across the southern half of England and Wales
Severe weather alerts are in place, with an amber warning, meaning "be prepared", for the southern half of England and Wales.
A yellow warning, meaning "be aware", has been issued for the rest of Wales and England up to the border with Scotland.
Ferry services between Plymouth and Roscof, as well as Penzance and the Isles of Scilly, have been cancelled.
Brittany Ferries, which runs the Plymouth-Roscoff route, said on its website: "We are in the process of contacting all passengers booked on these sailings. We apologise for the inconvenience the cancellation of these services will cause."
Sky News weather presenter Jo Wheeler said: "The storm is coming through at the worst possible time; from around midnight to midday on Monday.
"So Monday morning's rush hour looks like being chaotic with travel and power interruptions anticipated.
"The public are advised to take the greatest care - and to carry a fully charged mobile if travel is necessary.
It has been compared to the Great Storm of 1987
"Winds gusting at 80mph are quite capable of bringing down trees and power lines and causing structural damage.
"Trees are still full in leaf at this time of year and the ground is quite damp so there is more chance they can be ripped from the ground, and branches ripped from trees."
She said Atlantic storms of this type usually develop further west across the ocean, losing strength by the time they reach the UK and Ireland.
But the storm is expected to intensify near to the mainland before it hits the south-west coast with full force, with a strong jetstream and warm air close to the UK contributing to its development and strength.
Darron Burness, head of the AA's flood rescue team, said: "The timing couldn't really be worse, potentially causing significant travel disruption on Monday morning, which is one of the busiest times on the roads."
The Metropolitan Police has urged people to avoid calling 999 during the storm unless there is a real emergency.