© Craig Shepheard/Demotix/CorbisFlooding in St Albans last week: the Met Office is predicting that 20-40mm of rain could fall overnight.
Winds of more than 80mph could leave a trail of destruction across large parts of the UK, knocking down trees and causing major structural damage and power cuts.
The storm, named after St Jude - the patron saint of lost causes whose feast day is on Monday - will develop over the Atlantic and is expected to hit the south-west late on Sunday, before moving north-east across England and southern Wales.
David Cameron said he had spoken to the organisations responsible for public safety during the storm. The prime minister wrote on Twitter: "I've just chaired a call with various government departments and agencies to hear about all the plans to ensure people are protected from tonight's storm."
The weather system is expected to have moved out over the North Sea by Monday lunchtime, leaving strong breezes in its wake.
With the Met Office predicting that 20-40mm of rain could fall within six to nine hours overnight, insurance companies are advising households to protect themselves and their property.
Comment: The headline and article from The Guardian sounds a little alarmist. If 20-40 mm of rain within a six to nine hour period is a cause for flooding and major upset, then it is more a sign of a failing infrastructure than of a severe storm.
Or comparison, in Japan the other day 850 mm of rain fell within 24 hours:
Japan's shocking, deadly deluge from Typhoon Wipha: 33 inches of rain in 24 hours
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 Met Office - which has issued an amber warning advising the southern half of England and the southern half of Wales to "be prepared" - described the storm as not one "you would see every year".
It said the expected wind strengths would be similar to storms in March 2008, January 2007 and October 2000.
It has also a lesser yellow warning, meaning "be aware", for the rest of Wales and England up to the border with Scotland.
Frank Saunders, the chief forecaster at the Met Office, said: "We are confident that a severe storm will affect Britain on Sunday night and Monday. We are now looking at refining the details about which areas will see the strongest winds and the heaviest rain."
He advised people to keep an eye on forecasts and warnings, adding: "We'll continue to work closely with authorities and emergency services to ensure they are aware of the expected conditions."
Atlantic storms of this type usually develop further west across the ocean, losing strength by the time they reach the UK and Ireland. The St Jude storm, however, is expected to appear much closer to land, potentially moving across the country while in its most powerful phase, assisted by a strong jet stream and warm air close to the UK.
Chris Burton, a forecaster with MeteoGroup, the weather division of the Press Association, said: "We are going to see some heavy and persistent rain heading north across England and Wales overnight from early this evening, from the south-west.
"As the rain pushes north the winds will pick up, and by midnight there should be gusts of about 60mph across south-west England.
"Through the early hours much of southern England will see winds of 60-80mph, maybe closer to 90mph in exposed areas on the south coast. Further north, in south Wales, the Midlands and East Anglia these will be between 50mph and 70mph."
Burton said the storm should blow across the UK very quickly, with the wind and rain easing off in most areas by Monday lunchtime.
Downing Street said Cameron chaired a call that included transport ministers, the Highways Agency, Met Office, the Environment Agency, the Department for Communities and Local Government and the Cabinet Office.
He received an update from Met Office and Environment Agency about the risk from the storm and associated flooding. No 10 said the prime minister heard that the storm could have a widespread impact, but that transport providers, local government, emergency services and power companies have plans in place to respond.
The Environment Agency said it had teams working to minimise the risk of river floods by clearing debris from streams and unblocking culverts. It is also closely monitoring water levels so that flood warnings can be issued if necessary.
"We are supporting local authorities who will respond to any reports of surface water flooding," said a spokesman.
He also warned people to stay away from seafronts, quaysides and jetties because of the risk of surging waves and wind-blown shingle.
The Highways Agency, meanwhile, urged motorists to watch out for sudden gusts of wind and to give plenty of space to caravans, motorbikes and bicycles.
The AA said drivers should watch their speed, take extra care on dark country roads early on Monday morning and make sure they were wearing warm, waterproof clothes and had a fully charged mobile phone with them.
The forecast has caused the cancellation of ferry services on Sunday and Monday between Plymouth and Roscoff as well as Penzance and the Isles of Scilly.
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."
National Rail warned that the storm would probably affect most routes across central and southern England and Wales. It has issued a list of the train companies that have confirmed either amended timetables or the possibility of amended timetables: c2c; East Coast; First Capital Connect; Greater Anglia & Stansted Express; South West Trains; Southeastern, and Southern & Gatwick Express.
Robin Gisby, Network Rail's managing director of network operations, said: "We are monitoring the forecast closely and have put in place agreed industry plans for dealing with difficult conditions such as these.
"Our maintenance teams will be out over the weekend to check that key drainage points are clear and we will have additional teams available across the network to clear fallen trees and repair any damaged equipment as quickly as possible to allow train operators to keep services running safely. As ever, safety is our top priority."
Heathrow and Gatwick said the weather was likely to cause disruptions and cancellations to their services and told travellers to check the status of their flights with their airlines before setting off for the airport.
The Local Government Association (LGA) said local authorities would divert staff from their normal duties to help out with emergency relief efforts if required.
They have found emergency accommodation should families be evacuated from their homes, and highways teams are on standby to rescue stranded motorists and clean debris from roads.
Councillor Mike Jones, the chairman of the LGA's environment board, said: "Councils are preparing for the worst while hoping for the best. Local authorities up and down the country are preparing to divert staff from their normal duties and have placed additional employees on standby to work with fire crews and other emergency services to get people help if they need it."
Not being in the land of metric always slows down the recognition that this is not much rain. 1mm=.039 inch so 20-40mm=.78-1.56inch in 6-9 hours? Yes, bad infrastructure, planning, zoning or in poor parts of town replace bad with no and it's easy to understand the problem.