Commuters are being warned of travel disruption on Monday as a storm bringing severe gale-force winds starts moving across England and Wales.
Train companies have cancelled early-morning services, and flights into London have been reduced.
Gusts of up to 80mph (130km/h) are predicted as the weather hits the South West then moves north and eastwards and there are fears of flooding and damage.
The prime minister has chaired talks about plans to protect the public.
Meanwhile the search for a missing 14-year-old boy who was swept away by the sea in East Sussex has been stood down.
Robin Gisby, network operations managing director for Network Rail, said commuters should expect considerable disruption.
"This will impact up to Birmingham and up to Nottingham and the Midlands. If we get through this in the morning, restore the service during the afternoon and are able to start up a good service on Tuesday morning, in the circumstances I'll be pretty pleased," he said.
Travel warnings include:
- South West Trains have advised people not to travel on Monday with most services not running until at least 08:00 GMT to allow Network Rail to check lines. A reduced timetable will be in operation, with some trains limited to speeds of 50mph
- East Coast will operate a revised emergency timetable on Monday, with trains stopping at Peterborough until 10:00 GMT, and limited to speeds of 50mph afterwards
- First Great Western and Virgin West Coast main line are also running an amended service until 10:00 GMT and 09:00 GMT respectively
- First Capital Connect and C2C said services are unlikely to begin until 09:00 GMT. Greater Anglia, Southern and Gatwick Express have said services on Monday will not run until it is declared safe to do so
- London Overground will not run a service on Monday before 09:00 GMT, while First Great Western has warned of extended travelling times and Southeastern said it is likely to start running services late
- Airports including Heathrow and Gatwick are warning of possible disruption to flights, advising passengers to check with airlines
- Airlines operating in and out of Heathrow have been instructed to reduce their schedules by between 5% and 20% between the hours of 06:00 GMT and 22:30 GMT, leading to about 60 flight cancellations. It is not yet clear how many of those will be short-haul or long-haul flights
- EasyJet has warned passengers there could be disruption to flights on Monday. It said no trains would run to Gatwick, Southend, Stansted or Luton airports before 09:00 GMT
- Eurostar said it will not be running trains on Monday until 07:00 GMT, with early services from London and Brussels subject to delays. It expects to run a full service after 07:00 GMT and passengers are advised to arrive at the scheduled time
- Several ferry companies have also cancelled services, including some English Channel and Irish Sea crossings
- Several bridges including the M48 Severn Crossing, the A249 Sheppey Crossing in Kent, and the Tamar Bridge which joins Cornwall and Devon are closed. There also are plans to shut the M4 Severn bridge and the Queen Elizabeth II bridge on the M25 on Monday morning, with traffic directed through the tunnel part of the crossing
- The Highways Agency is advising motorists to check the weather forecast and road conditions before they travel
In a conference call, joined by staff from organisations including the Met Office and the environment and highways agencies, David Cameron heard the storm could have a "widespread impact", his spokesman said.
But he was told there were plans in place to minimise the effect on public services such as schools, the NHS, transport and power supplies.
In other developments:
- The Environment Agency has issued eight flood warnings - all in south west England - and 144 flood alerts across England and Wales
- East Sussex County Council says refuse collections have been suspended on Monday because of the safety risk posed by the winds
The Met Office said the predicted storm - named St Jude after the patron saint of depression and lost causes, whose feast day is on Monday - was not one "you would see every year".
It said 20-40mm (0.80-1.6 ins) of rain might fall within six to nine hours in the wettest areas.
It has issued an amber alert for high winds in Wales, the East and West Midlands, the South West, London and the South East and the East of England.
A yellow alert warning of heavy rain that could lead to surface water flooding and disruption is in place across much of northern Wales and northern England.
An amber warning means "be prepared", while yellow means "be aware". No warnings are currently in place at the top red level, which means "take action".
Forecasters said exposed coasts in Cornwall, Devon, Dorset, Hampshire, West Sussex, East Sussex and Kent could face the strongest winds.
The Environment Agency has warned of the possibility of surface water flooding on Monday, assessing a number of areas as "medium" and "low" risk.
BBC Weather presenter Jay Wynne said gusts along the south coast were already in the region of 50-60mph and there was some heavy rain spreading up through the south west and southern counties of England and the south of Wales.
The strongest winds are expected in the early hours of Monday as the storm tracks its way across the southern part of the UK but should have moved across the country to the North Sea by lunchtime.
The Metropolitan Police is urging people to use its 101 number during the storm rather than 999, unless there is a "genuine" emergency
Kelly Oster-Coyle, of the Association of British Insurers, said people should do "small practical things" to prepare for the storm but insurers knows "things will be flying around" in the high winds and will be ready to pay out to customers.
Wind speeds of 115 mph were recorded during the so-called Great Storm of October 1987.
There is more information about the forecasts for Sunday and Monday on the BBC Weather, Met Office and Environment Agency websites. See BBC Travel News for up to date travel information and the Highways Agency and Traffic Wales websites for details about road conditions. BBC Local has information from your area.