Gale force winds are expected to cause widespread disruption as Storm Brian batters Britain and Ireland less than a week after ex-hurricane Ophelia wreaked havoc.
Winds of 60mph have struck the Welsh coast and gusts are set to reach speeds of 70mph on Saturday.
Forecasters have warned of the potential for power cuts, flooding and delays to transport, as families begin their half-term holidays.
The Met Office has issued a yellow weather warning for winds across a swathe of Britain, including Wales and southern England up to the Midlands, which will remain in place until midnight on Saturday.
Strong winds had already hit southern and south-western parts of Ireland by early Saturday morning.
Met Office forecaster Craig Snell said: “Unfortunately across Ireland it’s the areas that were worst-hit by Ophelia seeing the worst effects of Brian as well.”
People have been advised to stay away from exposed coastal areas and urged not to take so-called “storm selfies” as high tides and a storm surge create dangerous conditions along some coasts.
The Environment Agency has issued 44 flood alerts, as well as six flood warnings urging “immediate action”.
Pictures of Environment Agency staff placing steel flood barriers at Fowey in Cornwall emerged on Friday, as south-western towns braced themselves to become some of the worst-affected areas of the British Isles.
National flood duty manager for the Environment Agency Ben Lukey warned members of the public against posing for photos during the hazardous conditions.
He said: “Environment Agency teams are on the ground, checking defences and taking precautionary action to close tidal gates and put up temporary barriers.
“We’re working with the Met Office and local authorities and are ready to respond as necessary.
“We urge people to stay safe along the coast and warn against putting yourself in unnecessary danger by taking ‘storm selfies’ or driving through flood water – just 30cm is enough to move your car.”
National Rail warned the stormy weather could impact on train services, with emergency speed restrictions imposed on most of the routes in Wales.
A spokesman said: “Fallen trees and other debris may temporarily block railway lines and damage overhead wires.
“Speed restrictions may be imposed in the worst-affected areas for safety reasons, which may delay your journey.”
Drivers were also urged to take extra care on the roads during high winds, as vehicle recovery and insurance firm the AA reminded motorists that surface spray, reduced visibility and potential flooding remained high risks.
The Energy Networks Association, representing the UK’s energy infrastructure, said residents could call the free 105 advice telephone number in case of damage to local network and power supplies.
Storm Brian is the result of a “weather bomb” of low pressure in the Atlantic Ocean.
It follows Storm Aileen, the first UK-named storm of the season, which left thousands of homes without power last month.