Ferry sailings tomorrow from the UK have been cancelled and flights from three London airports were hit by delays after fog shrouded the UK capital this morning.
Irish Ferries is operating as normal until Friday when Swift services from Dublin to Holyhead have been cancelled along with the planned service on the Oscar Wilde at 10.45am. The same ferries operating back to Ireland from Holyhead have also been cancelled.
Passengers are advised that they can be accommodated on the Ulysses cruise ferry services at other times and to check notices.
Stena Line, which operates from Dublin to Holyhead and Rosslare to Fishguard, warned that some of its services may be affected.
"Winter Storm Barbara is set to bring wet and windy conditions to the UK," it said.
"Unfortunately this may cause disruption to some of our scheduled sailings this Friday and Saturday."
Storm Barbara is expected to sweep over the country from the south and west bringing milder temperatures but heavy rains with the gales.
It comes as Met Éireann has issued two weather warnings for Friday, with Storm Barbara set to pass over Ireland this weekend.
Donegal, Galway and Mayo are expected to be the worst affected, with severe gusts of between 100-120km/h and winds of 65-75km/h.
A Status Orange wind warning is in place for high ground there and for coastal regions.
A Status Yellow wind warning is in place for the rest of the country, with gusts of between 90-110 km/h and winds of 50-65 km/h, strongest on exposed coasts.
The warnings are valid from 6am-6pm tomorrow.
The Road Safety Authority urged drivers, cyclists and pedestrians to exercise caution.
Festive flight plans face being thrown into chaos after Heathrow, Gatwick and London City Airport all experienced a raft of hold-ups due to the weather.
A spokesman for Heathrow said some early-morning flights had been been pushed back and there could be knock-on delays throughout the day, but added that there have yet to be any cancellations.
British Airways said on its official Twitter feed that it was aware of fog affecting flights at all three London airports and advised passengers to check their flight status online.
Fog is affecting flights at London Heathrow, Gatwick & City today. Check your flight status here https://t.co/Md01pAPZDw [06:15 22DEC]— British Airways (@British_Airways) December 22, 2016
A statement on BA's website said: "Fog across parts of southern England is affecting some flights to and from London's airports today.
"For safety reasons, Air Traffic Control has to allow greater space between landing aircraft in fog or during periods of low visibility, and this will mean a reduced number of aircraft being allowed to land each hour.
"We are sorry for the difficulties caused by the poor weather and will do all we can to minimise the effect it has on our operations."
A spokeswoman for Gatwick said "about five or six" flights were diverted to other airports on Wednesday night due to fog and maintenance work on a runway.
She said normal service had resumed by Thursday morning, and they were taking flights diverted from London City.
Scotland is predicted to be the worst hit by the weather, with gusts of up to 90mph forecast in places.
North Wales and the North of England are also due to feel the force of Barbara, which is due to roll in by Friday.
The worst of any destruction is expected between Friday evening and Christmas Eve morning, but the potential for structural damage and disruption to some transport services means the storm's impact could be felt long after the winds have subsided.
Met Office spokesman Grahame Madge said: "We are expecting gusts of around 80mph widespread within the amber warning area, up to 90mph in places.
"We have had the good fortune to be able to issue the weather warnings ahead of Storm Barbara coming, with plenty of time hopefully for people to change their plans if they need to.
"But the nature of the storm means it still has the potential to have an impact on power supplies, structures, and disrupt bridge and ferry crossings."
The UK Coastguard issued its own safety warnings ahead of the weekend.
Coastal operations area commander Ross Greenhill said: "We always advise people to check the weather and tidal conditions before they set out so that they can either prepare accordingly or consider whether they should even be going out at all.
"At sea, changes in tidal streams can make conditions worse, particularly if the wind and tide are against each other and tidal heights may hide underwater hazards."
Storm Barbara has been named in line with the Met Office's alphabetical policy for the strongest weather systems and is only the second name designated this season, which began on October 1, after Storm Angus.
One flight due to arrive at Gatwick at 11.20pm on Wednesday was diverted to Birmingham Airport because of the fog.