Severe gales and snow showers are causing travel disruption, school closures and power cuts as Storm Caroline sweeps across the north of the UK.
Forecasters are warning of a danger to life and "devastating winds", with gusts of up to 90mph possible in northern parts of Scotland. Flights and ferry services have been cancelled while dozens of schools are closed across the north of the country.
Train services in the north and west of Britain have been cancelled and the UK Met Office has warned that flying debris could lead to injuries or cause danger to life.
P&O Ferries tweeted shortly after midday on Thursday that all ferry sailings were running on time.
In Ireland, Met Éireann has issued a status yellow wind warning for counties Donegal, Galway, Leitrim, Mayo, Sligo, Clare and Kerry which will remain in place until 8pm on Thursday.
The Irish forecaster has also issued a status yellow snow and ice warning for the whole country with temperatures dropping from 4pm on Thursday and remaining low until 4pm on Friday.
Scattered snow showers will spread on Thursday evening with counties in the north and northwest most at risk, as well as higher ground elsewhere.
Storm Caroline is expected to generate winds of of 55-65km/h, with gusts of up to 110km/h in Irish coastal areas and on high ground, as it moves towards northern Scotland.
As the storm moves towards Scandinavia, it will pull cold Arctic air down across Ireland, leading to snow showers and a risk of ice.
Scattered snow showers will occur later on Thursday and into Friday. Slight to moderate accumulations of snow are possible with up to 3cm in parts.
There will be icy stretches on roads too. North and northwest counties will be most at risk, as well as higher ground elsewhere. The yellow cold weather warning is in placed between 4pm today and 4pm on Friday,
Thursday night will have scattered rain, hail and snow showers; the snow could also settle, especially in the north and northwest. Temperatures will fall to between minus 2 and plus 2 degrees, with frost and icy patches.
Friday will also be cold, Met Éireann said, with sunshine and scattered rain, hail, sleet and snow showers, and temperatures of 3 to 6 degrees in gusty northwesterly winds.
The showers and winds will die down on Friday evening but there will be widespread frost and icy patches will return as temperatures fall to between minus 2 and plus 3 degrees.
Car users are advised to leave extra time to defrost their vehicle before journeys and to bear in mind that stopping distances are up to 10 times longer in icy conditions.
The previous Atlantic storm, named Brian, hit Ireland in late October, less than a week after what began as Hurricane Ophelia.
The next Atlantic storm will be named Dylan.
Additional reporting from PA