The Met Office has warned of “potential danger to life” as the remnants of Hurricane Ophelia head for the British Isles with 80mph (130km/h) winds.
An amber warning for Northern Ireland, west Wales, south west Scotland and the Isle of Man is in force from midday.
In the Republic of Ireland, Met Eireann has issued a red wind warning and the government has deployed the army.
The BBC’s Ireland correspondent, Chris Page, said it would be the most severe storm to hit Ireland in half a century.
Met Eireann has recorded gusts of 92mph (148km/h) at Fastnet Rock, off the south coast of Ireland.
Ophelia is on its way from the Azores in the Atlantic Ocean and it comes 30 years after the UK’s Great Storm of 1987.
The Met Office said there was a “good chance” Northern Ireland could be hit on Monday afternoon by power cuts, flying debris, large waves in coastal areas and disruption to all travel services.
A yellow warning of “very windy weather” also covers parts of Scotland, the west and north of England and Wales.
Met Eireann meteorologist Joanna Donnelly told BBC Breakfast that “hurricane-force winds” were expected and the “real impact” for the Republic of Ireland will be about midday.