Ireland is preparing for what could be its worst storm in half a century when the remnants of Hurricane Ophelia make landfall, bringing wind gusts of up to 130 kilometres per hour.

The storm weakened to a category 1 hurricane as it moved north-north-east across the Atlantic, with sustained winds of 145 kilometres per hour.

It is expected to be downgraded to a post-tropical storm before making landfall in southern Ireland on Monday morning (local time).

But UK Met Office forecaster Luke Miall said it could still pack "hurricane force" winds, and warned of potential power cuts, flying debris and disruption to transport and phone signals. Strong winds could also hit Scotland, Wales and England.

Ireland's Met Eireann weather service said the country's southern and western counties could get gusts of up to 130 kilometres per hour, along with heavy rain and storm surges.

The US National Hurricane Centre said the storm could bring between 50 and 75 millimetres of rain in western Ireland and Scotland, with coastal flooding and "large and destructive waves" where it makes landfall.

Emergency officials in Ireland said schools would be closed on Monday in the eight counties expected to see the strongest winds and under a red weather alert — the highest level.