Met Éireann has issued a rainfall warning for the entire country.
The forecaster said persistent and occasionally heavy bands of rain will cross the country beginning on Sunday night through to Tuesday evening.
There is a risk of localised spot flooding with a heightened risk of flash flooding in mountainous regions where rainfall is expected to be highest.
The warning is valid from midnight on Sunday until 7pm on Tuesday.
Met Éireann said unusually high tides combined with strong winds will create an elevated risk of coastal flooding.
In the North, the UK Met Office has issued a rain warning for counties Armagh, Derry, Down, Fermanagh and Tyrone, with flooding and travel disruption possible.