Met Éireann has issued a Status Yellow rain warning.
The warning was initially issued for counties Cork and Kerry, and is now in place for Waterford too.
It will come into effect at 2:00p.m on Sunday (November 30) and will remain in place until 9:00a.m on Monday.
Met Éireann said persistent rain, heavy at times can be expected.
Possible impacts include localised flooding and difficult travel conditions.
Today (Saturday) brings a mix of cloud and sunny spells with scattered outbreaks of rain and drizzle sinking southeastwards, clearing by early afternoon with sunshine and the odd shower following from the north west.
Scattered showers will develop in the west and north west after dark.
There will be highest temperatures of 6° to 9° in moderate north to north west winds, fresher at times near eastern coasts.
Tonight will be cold and mostly clear with some showers, mainly in the north and west early in the night.
Frost and possibly some ice will form in places with lowest temperatures of -2° to 2° can be expected.
Light westerly or variable breezes with allow mist and fog patches to develop.
It will be predominately dry and bright Sunday morning with just isolated showers.
However, cloud will build from the west with rain following into the west and south west in the early afternoon, extending eastwards to all areas by early evening as southerly winds increase fresh to strong.
Sunday night will see widespread rain at first, which will clear eastwards as fresh to strong southerly winds ease.
Some clear spells and showers will follow into the north and west.
After a brief reprieve in Munster and south Leinster, another spell of rain will push up from the south.