The country is set to be lashed on Saturday night and the downpours will persist in many places right through Sunday.
"It will be a wet 24 hours with rainfall in excess of 25mm in many places," says Met Eireann.
The national forecaster said heavy rain is also on the cards for tomorrow night, although it will be a generally dry and cloudy day.
Friday morning will turn brighter.
Saturday will be a bright, cold day with the highest temperatures reaching 6C-9C. However, during the night heavy rain will start to spread across the country.