Met Eireann has issued three Status Yellow Rainfall warnings for 12 counties.
They predict between 25mm and 40mm of rain from noon today to noon tomorrow for Clare, Galway, Limerick, Mayo, Tipperary and Waterford.
They say that flooding is possible in these counties and also in counties Carlow, Kilkenny, Wexford and Wicklow where the rainfall warning extends from noon today until 6pm on Saturday evening.
Higher rainfall is possible in mountainous areas and likely in the Wicklow Mountains.
In Cork and Kerry, they have forecast between 30mm and 50mm of rain up to 11am tomorrow morning.
Heavy rain in the W & SW will gradually extend over Munster, Connacht and west Ulster. Spot flooding is likely, especially in parts of Kerry & Cork. Mainly dry in Leinster and much of Ulster. Max temps of 6 to 9°C with freshening S to SE winds.
Rain extending to all areas tonight pic.twitter.com/QAshOaB4UE— Met Éireann (@MetEireann) January 12, 2018
They have also predicted some flooding in the area up until midnight tonight, especially in south and west Cork as well as south and west Kerry.
Road users are being advised to slow down and watch out for potential flooding this evening.
The RSA's Brian Farrell says people need to be wary of potential hazards.
He said: "When Met Eireann start forecasting rainfall of up 50mm, we really do need to take heed of that warning.
"The key thing is to slow down. In wet weather conditions and flooded road conditions, you're going to take longer to stop your vehicle, so slow down and leave extra space between yourself and the vehicle in front."
- Digital desk