Met Éireann has issued two Status Yellow rainfall warnings for today and tonight.
The first warning covers Waterford and Cork, with possible rainfall of up to 40 millimetres.
The second warning is valid for Leinster from 6pm this evening.
Met Éireann said it will be mostly cloudy today with showery outbreaks of rain extending northwards to affect much of the country and that the best of dry weather would be across north and east Ulster.
Highest temperatures are between 14 to 18 degrees.
Met Éireann's Matthew Martin said: "The initial warning affecting Waterford and Cork is in operation until 6pm. We're already receiving reports of up to 20 millimetres of rain there so far, and there will be further continuous rain through the rest of the afternoon.
"That will expire at 6pm as the frontal ban moves for the North and then the focus will be on the risk of some thundery downpours affecting Leinster through the overnight period through the night and into tomorrow."
