Met Éireann has issued a Status Yellow rain warning for a number of counties including Cork.
Forecasters say between 30mm and 50mm of rain will fall today and tonight.
The warning has been issued for counties along the west coast including Cork, Kerry, Clare, Limerick, all of Connaught and Donegal.
Rain will turn heavy and persistent on Friday and Friday night bringing the risk of localised flooding.
"Rainfall totals of 30-50mm are expected during the period, higher in mountainous areas," Met Éireann said.