Met Éireann has warned that up to 50mm of rain could fall in some areas before tomorrow morning.
A weather advisory from the forecaster said intense downpours in some areas could also bring localised flooding.
The heavy rain led to the postponement of a GAA fixture in the south of the country. The AIB Leinster senior hurling semi-final between Oulart the Ballagh from Wexford and Ballyhale Shamrocks from Kilkenny did not go ahead due to a waterlogged pitch.
Met Éireann warned the heavy rain would affect the southern counties of Leinster and Munster today and tonight, and into tomorrow morning.
The forecaster also issued a gale warning and a small craft warning. It said tonight would see north to northeasterly gales developing along the coast from Wicklow Head to Roche’s Point, to Loop Head and on the south Irish Sea. These are likely to reach gale force six or higher.
Highest temperatures today will range from only three or four degrees in the northwest and north, to eight or nine degrees in the south and southeast.