A status yellow rainfall warning has been issued for five counties.
The warning is in place for Kilkenny, Wexford, Cork, Tipperary and Waterford.
Met Éireann said: "From early hours of Wednesday to noon on Thursday, spells of heavy rain at times will give amounts of 30 to 50mm with a risk of spot flooding."
The warning comes into effect a 12.01am on Wednesday and will remain in place until midday on Thursday.
Tonight will see temperatures fall to between 0 and 3 degrees with heavy showers beginning to develop.
Met Éireann has forecasted rain for most of the country on Wednesday, with highest temperatures of 9 to 11 degrees.
They said that Thursday would be "mostly cloudy" with "some dry spells".
They added that there will be scattered outbreaks of rain, "some heavy and prolonged across the south and east."
Friday is set to see "good dry spells" but Met Éireann added that "showers or showery rain will occur widely".