A status yellow rainfall warning has been issued for nine counties in the west of the country.
Met Éireann is forecasting heavy rain for all of Connacht, Longford, Donegal, Clare and Kerry.
It says there is a risk of localised flooding throughout tomorrow and into tomorrow night.
The warning will come into effect in the early hours of Wednesday morning and will be in effect until 4am Thursday.
There are 25 to 40mm expected of rain forecast in this period.