The warning covers Wicklow, Cavan, Donegal, Galway, Leitrim, Mayo, Sligo, Clare, Cork, Kerry and Waterford.
Met Éireann says up to 40 millimetres of rain is expected to fall and there will be a risk of localised flooding.
Status Yellow - Rainfall warning for Wicklow, Cavan, Donegal, Galway, Leitrim, Mayo, Sligo, Clare, Cork, Kerry and Waterford.
Valid: 16:00 Tuesday 29/09/2020 to 12:00 Wednesday 30/09/2020.
For more information on weather warnings and advisories:https://t.co/Xg3aMJlyuS pic.twitter.com/fZWvgWiRbj
— Met Éireann (@MetEireann) September 29, 2020
The alert was put in place from 4pm today and will remain until 12pm tomorrow.
The alert had originally been issued for just Wicklow, Galway, Mayo, Clare, Cork, Kerry and Waterford, before the remaining four counties were added earlier today.