Met Éireann has issued a status yellow rainfall warning for Donegal, Leitrim, Mayo and Sligo on Sunday.
The forecaster said heavy and intense rainfall with totals of 25mm to 40mm are expected.
It said river levels would be elevated as a result of the rainfall, which may result in some rivers flooding, as well as surface flooding.
The warning comes into effect at 7am on Sunday and will remain in place until 9pm.
Status Yellow - Rainfall warning for Donegal, Leitrim, Mayo and Sligo. Valid: from 07:00 Sunday 04/10/2020 to 21:00 Sunday 04/10/2020. Keep updated on weather warnings here. https://t.co/JAa97a0t2o pic.twitter.com/DGkVVIVIXw— Met Éireann (@MetEireann) October 2, 2020