Met Éireann has issued a status yellow rainfall warning for three counties.
The warning for Donegal, Galway and Mayo is in place from 10am today until 3pm tomorrow.
Met Éireann says that "spells of persistent rain will give totals of 25 to 35 mm in parts, mainly over high ground."
A rainfall warning was issued yesterday for Donegal, Galway, Leitrim, Mayo and Sligo, but that has been lifted for Leitrim and Sligo - and extended for the other three counties.
The weekend is likely to see plenty of rain in other parts of the country.
The west and north will have spells of persistent and heavy rain on Friday.
The south and east will be drier and warmer tomorrow. Highest temperatures are expected to be between 15 and 22 degrees.
Saturday will see more rain despite a dry start with Met Éireann saying temperatures could reach 17 degrees.
The forecasters says Sunday will start showery "but some heavy bursts likely and bright or sunny spells will break through."
Sunday evening will see scattered showers that "are likely to remain heavy in the north but elsewhere will become mostly dry with good clear spells."