Met Éireann has issued three separate status yellow weather warnings for rain.
One rainfall warning is in place for Carlow, Kilkenny, Wexford and Wicklow - with between 25 to 40 mm of rain expected.
It warns higher amounts are likely in the Wicklow Mountains.
This alert is in place from 6.00pm on Friday until 6.00pm on Saturday.
Another warning for Galway, Mayo, Clare, Limerick, Tipperary and Waterford is also predicting up to 40 mm of rain in the 24-hour period.
The forecaster also says higher amounts are possible on some mountains here.
This warning is in effect until midday on Saturday.
A third yellow alert is in place for Cork and Kerry.
Met Éireann says between 30 to 50 mm of rainfall are expected here.
It says this will be heaviest between noon and midnight on Friday.
It also says there is a risk of flooding, with highest risk in south and west Cork - as well as south and west Kerry.
The third warning has been issued until 11:00am on Saturday.
— Met Éireann (@MetEireann) January 12, 2018
The Road Safety Authority (RSA) is asking road users to exercise caution while using the roads on Friday night and for much of Saturday.
It is asking people to check national and local weather updates over the weekend, and to also check local road and traffic conditions before making a trip.