A severe Status Orange weather warning has come into effect in Waterford and Cork.
"In the 48-hour period from Saturday evening to Monday evening, a spell of heavy rain through Saturday night and Sunday followed by a second spell of heavy rain later on Sunday night and Monday will give large rainfall amounts," Met Eireann warns.
Flooding and hazardous driving conditions are likely in many areas of both counties.
Rainfall amounts will be highest along the south coast and in mountainous areas, making Waterford most vulnerable.
The warning is valid from 6pm on Saturday, April 13 until 6pm on Monday, April 15.
A status yellow warning for similar but less severe conditions is in place for the western half of the country.