Met Eireann has issued a status orange rainfall warning for Dublin, Louth, Wexford, Wicklow, Meath and Monaghan
It says a spell of heavy rain on Thursday followed by another spell of heavy rain on Thursday night will give rainfall accumulation of 40 to 60 mm with localised flooding.
Met Eireann also issued a status yellow rainfall Warning for Munster and Connacht as well as Carlow, Kildare, Kilkenny, Laois, Longford, Offaly, Westmeath, Cavan and Donegal with heavy rain overnight and on Thursday to give rainfall accumulations of 25-40mm with localised flooding.
Latest forecasts say heavy rain will develop in the west shortly after midnight and will spread across Munster, Connacht and south Leinster overnight with a risk of flooding.
Met Eireann says it will become windy also as southerly winds increasing strong and gusty with gales in some coastal areas. Lowest temperatures of 5 to 7 degrees.
Thursday morning will also be very wet with heavy rain in all areas and a further risk of flooding.
Forcasters say the rain will clear slowly northeastwards through the afternoon and early evening with clear weather and some scattered showers following.