Met Éireann has issued a status yellow rain warning for 16 counties today.
The alert for counties in Connacht and Cavan comes into effect from 2pm on Friday and remains in place until 9am on Saturday.
Another status yellow warning will come into effect from 6pm on Friday evening for counties Dublin, Kildare, Laois, Longford, Louth, Meath, Offaly, Westmeath, Wicklow and Monaghan. The second alert remain in place until 1pm on Saturday.
A wind warning for Cork, Kerry and Waterford will comes into effect overnight on Friday and stays in place until 12 noon on Saturday.
Forecaster with Met Éireann, Liz Walsh, says conditions will turn very wet on Friday afternoon and evening, with Sunday set to the best day for outdoor activities this bank holiday weekend.
"Cloud will gradually thicken from the Atlantic, with outbreaks of rain developing the west and southwest on Friday afternoon, extending eastwards through the evening.
"There'll be some heavy downpours later in the west, with spot flooding likely there.
"Probably Sunday is looking like the best day for outdoor activities if you're managed to dodge the showers.
"Saturday afternoon and evening are not looking too bad either, but from Friday afternoon through to Saturday morning, a low pressure system will bring a spell of wet and windy weather.
"Then we're looking at another spell of rain coming through on Bank Holiday Monday."