A status yellow rain warning has been issued for six counties by Met Éireann.
Since midnight, counties Carlow, Cork, Kilkenny, Waterford, Wexford and Wicklow have been subject to the weather warning, which will remain in place until midday today.
Downpours may cause localised flooding, poor visibility and difficult travelling conditions, the forecaster has said.
Overnight there were outbreaks of rain in Munster and south Leinster, which turned heavy in places.
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In other parts of the country it remained mostly dry and clear, with temperatures dropping to between 10 and 14 degrees.
Rain will spread northwards across the country this morning and afternoon, while it will clear northeastwards and turn to scattered showers in the evening.
Today highest temperatures will reach 16 degrees in some places, with winds easing later.
Tonight will stay clear but there may be some showers, turning cloudier overnight with drizzle and moving from the south, according to Met Éireann.
Temperatures will dip to between 8 and 12 degrees, while it will be milder in the southeast.
Unsettled conditions are expected to continue for the rest of the week, with wet and blustery weather. However, it will continue to be mild.
There is uncertainty in the forecast for the weekend, but current guidance suggests a dry and bright day on Saturday, once any mist and fog clears, followed by a more unsettled day on Sunday.
