Met Eireann have issued a Status Yellow weather warning for half the country, with up to 40mm of rain to lash the east and south.
The national forecaster's rainfall warning covers all of Munster and Leinster and will come into effect at 7pm tonight lasting until 7am on Friday.
A forecaster said: "Heavy rain will spread from the south Thursday evening and night.
"Accumulations of 25mm to 40mm will occur over a relatively short time period. Spot flooding is likely."
However, we will see some sunshine before the rain sets in with highs of 18C to 22C today.
Met Eireann said: "Any early mist or fog patches will clear and much of today will be mainly dry with bright or sunny spells.
"Towards evening heavy rain will develop in the south and will spread northwards over the southern half of the country by nightfall.
"Highest temperatures of 18C to 22C with light easterly breezes, which will freshen in the south later."
Over the course of tonight, the rain will move northwards, reaching the north coast after midnight.
Clear spells and showers will follow in the south.
Looking ahead to Friday, the north of the country will see some heavy rain will continue for a time, but it will clear northwards.
But more heavy showers will follow from the south, becoming widespread and continue through the day. Some of the showers will be heavy with a risk of thunder.
Highest temperatures will reach 17C to 20C with moderate southerly breezes.
Meanwhile, the weekend looks set to be showery and slightly cooler on Sunday.
