Met Eireann has issued a Status Yellow thunderstorm weather warning for and “torrential” rain in Galway and much of the country.
The weather warning states that “thunderstorms will develop today with torrential downpours in some areas bringing a risk of hail and localised flooding.”
It covers all of Munster and Connacht, as well as counties Cavan, Monaghan, Donegal, Kilkenny, Laois, Longford, Offaly and Westmeath.
Only the east coast of the country is not covered by the alert.
The weather warning will be in place until 11pm on Sunday night.
A thunderstorm warning for Northern Ireland has also been issued by Met Eireann, with thunderstorms expected to develop in Armagh, Fermanagh, Tyrone, Derry.
Temperatures today are expected to reach highs of 22 degrees, dropping to 15 degrees overnight.
Poor conditions are forecast to continue into Monday, with overcast skies throughout the day, along with scattered rain, heaviest in the evening.