Met Eireann has issued a Status Yellow thunder warning for 19 counties.
The weather service said the forecast for this afternoon is for developing thunderstorms across much of Ireland, with several counties in Northern Ireland also affected.
The warning, valid from midday to 11pm, reads: "Thunderstorms will develop today with torrential downpours in some areas bringing a risk of hail and localised flooding."
All of Munster and Connacht as well as Cavan, Monaghan, Donegal, Kilkenny, Laois, Longford, Offaly and Westmeath are all affected.
In the north, Armagh, Fermanagh, Tyrone and Derry are also affected.
The UK's Met Office warning for those counties reads: "Thunderstorms expected to form over parts of Northern Ireland this afternoon."
That warning is valid from 1pm until 9pm.
