Met Éireann has issued an immediate thunder warning for 15 counties on Monday afternoon and evening.
All of Leinster, Cavan, Donegal and Monaghan are affected by the yellow weather warning.
The forecaster is predicting scattered thunderstorms with lightning, hail and a risk of localised flooding in these areas.
The warning is in place from 11am on Monday until 8am on Tuesday.
The UK Met Office has also issued a yellow thunder warning for all counties in the North, from 3pm until midnight on Monday.
It is predicting severe thunderstorms but says there is uncertainty in location and timing.
Looking ahead, Met Éireann says tomorrow will be generally dry and mostly cloudy, with just a few sunny spells and the possibility of some isolated showers.
It will continue to be warm for the rest of the week but is likely to become more unsettled.