A Status Orange thunderstorm and rain warning has been issued for the entire country.
Met Éireann has said thunderstorms and "very heavy showers" will see significant rainfall accumulations over short time periods.
It said the possible impacts will include flash flooding, difficult travel conditions with reduced visibility and power outages.
The alert, which upgrades an earlier Yellow warning, is in place until 6pm on Tuesday.
Status Orange - #Thunderstorm & Rain warning for Ireland ⚠️ ⛈️
Thunderstorms & very heavy showers producing significant rainfall accumulations over short time periods. 🌧️
Valid: 13:12 20/06/2023 to 18:00 20/06/2023
View all warnings here 👇https://t.co/Xg3aMJlyuS pic.twitter.com/QJ3PhOuLqc
— Met Éireann (@MetEireann) June 20, 2023
A mix of cloud and sunny spells with showers is forecast, with thunderstorms set to develop for the afternoon and evening.
This will bring the possibility of hail and localised flooding, with highest temperatures of 18° to 22°.
Tonight will see heavy showers and thunderstorms easing, becoming mostly confined to northern and Atlantic coastal areas.
Temperatures will not fall below 10° to 14°, with some mist or fog patches developing.
Meanwhile a Yellow thunderstorm warning has been issued for Northern Ireland by the UK Met Office.
The alert - for Antrim, Armagh, Down, Fermanagh, Tyrone and Derry - is forecasting heavy showers and thunderstorms.