Met Éireann's warning people in 15 counties to expect thunderstorms and heavy rain today.
A status yellow alert has been issued for Connacht, Ulster and parts of Leinster and Munster.
It begins at 9 o'clock this morning and will end at the same time tomorrow.
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The UK Met Office has also issued a warning for Northern Ireland.
It says slow-moving, heavy downpours, some of which may be thundery, may cause flooding and travel disruption.
Flooding and dangerous driving conditions are expected across the island.
