Met Éireann has warned that there is a risk of heavy thundery downpours, especially over Munster and Leinster. This may lead to spot flooding.
In Northern Ireland, the Met Office is forecasting that heavy rain and thunderstorms may lead to flooding and disruption to travel.
A status yellow warning is in place from the start of Monday afternoon for the entire island.
It will remain in place until 10pm in the Republic and 11pm in Northern Ireland.
Meanwhile, a status yellow warning is also in place for potato blight.
Warm and humid conditions this week will be conducive for the spread of the parasite, Met Éireann has forecast.
Weekly weather: warm and humid with localised thundery downpours