Met Éireann has issued a status orange rainfall warning for Munster, Leinster, Connacht and parts of Ulster.
The weather service says widespread heavy rain may lead to flooding.
There's also a five to 15% chance tornadoes could develop.
An orange alert is the second highest level of weather warning.
Explaining the alert, the Met Office said it issues them in order to protect the lives and livelihoods of all of the nation’s citizens, and to mitigate damage to property and disturbance to economic activity.
An orange alert means you should 'be prepared'. It's designed for conditions which have the capacity to impact significantly on people in the affected areas. The issuing of an orange level weather warning implies that all recipients in the affected areas should prepare themselves in an appropriate way for the anticipated conditions.