A status yellow high temperature warning will come into effect at midday for the entire country.
Temperatures are expected to hit 30 degrees or possibly higher in some parts, possibly producing new records for August.
The latest heatwave is set to come to an end in the early hours of Sunday.
Met Eireann forecaster Aoife Kealy says we can then expect some thundery downpours.
"We are going to see some heavy showers on Sunday," she added.
"And, as we move through next week it's going to get cooler with temperatures dropping back to normal.
"There will also be some heavy showers."