Met Éireann has issued a fresh warning for high temperatures for 20 counties in the midlands, south and west.
It comes into effect at 12 noon on Wednesday and runs until 6am on Friday.
Temperatures above 27 degrees are forecast in counties Carlow, Kildare, Kilkenny, Laois, Longford, Offaly, Westmeath, Cavan, and Donegal, as well as Munster and Connacht.
Met Éireann is also warning of uncomfortable sleeping conditions as nighttime temperatures aren't expected to fall below 15 degrees.
Meteorologist Cathal Nolan, from Ireland's Weather Channel said the next few nights could be a challenge.
"Wednesday night, Thursday night and Friday night, they're likely to be quite troublesome for a lot of people across the country.
"Temperatures on those nights in many places will struggle to get below 17, 18, or 19 degrees in some places.
"Irish homes are very good at keeping in the heat, but not very good at dispersing it out."
A high temperature warning, for high temperatures on the west coast, has also been extended to include Co Clare.
The Status Yellow high temperature alert remains in place until 7am on Wednesday morning for Cork, Kerry, Limerick, Galway, and Mayo.
Met Éireann is also warning of an increased risk of heat stress, forest fires and drought, as well as potential water safety issues due to more people swimming in lakes, beaches and other waterways.
