A status yellow high temperature warning will come into effect across the country from lunchtime today, until Friday.
Met Eireann say daytime temperatures will reach as high as 30 degrees, while at night it could be as high as 20 degrees.
The alert will come into effect from 1pm.
Evelyn Cusack from Met Eireann said it will get very hot.
"It'll exceed 29 today and during Wednesday and Thursday it will actually get passed 30 or 31 degrees in parts of the midlands and west."
She said thunderstorms are also a possibilty in some areas.
"Today there is a slight risk of a thunderstorm in the north midlands and west but for much of the day it'll be dry hot and sunny".
She said people should "stay in the shade due to the strong sun and high temperatures."