A high temperature warning has taken effect in Longford.
The advisory is also in place in ten other counties and areas of Connacht.
Met Éireann is warning of the possibility of forest fires and heat stress, with maximum temperatures in excess of 27 degrees celsius expected.
While Connacht will come under a thunderstorm warning from 3pm to 10 o'clock tonight.
This will affect counties Leitrim and Roscommon.