It will run until Saturday morning with Met Éireann warning of daytime highs of 27 and overnight temperatures no lower than 15 degrees.
The forecaster is warning of the possibility of heat stress, as well as difficulty sleeping at night.
Alan O'Reilly from Carlow Weather says temperatures will get close to breaking records:
"Especially on Friday with lighter winds and very warm air over us, whether we get the all time September record since 1906 of 29.1 Celsius , I'm not so sure, but we certainly will get close to it"
