The yellow alert for high temperatures kicks in for 12 counties at lunchtime today and lasts until Sunday morning.
Temperatures of around 27 degrees are expected during the day, falling no lower than 15 degrees at night.
People are urged to stay hydrated, wear sunscreen and be careful of glaring sun while driving.
The warning applies to Carlow, Kildare, Kilkenny, Laois, Limerick, Longford, Meath, Offaly, Tipperary, Waterford, Westmeath and Wexford.
It will apply between 1pm on Friday and 7am on Sunday.
It comes on top of a general warm weather advisory for the entire country which began on Wednesday and continues until Tuesday.
Dog Hogan cooling off whilst enjoying the sunny weather on Balscadden Bay, Howth. Photo: Sam Boal/Collins Photos
The UV Index is also expected to be high to very high, with Met Éireann advising of further possible “tropical nights” over the weekend and some thunderstorms.
Met Éireann's forecast for Friday reads: "A very...
