Laois and Offaly are among nine counties named by MET Eireann.
A status yellow thunderstorm and rain warning has been issued for this afternoon and evening by Met Eireann.
Counties most at risk are Laois, Offaly, Tipperary, Wicklow, Kildare, Clare, Galway, Mayo and Roscommon.
Meanwhile, temperatures are expected to remain in the mid 20s for the weekend.
Met Eireann forecaster Matthew Martin says people in the East are likely to be the first to experience cooler weather: