A Status Yellow Thunderstorm warning is now in place until 9pm for all of Leinster, along with Counties Cavan, Monaghan, Cork, Limerick, Tipperary and Waterford.
Met Éireann said there will be heavy downpours as thunderstorms develop, with hail also possible.
The forecaster warned road users to take caution as there will be difficult traveling conditions, poor visibility and spot flooding.
Elsewhere, Met Éireann said showers will develop in other parts of the country from morning, becoming heavier and more frequent in the afternoon and evening.
It forecast temperatures of 15 to 19C in light winds with the best of any dry weather in Connacht.
Heavy showers and isolated thunderstorms will continue tonight and will ease and become less frequent overnight.
Tomorrow will see a cloudy start with scattered showers that will be lighter than previous days, turning into light rain and drizzle in the evening.
Meanwhile, the UK Met Office issued a Yellow thunderstorm warning for Antrim, Armagh, Down, Fermanagh, Tyrone and Derry yesterday.
The warning came into force at 8am this morning and will be in place until 9pm.
