A status yellow rainfall warning is in place for most of the country with the exception of West Connacht.
Between 25 and 50mm of rain could fall locally in short showers.
There is also a risk of flash flooding and lightning across the afternoon and evening.
People in Dublin are being warned to expect some heavy downpours this afternoon.
Forecasters say the capital could even see a thunderstorm ahead of the long weekend.
Met Éireann's Gerry Murphy is warning drivers there will be poor visibility during downpours in affected areas.
He said: "The potential impact of it is if you have very heavy downpours that mean visibility is significantly reduced for driving and there is the potential for some flash flooding to occur."
Earlier: There is a warning for thunderstorms and some spot flooding across the country today.
Met Éireann have issued a status yellow rain alert, which is in effect from 9 o'clock this morning until 10 tonight.
They say there could be extremely heavy rainfall in places, with up to 50mm falling in a short space of time.
- Digital Desk