The warm summer weather is set to continue through Wednesday, although cooler and cloudier conditions have set in across the west and southwest of the country.
While temperatures today will continue in the 20s, and expected to hit 24 degrees in parts of the east, temperatures in the west will fall to between 17 and 20 degrees.
Met Éireann has forecast outbreaks of rain which will gradually move across the western half of the country with thundery bursts in some places, particularly on Atlantic coasts.
Thursday will be dry with sunny spells but temperatures will fall slightly with highs of 21 to 22 degrees. Showers are expected to develop through the afternoon, particularly in the western half of the country.
The warm weather will continue on Friday but temperatures will drop slightly over the weekend to the high teens.
Forecaster Klara Finkele says this week's warm and humid weather has risen up from the Bay of Biscay and continental Europe where some countries have experienced temperatures in excess of 40 degrees in recent days.
Ms Finkele warned that the high levels of humidity across the State would bring a risk of thunderstorms and heavy downpours.
“Weather from the Bay of Biscay tends to be quite unstable, it’s warm and very moisture laden so we’re certainly going to keep an eye on the rain,” she said.
“Warm air holds more humidity and moisture so it can lead to heavy downpours.”
A number of European governments have issued weather warnings as a heatwave sweeping through Portugal, Spain and France has pushed temperatures above 40 degrees. Paris has activated its national heatwave emergency plan while French authorities have set up a heatwave register in some towns to check up on isolated elderly people.
In the UK, temperatures in parts of London had already reached 29.4 degrees by 9am on Wednesday, with reports that it could be the hottest day in nine years.
The Irish Cancer Society has urged people to take care in the sun, particularly the elderly and young children.
Parents are advised to dress babies under six months in loose-fitting clothes with long sleeves and to keep them in the shade as much as possible.
Children should wear hats and sun glasses in the sunshine and use sunscreen with SPF 30 or higher. Sunscreen should be reapplied every two hours.
Adults are also advised to spend time in the shade, wear a hat and sunglasses, and to use sunscreen with SPF 15 or higher.
Pets should be kept well hydrated during the spell of hot weather.
Kathrina Bentley of Dogs Trust Ireland warned against travelling with your pet in the car.
“Don’t drive with your animal in the car. It’s the equivalent of keeping them in the oven as their fur keeps the heat in longer. Keep lots of water bowls around the house and avoid exercising your pet between noon and 3pm as this is when the weather is warmest,” she said.
Additional reporting from PA