A Status Yellow warning has been issued for eight counties as temperatures are forecast to hit up to 30C in some areas.
Met Éireann said temperatures above 27C, along with night time temperatures above 15C, are likely for Clare, Kerry, Limerick, Tipperary, Galway, Kilkenny, Laois and Offaly.
It said the high temperatures could lead to heat stress, difficult sleeping conditions and water safety issues due to increased use of lakes and beaches.
Forest fires are also a possibility.
The warning will be in effect from 12pm this afternoon until 6pm tomorrow.
Earlier, Met Éireann Meteorologist Holly O'Neill said the highest temperatures are likely to be in the midlands and southwest.
A temperature of 28.6C was recorded at Shannon Airport in Co Clare yesterday, breaking the previous May record of 28.4C which was set at Ardfert in Co Kerry on 31 May 1997.
Speaking to RTÉ News, Ms O'Neill said there is a chance that the temperature record could be broken again.
"It is possible. We did have a provisional record-breaking temperature recorded at Shannon Airport yesterday at 28.6 degrees, which is lovely and warm for May," she said.
"Today, the temperatures are forecasted generally to be in the range of 23 to 29 degrees, even possibly getting up to 30 degrees in some places.
"There is absolutely a chance that that record will be broken again, but we'll just have to wait and see how today goes."
Any mist or fog patches😶🌫️ will clear early on to leave another generally warm or hot day🥵 and it'll be dry and sunny for most☀️.
— Met Éireann (@MetEireann) May 26, 2026
Highest temperatures🌡️ of 23 to 29 or 30 degrees, hottest in Munster and south Leinster. pic.twitter.com/ALLTnaRNf2
Met Éireann said it will be "another warm or hot day and it'll be dry and sunny for most".
However, it will be a little cooler in parts of the north and northwest of the country and will be cloudy for a time in these areas.
A so-called "heat dome" of warm air from northern Africa trapped under a high-pressure system over western Europe is behind the high temperatures not usually seen until high summer.
The "hot spell" will continue into tomorrow, Met Éireann said, with temperatures ranging between 22C and 29C or 30C.
It will be hottest in the midwest and west, but a little lower in coastal parts of the east and northeast.
Temperatures are set to drop to between 18C and 24C on Thursday, and into the low 20s into the weekend.
Ms O'Neill encouraged people to stay "sun-smart" during the spell of hot weather.
"The UV over the next few days is going to be quite high, so we're asking people to be sun-smart," said Ms O’Neill.
"Wear sun cream, seek shade if you are out and about during the day.
"Stay hydrated as well, most importantly, and also follow any water safety guidelines from safety Water Safety Ireland, if you are out and about on the water," she added.
The Irish Cancer Society also reminded people to protect their skin from harmful ultraviolet rays, the main cause of skin cancer.
Watch: Met Éireann's Gerry Murphy says new record temperature for May set yesterday
Michelle Lonergan, cancer awareness nurse at the charity, said simple steps can make a "huge difference in reducing" risk.
These include regularly reapplying a broad-spectrum sunscreen with a high SPF (30 or above), and wearing lightweight long sleeves, sunglasses and a wide-brimmed hat.
The Irish Blue Cross is also urging pet owners not to walk dogs during hot weather.
The charity says exercising dogs in temperatures above 20C can put them at serious risk of heatstroke, particularly flat-faced breeds such as pugs and bulldogs, as well as overweight pets.
The group is also warning owners never to leave dogs in parked cars, even for a short time or with windows partly open.
Veterinary experts say heatstroke can develop quickly and may lead to seizures, organ failure or death if not treated immediately.
Cat owners are also being reminded to check sheds, greenhouses and sunrooms before closing them, as animals can become trapped in warm conditions.
Additional reporting: Dónal Ryan, PA
