The status-yellow warning took effect at 6am on Sunday, with the country set to sizzle in daytime temperatures of more than 30 degrees Celsius over the next three days.
Daytime temperatures between 25 and 30 degrees are expected generally, with up to 32 degrees possible in places on Monday.
Nighttime temperatures are forecast to range between 15 and 20 degrees, making a tropical night – when temperatures do not dip below 20 degrees – likely.
The coming days will see if Ireland’s highest temperature on record — 33.3 degrees at Kilkenny Castle on June 26th, 1887 — is beaten.
Keith Lambkin, head of Met Éireann’s Climate Services Division, said climate change is increasing the odds of record-breaking temperatures.
“Due to climate change, we are expecting to see heatwaves become longer, more frequent and intense than in the past. This increase in heat, increases the odds of temperature records being broken,” he said.
Met Éireann meteorologist Paul Downes said the “sweltering heat” is owed to the transport of an airmass, which has recently brought “exceptional” temperatures to Europe, towards Ireland.
“While the high builds in on Friday and Saturday the high temperatures will range generally in the low to mid 20s,” he said.
“As the high begins to drift a little to the east on Sunday, temperatures will rise to mid to upper 20s, with temperatures possibly surpassing 30 locally on Monday.
“There is a little more uncertainty regarding Tuesday but it does look like it will be another hot day and perhaps as hot, if not hotter, than Monday.
Heat stress, forest fires, melting roads and power…
Mr Downes also warned that nighttime temperatures will be “very warm and humid” with temperatures on Sunday and Monday night not likely to fall below the mid to high teens.
“In some areas they may not fall below 20 degrees, which is known as a tropical night,” he added.
The heatwave is likely to “break down” on Tuesday night into Wednesday, Mr Downes said, “as the low pressure system moves up over Ireland steering in cooler air from the west for the rest of the week.”
The short but intense heatwave has prompted warnings over risks including sunburn, heat stress, forest fires, melting roads and power cuts.