Met Éireann has issued a yellow heat warning for 12 counties on Friday, with temperatures of up to 30 degrees forecast.
The warning applies to Carlow, Kildare, Kilkenny, Laois, Longford, Meath, Offaly, Westmeath, Wexford, Limerick, Tipperary and Waterford from 10am on Friday until 7am on Saturday.
The weather agency warned of water safety issues, heat stress and uncomfortable sleeping conditions as a result of the high temperatures.
The warning comes on top of a general warm weather advisory for the entire country, which began on Wednesday.
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Moore Park in Co Carlow reached a high of 27 degrees on Wednesday, the fourth consecutive day of 25 degree-plus values.
Temperatures will remain above 25 degrees in many areas on Thursday.
The warmest weather on Thursday and Friday will be in the southern half of the country with a strong northerly breeze keeping temperatures notably cooler elsewhere, though it will still feel pleasant with temperatures in the low 20s.
Temperatures between 24 and 28 degrees will be experienced across the midlands, south and east on Thursday, and Friday will be even warmer, with highs between 27 and 30 degrees.
The same pattern will repeat itself over the weekend, though an easterly breeze on Sunday will keep temperatures along the east coast slightly lower than of late.
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The warm air will then spread northwards on Sunday into Monday and north Connacht and Ulster will experience very hot weather.
Met Éireann forecaster Deirdre Lowe said the hot spell will continue for the foreseeable future, which is towards the end of next week.
“It might even get warmer next week. It’s going to be very muggy and humid too,” she said. “We could see a few records broken.”
Explainer
What is an official heatwave in Ireland?
Thursday of next week is looking exceptionally hot, especially in Munster.
Heatwave events are relatively rare in Ireland and two in a summer rarer still. The last time there were two in a summer was in 1976, which was one of the warmest and driest on record.
The longest recorded heatwave in Ireland was at Kilkenny in 1995, which recorded 27 consecutive days with temperatures above 25 degrees.
The longest nationwide heatwave was 14 days in the summer of 1976.
The current spell of warm weather is being created by a ridge of high pressure known as the Azores high, which has settled over the country, though not far enough to drive away patches of clouds in the northernmost parts of the country.
From Friday, high pressure is expected to shift to the north of Ireland, with support from the upper air pattern. This will allow temperatures to increase, and the sunshine to become more widespread.
