Households have been asked to conserve water with temperatures due to hit highs of up to 28 degrees during the spell of warm weather.
The national forecast is for another dry and sunny day on Thursday, with highest temperatures ranging from 24 to 28 degrees.
A status-yellow high temperature weather warning has been put in place by Met Éireann, advising of very hot and humid weather over Thursday and Friday. The warning is to remain in place until Saturday morning.
Additionally, two separate yellow thunderstorm warnings have been issued, one for counties Leitrim, Roscommon, Sligo, valid until 8pm on Thursday and the other for Cavan, Monaghan, Longford, Louth, Meath, Offaly, Westmeath, which is valid until 6pm on Thursday. Frequent lightning can be expected during these warning periods.
While most of the country will be able to enjoy the sunny weather, there will be some rain in the southeast on Thursday, which will move northwards over Leinster.
Met Éireann said the rain may turn heavy in parts and even bring a risk of thundery showers and possible spot flooding in the east of the country.
The forecast for Friday is for another hot day with temperatures reaching highs of up to 28 degrees or more.
The weather will be dry for most of the country, with some fog along coastal areas and a threat of isolated heavy showers inland.
Saturday is expected to see bright and sunny spells with some scattered showers. Highest temperatures will be between 21 and 25 degrees.
[ 11 ways to adapt to the heat as Ireland experiences unseasonable warm spellOpens in new window ]
The forecast for Sunday is also for a warm day with sunny spells, but there will be some showers, which in places could turn to thunderstorms and bring a risk of spot flooding, the national forecaster has said.
The weather looks set to begin to cool next week, with highest temperatures dropping to 19 degrees or lower on Monday, and the rest of the week bringing even more unsettled weather and rain.
Siobhán Ryan, a meteorologist with Met Éireann, said the current high temperatures were “unusual” for September.
Ms Ryan said the sunny spell was an “early Indian summer” caused by a number of factors.
[ How to avoid sunburn, food poisoning, skin rashes and other summer ailmentsOpens in new window ]
The high and humid temperatures were likely the result of knock-on impacts from Hurricane Franklin, which passed Bermuda in recent days, as well as warm air flows moving up from Africa to Ireland, she said.
The highest temperature ever previously recorded in September was 29.1 degrees in Co Kildare in 1906.
This week the highest temperature hit was 27.6 degrees at Valentia observatory, Co Kerry on Monday, she said. “Even to get to 27 degrees is exceptional in September,” she said.
Uisce Éireann, the national water utility previously called Irish Water, has urged households to try to conserve water during the current spell of hot weather and beyond.
Margaret Attridge, head of water operations, said while it was great to see the current spell of sunny weather after a wet summer, it brought its “own unique set of challenges” for the utility company.
“Some urban areas tend to see increases in demand around this time of year as schools return and people come back to work after holidays,” she said.
“As we come into autumn and winter, storms and other extreme weather can impact on the capacity to treat and produce clean drinking water,” she said.
“For this reason, water conservation is something we should think about year-round, not just during the summer,” she said.
[ Too hot to cook? Heatwave-friendly meals without turning the cooker onOpens in new window ]
Ms Attridge said Uisce Éireann had been planning to conduct a public campaign reminding people to be conscious of their water use even before the current sunny weather.
“By working together to use only what we need in our homes, gardens, and businesses, we can all contribute to ensuring a sustainable water supply for everyone,” she said.
A spokesman for Uisce Éireann said despite the conservation advice, there was no concerns at present about water shortages.
The utility’s 700 water supplies were operating normally and “there are no plans to introduce general water restrictions or hosepipe bans,” he said.
“Following a warm and dry June, above average rainfall during July and August mean that most raw water sources are now at healthy levels,” he said.
