A status yellow temperature warning comes into effect at 8am on Thursday morning.
It will expire on Saturday morning with highs in excess of 27 degrees expected.
Met Éireann is warning of the possibility for uncomfortable sleeping conditions and heat stress. There is also the possibility of isolated thundery downpours and spot flooding, the national forecaster warned.
The weather warning, due to “very warm and humid weather”, will expire at 8am on Saturday morning.
“Daytime temperatures in excess of 27 degrees in many areas away from coasts with night time temperatures not falling below 15 degrees,” Met Éireann said.
There will be highs of between 24 and 27 degrees on both Thursday and Friday.
Irish households are being asked to conserve water, as the spell of warm weather continues.
Uisce Éireann is appealing to the public to take practical steps as part of its Think Water Conservation campaign.
Over half of homes admit to wasting water, with usage in Dublin alone reaching up to 20 million litres a day in warm weather.
Head of water operations Margaret Attridge said making small changes can have a big impact.
Ms Attridge told Newstalk: "This campaign really is about trying to raise awareness with people that throughout Ireland people can make simple changes in their family homes. It's to raise awareness of those simple changes that people can make.
"Reducing a shower by even 60 seconds, you can save over 120 litres of water a week, if you're showering every day that's a lot of water that can be saved in a week."
Meanwhile, the HSE is reminding people of the importance of protecting their skin, with over 13,000 skin cancer cases recorded every year.
Selene Daly is a dermatology nurse at Sligo University Hospital. Ms Daly said: "Actually sunscreen is only one part of the sun smart code. It's wearing a hat, staying in the shade between 11am and 3pm, keeping a t-shirt on, wearing sun glasses, and wearing your suncreen as well.
"If you leave one part out you can fall victim to being sunburnt."
