The heatwave is continuing today with temperatures to reach as high as 31 degrees in parts.
A status orange warning is in place for Cavan, Monaghan, south Leitrim, Roscommon, Longford and Westmeath, while the rest of the country is under a similar status yellow alert.
Both will run until Friday.
It comes as parts of the world are experiencing severe weather events like flooding in Germany and high temperatures in Canada due to climate change.
Paul Downes from Met Eireann says it will start to cool down towards the weekend:
⚠? Met Eireann has issued a Level Orange severe weather alert (High Temps) for Monaghan. Valid from Tue. 20/07 @ 2PM until Fri. 23/07 @ 9AM, see https://t.co/ZROEtnTQ4T #WeatherWarning https://t.co/eu3I5C5Gul
— Monaghan County Council (@MonaghanCoCo) July 20, 2021
Meanwhile, the UK Met Office has issued an amber warning for extreme heat for Northern Ireland. That warning is in place from 8am on Wednesday to Friday night.
The Department of Agriculture has appealed to people to be aware of the risk of forest and scrub fires. It's issued a Condition Orange warning due to the dry weather and controlled burning is now banned.
The HSE has issued advice to help prevent heat exhaustion and heat stroke.
People are advised to ensure central heating is off, stay out of the sun between 11am and 3pm, stay hydrated, and keep drinks in the fridge.
Babies and children, people over 65, and people with underlying conditions are most vulnerable.
People are advised to seek medical help if they experience any signs of dehydration such as dizziness, drowsiness, or a racing heart.