Met Éireann has issued a Status Yellow high temperature warning for tomorrow and Saturday with highs of over 27C expected. The alert for counties Carlow, Dublin, Kildare, Kilkenny, Laois, Longford, Louth, Meath, Offaly, Westmeath, Cavan, Monaghan, Roscommon, Tipperary comes into effect at midday tomorrow and is set to expire at 6am on Saturday. A Status Yellow high temperature warning for the entire country will then come into force at midday on Saturday until 6am on Sunday. Forecasters have warned that temperatures could reach in excess of 27C during the day and not drop below 15C at night. The hottest day of the year and the hottest day in Ireland for three years was recorded last month in Co Roscommon. The mercury hit 29.6C at Mount Dillon on 20 June. Met Éireann said it was the highest temperature recorded since August 2022. The HSE said those most at risk during hot weather include: Babies and young children People over 65 and those with underlying health conditions, including heart and breathing problems as well as Alzheimer's disease and dementia People who spend a lot of time outside or in hot places - such as those who work outdoors or the homeless - are also at high risk. The advice for staying cool indoors is: Turn off lights and appliances not in use as they generate heat Close windows that face the sun during the day and open them at night when temperatures drop Close curtains in rooms that are exposed to the sun, sprinkle water over the skin, or keep a damp cloth on the back of the neck Use an electric fan (but only if the temperature is below 35C) Outdoors, people should: Stay in the shade Avoid being outside, if possible, between 11am and 3pm - the hottest part of the day Wear light and loose-fitting clothing that covers the skin Wear a wide-brimmed hat and sunglasses Regularly apply a UVA and UVB water-resistant sunscreen to skin that is not covered, using factor 30+ for adults and 50+ for children People are also advised to drink plenty of fluids. Water or oral rehydration sachets are considered the best option. Adults, on average, need about two litres of water over 24 hours, according to the HSE. People should drink enough during the day so that their urine is a pale clear colour.