The first ever amber extreme heat warning is being issued to large parts of Wales, with temperatures soaring above 30°C.
It follows a weekend of weather records with temperature gauges reaching 30.2°C in Cardiff, and 29.6°C in Usk in Monmouthshire on Saturday.
Forecasters say temperatures could even reach 33°C in some western areas of the UK as the week progresses.
High nighttime temperatures are also expected which could have potential health risks for those who are vulnerable.
The Met Office is urging people to keep out of the sun between 11am to 3pm, drink plenty of fluids and apply sunscreen.
People are also being advised not to drink excessive amounts of alcohol and to avoid exercise outdoors during the hottest parts of the day.
However the Chief Operational Meteorologist at the Met Office says the unusually high temperatures are likely to persist but should decrease later on in the week.
"Temperatures should begin to fall for most areas heading into the weekend, with some more unsettled conditions looking to develop."
For more on the forecast click here for the weather.