A heat warning is in effect for the City of Toronto and across the GTA on Tuesday, with temperatures expected to feel like 34 C.

The heat warning, issued Monday by Environment Canada, remains in effect for Toronto, Vaughan, Richmond Hill, Mississauga, Markham, Oshawa and Hamilton.

The UV index is at 9, which is very high, according to Environment Canada.

The city’s medical officer of health reminded residents to drink plenty of liquids before they feel thirsty, as thirst is a poor indicator of dehydration.

“The public is encouraged to call or visit family, friends and neighbours, especially isolated adults and seniors who are at greater risk of suffering from heat-related illness, to make sure they are cool and drinking plenty of fluids,” a news release issued Tuesday said.

“Other groups at risk include people with chronic illnesses, individuals with limited mobility or certain mental health illnesses, infants and young children, people on certain medications and those who are homeless.”

The warning also advised that members of the public stay in air-conditioned spaces, wear lose, light coloured clothing when outdoors and to reschedule or plan outdoor activities during cooler parts of the day.

The city is not expected to see temperatures cool down until Friday.