Environment Canada meteorologist Simon Legault said there will also be a high degree of humidity as well.
He recommended staying out of the sun during peak hours, using an air conditioner, staying hydrated and not exercising too vigorously outside.
Today: A mix of sun and cloud. 40 percent chance of showers late this afternoon with risk of a thunderstorm. Fog patches dissipating early this morning. High 29. UV index 8 or very high.
Tonight: Partly cloudy. 40 percent chance of showers this evening with risk of a thunderstorm. Low 20.
Tuesday: Mainly sunny. High 29.
Check the longer-term forecast here.