While coastal areas can expect cooler conditions, overnight lows will struggle to fall between 18 or 19 C degrees.
The sticky humid air mass is expected to leave the region by Friday, which will lead to more comfortable temperatures on that day and into the weekend. "Humidex values will be in the mid to high thirties today, and near low forties for Wednesday and Thursday".
"People waking up Tuesday morning might feel a bit of relief from the extreme heat of the weekend, but it is only a short cooldown", she said.
The heat is hanging in there but take heart - it was a mere 18 C at dawn Tuesday and daytime highs will stay in the 20s by Friday.
Canada Day crowds in the capital will face the challenge of keeping hydrated in temperatures that are forecast to peak at 36 C, with a humidex of 47 and a UV index of 10, or "very high".
They planned to visit thousands more as the heat was expected to continue until Friday.
"This will be the most significant heat event in the past few years", according to Environment Canada.
Drouin says the victims fit the profile of people authorities describe as at risk: those with chronic illness or mental-health problems, people who live alone and people without air conditioning at home. "And also keep in mind to make sure you don't leave any people or pets in your auto, as temperatures will rise dramatically within minutes". Watch for the effects of heat illness: swelling, rash, cramps, fainting, heat exhaustion, heat stroke and the worsening of some health conditions.
The hot temperatures and high humidity are expected to persist through at least Thursday, Environment Canada said.