Just when things were starting to cool down, summer is making a comeback.

The city of Ottawa has issued a heat warning — declared when Environment Canada forecasts a humidex of 40 C or more for at least two consecutive days — until further notice.

“Heat is hardest on the elderly and chronically ill. If they have no protection from the heat ... they can develop serious health effects and even die,” said Ottawa’s Medical Officer of Health Dr. Isra Levy.

Environment Canada also issued a humidex advisory. Yesterday, it felt like 41 C with the humidex, said meteorologist Geoff Coulson.

It’s unusual for weather like this to continue over a consecutive number of days this late in the season, Coulson said.