Environment Canada has issued a warning for a multi-day heat event for the GTA and all of southern Ontario starting Sunday. The national weather service says people can expect daytime highs ranging between 30 and 34 C with a humidex that will make it feel like 42.There won’t be much relief from the heat at night with lows ranging between 19 and 23 C. All of southern Ontario, along Lake Erie and Lake Ontario, is expected to feel the effects of the heat wave“The hottest conditions are expected on Monday,” Environment Canada says, adding the duration of the heat event remains uncertain in some regions. “In central Ontario, the heat event may end Monday night. Over some areas, the heat event could persist into Wednesday.”Wildfire smoke could also move back into the GTA starting Monday, mixing with hot and humid conditions.It’s yet another heat warning for Ontario this summer, where last month temperature records in many parts of the province were broken during an extreme heat wave.