Humidex values approaching 40 C, 104 F are expected Tuesday and again Wednesday, as a blast of hot and humid weather has triggered heat warnings across most of southern Ontario.
Environment Canada said conditions Tuesday night are unlikely to provide much relief from the heat, with temperatures around 20 C, 68 F.
Health Protection Supervisor with Lambton Public Health Jessica Zehnal said heat warnings are issued when there's the risk for heat related illnesses, including heat stroke.
"Symptoms of heat related illnesses can include, rapid breathing, dizziness, fainting, vomiting, rapid heart beat, extreme thirst and decreased urination with dark yellow urine," she said. "Anyone experiencing these symptoms should move to a cool area to rest and rehydrate."
Zehnal said residents are encouraged to check on older family and friends, and seek a cool place.
"There are several cooling centres set up throughout the county, including centres in Sarnia, Petrolia, Brooke-Alvinston, Lambton Shores, Mooretown and Warwick Township," said Zehnal.
A complete list of the cooling centres is posted on the health unit's website.
Environment Canada Meteorologist Steven Flisfeder said there's the potential for the heat to stick around into Friday and Saturday.
"Most of the heat events we've been having have been two or three days," said Flisfeder. "This one is looking like at least four days, potentially five or six. So, that longer duration that poses an extra level of risk with this heat event."
- With files from Josh Boyce