Environment Canada has issued a humidex advisory for Ottawa, Gatineau and much of eastern Ontario, saying high heat and humidity are expected to make for "very uncomfortable conditions."

Temperatures Wednesday — when summer officially arrives — are expected to be in the low to mid 30s with humidex values exceeding 40 for the National Capital Region as well as all of southern Ontario, Environment Canada said.

Those conditions are expected to continue into Thursday, with night-time temperatures not expected to drop below 22 degrees Celsius in most areas.

"This will make for very uncomfortable conditions," Environment Canada said, and people should stay in an air conditioned place or seek shade when possible, drink plenty of water and limit physical outdoor activity.

"This is a good old fashioned heat wave," said CBC Ottawa climatologist Ian Black. "It will feel like a tropical jungle out there."

Heat warning issued Monday

The advisory follow a similar warning from Ottawa Public Health, which Monday issued a heat warning.

The city's medical officer of health warns infants, young children, the elderly, people taking medications like anti-Parkinsons and antidepressants and the homeless are at greater risk from extreme heat.

To avoid heat-related illness, residents and visitors are also advised to:

• Drink plenty of fluids, preferably water and avoid caffeine and alcohol
• Avoid strenuous physical activity outdoors
• Avoid direct exposure to the sun and seek shade and shelter at the first signs of heat exposure
• Wear lightweight and loose clothing
• Spend at least two hours a day in an air-conditioned location, including shopping malls, local libraries or neighbourhood community centres
• Never leave children, the elderly or pets unattended in a car, even with the windows partly rolled down

Ottawa paramedics spokesman J.P. Trottier said people can get into trouble if they ignore the warning signs.

"When people kind of push it, ignore the signs and symptoms. Push things a little bit too far," said Trottier. "And they get into heat exhaustion and worse case scenario heat stroke which is life threatening."

The heat and humidity is expected to break Friday.