The city is expecting heavy thunderstorms today followed by an extremely hot weekend according to Environment Canada.
Following today's (Wednesday) heavy showers - expected to peak at midday and reach the 30-50 mm range overall - Environment Canada has issued an extreme heat alert beginning Thursday.
A statement from the weather agency says a "persistent southwest flow is then forecast to develop, bringing hot and humid air from the Gulf of Mexico into Southern Ontario". Overnight temperatures will only fall to the low twenties.
A heat wave is usually defined as three consecutive days of temperatures in excess of 32 C. Environment Canada says heat warnings will be issued as the event draws nearer.
Global News Chief Meteorologist Anthony Farnell, says lakes and rivers in the area are still chilly, but that won't matter with the extremely hot and humid forecast.
The agency adds that it remains unclear when the heat will break. Symptoms of heat stroke and heat exhaustion include a high body temperature, lack of sweat, confusion, fainting and unconsciousness.
People in eastern parts of the country should brace for a sweltering Canada Day weekend.
The statement reminds the public to stay hydrated, rest frequently in shaded areas and dress in cool, loose clothing including a hat or umbrella for shade. Seniors, infants, young children, outdoor workers and athletes, people who are homeless and people taking certain prescription medications for conditions such as Parkinson's disease and depression are at the greatest risk of suffering from heat-related illness. The record for warmest Canada Day in Ottawa history is 36.7C, set in 1963.