One of the longest heat waves so far this summer is expected for Windsor and Essex County, according to Environment Canada.

The national weather agency expects temperatures to reach 31 C on Tuesday, inching up to 34 C by Friday. The humidex is anticipated to hover around 40 this week.

With yet another heat wave coming, Environment Canada issued a heat warning for Chatham-Kent and Windsor and Essex County.

A hot air mass moving through the U.S. will become considerably more humid Tuesday night with overnight temperatures staying in the low 20s.

"This may be the longest and most significant heat wave of the summer so far," according to a statement from Environment Canada.

Temperatures will finally get back to more comfortable levels on Sunday with an expected 26 C, explained Geoff Coulson, warning preparedness meteorologist.

This summer has been particularly hot for southern Ontario. Windsor had 18 days with temperatures reaching 30 C or higher last year, compared to 22 days already this year.

The region averages 24 days higher than 30 C during the summer months.