A special weather statement was issued on Wednesday that humidex values are expected to reach over 35 C.
CBC Meteorologist Ryan Snoddon said it's lining up to be a record-breaking couple of days, with temperatures forecast near 30 C, and a humidex near 40.
"The July 30 record of 27.8 C set back in 1967 is sure to fall today," he said.
"Tomorrow's July 31 record of 29.3 C, set back in 2004, will also likely be broken."
Snoddon said the 30-degree mark at the St. John's weather station is tough to come by — it has reached that mark just nine times over the past 72 years.
"A couple of other records I'm keeping an eye on are the all-time temperature record of 31.5 C and the all-time humidex record of 38.5 at St. John's YYT," Snoddon said.
"Both records were set on the same date, back on July 6, 1983, and are certainly at risk of being broken over the next two days."
Warm, humid air mass over most of Newfoundland
Meteorologist Allison Sheppard, who works with the Gander weather office, said a warm, humid air mass will remain over much of the island for the next 48 hours.
"There are several areas that have values into the high 30s, but it looks like through Gander, in through St. John's, they're going to be in the very high [range], approaching 40 for humidex values."
The heat and humidity will affect the following areas:- Avalon Peninsula North
- Bay of Exploits
- Bonavista North
- Bonavista Peninsula
- Buchans and the interior
- Clarenville and vicinity
- Deer Lake - Humber Valley
- Gander and vicinity
- Grand Falls-Windsor and vicinity
- Green Bay - White Bay
- St. John's and vicinity
- Terra Nova
Environment Canada reminds anyone taking part in strenuous outdoor activities over the next two days to drink plenty of fluids to remain hydrated, and suggests rescheduling outdoor activities to cooler parts of the day.