Environment Canada meteorologist Jean-Marc Couturier said the two likely will not merge, but rather Leslie is expected to overpower Michael and push it out of the area.
"As they would get in the same area, they probably would compete, so one would win over the other," said Couturier from Halifax.
He said Leslie covers a much larger area than the Category 2 hurricane Michael and will likely weaken the storm when they both arrive in the southeastern part of the province.
"Probably Leslie would become the main system and would probably at that point slow down and would... steal away some of the energy that would be required to keep Michael alive and going," said Couturier.
Couturier said Leslie is tracking toward Atlantic Canada, but is expected weaken as it approaches the Grand Banks and will then brush the southeastern part of the Avalon Peninsula as a tropical storm.
He said rainfall will likely be the biggest threat rather than high winds, although it's difficult to predict rainfall amounts.
The threat of Leslie hitting Nova Scotia continues to decrease, said Couturier.
"The chances for Nova Scotia are slim. For the eastern half of Nova Scotia we'd see... a probability of 10 per cent of getting some impact."
However he said the storm is still expected to produce two-metre waves that could rise to three metres as they break near the shoreline, creating dangerous rip currents.
In Newfoundland, waves could reach up to nine metres on the province's south coast, said Couturier.
Residents of those provinces are being warned to be cautious along southern coastlines in the days ahead.
For the past few days, Leslie was stalled southeast of Bermuda, which has caused the storm to weaken.
Leslie was starting to track northward and was expected to become a Category 1 hurricane on Sunday as it moved over warmer waters.