Hurricane Katia has weakened to a Category 1 storm as it churns west across the Atlantic, with sustained winds of roughly 130 km/h.
The storm was located about 535 kilometres west-southwest of Bermuda late Wednesday afternoon, the U.S. National Hurricane Center said.
Katia was moving northwest at about 17 km/h and was expected to pass "between Bermuda and the East Coast of the United States" Wednesday night and Thursday, forecasters said.
The hurricane centre said the core of the storm is not expected to make landfall, but large swells would affect parts of the U.S. East Coast, Bermuda and the Greater Antilles.
"These swells are likely to cause life-threatening surf and rip-current conditions," forecasters said.
The Canadian Hurricane Centre issued a statement Wednesday saying that forecasts suggest Katia could make a "sharp eastward turn on Friday."
"That would result in impacts limited to the offshore district but with at least large waves reaching the southern coastlines of Nova Scotia and Newfoundland," the hurricane centre said.
Two-metre swells expected on Canadian Atlantic coast
The centre expects swells of two metres or more Thursday and Friday, with waves breaking at three to four metres in some locations.
"Dangerous surf and riptide conditions will occur and spectators should stay well away from the wave-breaking zones," the centre said.
Meanwhile, tropical storm Nate has formed in the Gulf of Mexico, and authorities have issues a tropical storm warning for parts of Mexico's coast.
The U.S. hurricane centre said Nate could become a hurricane by Friday.
Also, tropical storm Maria was swirling in the western Atlantic, but it was still far from land and was not expected to strengthen over the next couple of days.