Hurricane Cristobal is expected to move rapidly toward the north Atlantic, staying away from Bermuda and passing south of Nova Scotia.
The Canadian Hurricane Centre in Halifax says the storm is racing northeastward toward the Grand Banks off Newfoundland.
It's packing maximum sustained winds of 120 km/h.
Cristobal is expected to stay out at sea, but the centre says it will merge with a slow-moving cold front that's passing over the Atlantic provinces.
Forecasters say the combination could result in wind and rain in excess of 50 millimetres in parts of Atlantic Canada, starting Thursday and continuing Friday.
Ocean swells are expected along coastal areas of Nova Scotia and southern Newfoundland.
"There is going to be some larger swells but, as well, the possibility of rip [currents] at our beaches, so be very aware of that. A rip [current] is a very fast-moving flow of water that develops and could take you out to sea, rather than in to shore,” cautions CBC meteorologist Peter Coade.
If a swimmer becomes caught in a rip current, it's best not to tire oneself out attempting to swim back to shore. Swimmers should stay calm and swim parallel to shore to get out of the narrow, fast-moving current, then swim back to shore.
Hurricane Cristobal hurled heavy rains across Atlantic and Caribbean islands on Tuesday as it headed toward Bermuda, and the storm has been blamed for at least five deaths.