MIAMI -- Hurricane Lorenzo is back to being a Category 4 storm in the central Atlantic Ocean after several hours as a Category 5 -- which made it the strongest storm ever observed so far north and east in the Atlantic basin.

The U.S. National Hurricane Center said early Sunday that the storm has maximum sustained winds of 155 mph (250 kph).

Lorenzo is moving north at 10 mph (16 kph) and is centred about 1,360 miles (2,190 kilometres) southwest of the Azores, a Portuguese island chain.

There are no coastal watches or warnings currently in effect, although forecasters expect the storm to remain strong as it approaches the Azores over the next few days.

Officials say swells produced by the storm are currently affecting parts of the northeastern coast of South America and the Lesser Antilles.