At 11 p.m. Monday, the hurricane was located 695 miles east-northeast of the Northern Leeward Islands and about 1,085 miles southeast of Bermuda. It was moving west-northwest at about 12 mph. Maximum sustained winds were measured near 120 mph.
Daniel Brown, a forecaster at the National Hurricane Center, said Bertha was expected to stay at roughly the same intensity for the next day or two.
"Conditions aren't going to change too much over the next couple days, so it will likely remain a strong hurricane," Brown said.
The hurricane center has projected 12 to 16 named storms in the Atlantic this season, with six to nine of them hurricanes.
The U.S. has not been hit by a major hurricane since 2005, the busiest season on record, which brought a destructive triple-punch of Katrina, Wilma and Rita ashore.
The Atlantic hurricane season runs through Nov. 30.