The forecaster also said that additional intensification is expected over the next 12 hours, followed by a weakening before it becomes a post-tropical cyclone on Tuesday.
Hurricane Ernesto is about 815 miles (1,312 km) southwest of Newfoundland, Canada, and has maximum sustained winds of 75 mph (120 kph), according to the latest update.
The center of Ernesto will pass near southeastern Newfoundland late Monday into Tuesday morning, which could bring wind, waves and rain, NHC added.
Ernesto is the fifth named Atlantic storm of what is expected to be an intense hurricane season.
Hurricane Ernesto made landfall on Puerto Rico and the U.S. and British Virgin Islands last week. The Caribbean island's main power supplier LUMA Energy said more than 725,000 homes and businesses lost electric service after the heavy rainfall.
The Category 1 storm then moved to Bermuda, knocking out power, downing trees and flooding parts of the island on Saturday, but officials have said the British island territory seemed to have escaped any major damage.