"Coastal flooding still expected in some areas on Saturday around times of high tide," it said.
By late Friday, the storm was about 250 miles southeast of Nantucket, Massachusetts, with maximum winds of 50 mph.
Despite the change in the storm's status, its impacts are expected to remain the same. That means coastal flooding from the mid-Atlantic to southeastern New England, the hurricane center said.
"Weakening is forecast during the next couple of days, and Melissa is expected to become a remnant low by Saturday night or early Sunday," the NHC said.
CNN's Judson Jones contributed to this report.