Gaston -- which on Thursday became the third named hurricane of the Atlantic season but quickly weakened into a tropical storm -- has sustained maximum winds of 85 miles (140 kilometers) per hour, the Miami-based NHC said in its 0300 GMT Sunday bulletin.
The center of Gaston was located 655 miles east-southeast of Bermuda and was moving towards the northwest at a speed of eight miles per hour.
The hurricane was forecast to turn north on Monday, and the NHC's five-day forecast cone has Gaston then moving northeast and into the open Atlantic by Thursday.
The NHC issued no coastal watches or warnings, though it did warn that Gaston was expected to strengthen during the next 48 hours.
Gaston's hurricane-force winds extend outward up to 15 miles from its center, and its tropical-storm-force winds extend outward up to 140 miles.
The Climate Prediction Center of the National Oceanic and Atmospheric Administration (NOAA) initially estimated the Atlantic would see between 10 and 16 storms this year, but recently updated its prediction to 17.
The eight-week stretch between mid-August and mid-October is the most active period for storms and hurricanes in the Atlantic, according to the NHC.
"The statistical peak day of the hurricane season - the day you are most likely to find a tropical cyclone somewhere in the Atlantic basin - is September 10th," the Hurricane Center website says.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.