The fourth hurricane and fifth named storm of the season had top sustained winds of 85 mph (140 km/hr) by 11 p.m. AST/0300 GMT on Monday with higher gusts, and was forecast to strengthen further as it headed northwestwards over the central Atlantic.
The center of the storm was about 835 miles northeast of the Northern Leeward Islands and was moving toward the northwest at 15 mph (24 km/hr), the Miami-based hurricane center said.
"This will curve harmlessly out to sea. It's already far out at sea and should continue to stay out there," NHC spokesman Dennis Feltgen said late on Sunday.
So far this year, only one Atlantic hurricane - Arthur, a Category 2 storm, made landfall in the United States, on North Carolina's Outer Banks in early July.
In its August outlook, the NHC said cooler-than-average temperatures in the tropical Atlantic Ocean would make it difficult for larger storms to develop. REUTERS