Kirk was about 835 miles (1,345 km) west-southwest of the southernmost Cabo Verde Islands and is moving westward about 25 mph (41 kph), according to NHC's 11 p.m. advisory. Kirk has sustained winds of 35 mph (55 kph). It was originally a tropical storm earlier Sunday.
NHC says it is possible that Kirk could degenerate into a trough of low pressure during the next day or two while it moves quickly across the tropical central Atlantic.
Kirk became the 11th named storm of the Atlantic hurricane season, which goes until Nov. 30.
Meanwhile, Subtropical Storm Leslie formed Sunday morning in the North Atlantic. Maximum sustained winds are near 40 mph (65 kph) with higher gusts. NHC says little change in strength is forecast during the next couple of days, and Leslie is forecast to be merge with a larger non-tropical low by the middle of the week.
Leslie was about 1,245 miles (2,005 km) west of the Azores, moving southwest at about 5 mph (7 kph).