MIAMI (AP) — Tropical Storm Sam has formed in the Atlantic and is expected to become a major hurricane.

The U.S. National Hurricane Center says the storm’s maximum sustained winds Thursday were near 50 mph with additional strengthening expected. The storm is expected to be near major hurricane strength by the end of the weekend.

The storm was centered about 1,745 miles east-southeast of the northern Leeward Islands and was moving west about 16 mph.

Sam is the 18th named storm of an active hurricane season.