MIAMI -- Tropical Storm Humberto is strengthening some as it moves west across the Atlantic, south of the Cape Verde Islands and could eventually become a hurricane.

The storm’s maximum sustained winds Monday afternoon are near 45 mph. But the U.S. National Hurricane Center says Humberto is expected to strengthen and could become a hurricane on Wednesday.

A tropical storm warning is in effect for the southern Cape Verde Islands of Maio, Santiago, Fogo and Brava.

The storm is centered about 85 miles south of Praia in the Cape Verde Islands and is moving west near 12 mph.