Tropical Storm Barbara was strengthening Sunday off the southwest coast of Mexico and was expected to become a hurricane overnight but without menacing land, the National Hurricane Center in Miami said.

Barbara was located about 205 miles south-west of the touristic port of Zihuatanejo in Guerrero state, according to the center. It had maximum sustained winds of 60 mph, and was moving west-northwest at 12 mph. No coastal watches or warnings were issued.

The storm is expected to become a hurricane overnight as it continues to move west-northwest for two more days, before turning toward west at a slower forward speed into the Pacific by Tuesday, forecasters said.

Barbara formed off the southwest coast of Mexico earlier Sunday.

Heavy rainfall totals of 2 to 4 inches are possible across portions of the Mexican states of Guerrero, Michoacan, Colima, and Jalisco through Monday. This rainfall may lead to flooding and mudslides.

Swells affecting portions of the southwestern Mexico coast for the next few days can produce life-threatening surf and rip current conditions, the hurricane center said.