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

Barbara was located about 170 miles southwest 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 was expected to become a hurricane as it moves west-northwest for two more days, before turning toward west 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, with amounts of up to 6 inches in limited areas, are possible across portions of the Mexican states of Guerrero, Michoacan, Colima, and Jalisco through today.

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.

— The Associated Press