A new tropical storm is expected to make landfall Sunday or Monday in Mexico, already reeling from this year's hurricane season.

Fast-moving Sonia, spinning in the Pacific Ocean some 250 kilometers (155 miles) south of Baja California's tip, will pass below the peninsula later today and approach mainland Mexico, according to the Miami-based US National Hurricane Center.

A tropical storm warning was in effect for a stretch of the coast reaching from Altata to Mazatlan, in Sinaloa state.

Sonia was moving at 20 kilometers per hour with maximum sustained winds of 75 kilometers per hour.

The storm was expected to dump eight to 15 centimeters (three to six inches) of rain across parts of Mexico's western coast in Sinaloa and western Durango with isolated areas receiving up to 25 centimeters, according to the Miami-based storm center.

Mexico's National Meteorological Service estimated the strong to torrential rain could reach a total of nine states and create waves two to three meters (yards) high.

"These rains may produce life-threatening flash floods and mudslides," the US hurricane center said.

In mid-September, Tropical Storm Manuel struck Mexico's western coast while another system, Ingrid, slammed the opposite side of the country almost simultaneously.

The twin storms claimed 157 lives and damaged the homes of 1.7 million people.

Sonia is the eighteenth named storm this hurricane season, which runs from the beginning of June through the end of November.