Tropical Storm Marie is seen south of Mexico's Pacific coast on August 22, 2014

Tropical Storm Marie has formed in the eastern Pacific and is expected to become a hurricane this weekend that will stalk the Mexican coast, US forecasters warned Friday.

Packing of 50 miles (85 km) per hour, the weather system was "strengthening steadily" and predicted to cause life-threatening surf and along Mexico's coast over the coming days.

"Marie is likely to become a hurricane by early Saturday," the National Hurricane Center said.

The storm was currently swirling 325 miles south of the Mexican resort of Zihuatanejo, the Miami-based center said in its 1500 GMT advisory.

No coastal watches or warnings have been issued so far.

Meanwhile, Hurricane Lowell—the seventh of the season in the Pacific—lost steam and was downgraded to a tropical storm.