Businesses boarded over windows and thousands of troops were put on alert Saturday as Hurricane Blanca roared toward Mexico's Baja California Peninsula as a powerful Category 3 storm.

The unpredictable Blanca, which strengthened suddenly from a Category 1 to a Category 4 storm on Saturday before weakening slightly, is expected to make landfall as a tropical storm on Monday. But authorities said its outer bands could start hitting the southern Baja California Peninsula as a hurricane on Sunday.

The director of Mexico's National Water Commission, Roberto Ramirez, said he was concerned by Blanca's "erratic" behavior and warned residents along Mexico's Pacific coast to be prepared for intense rains that could begin late Saturday or early Sunday, including in coastal states of Guerrero, Michoacan, Colima and Jalisco.

In Baja California, 2,000 army troops and 1,321 marines have been put on alert, as well as emergency responders and power line technicians, said Civil Protection director Luis Felipe Puente.

He said there is currently a 70 percent hotel occupancy rate in Los Cabos and warned tourists to be attentive to any advisories issued by authorities.

On Saturday, some businesses and banks were seen hammering boards over their windows in preparation for Blanca's arrival. People began forming lineups at gas stations to stock up on fuel.

Blanca's maximum sustained winds on Saturday afternoon were near 120 mph (195 kph), according to the U.S. National Hurricane Center. The hurricane is centered about 320 miles (510 kilometers) south of Cabo San Lucas and is moving northwest near 10 mph (17 kph).

A hurricane watch is in effect for an area from Cabo San Lucas to Santa Fe. A tropical storm warning is in effect from Loreto to Puerto San Andresito, including Cabo San Lucas.

Puente said he saw no reason to suspend local elections scheduled to be held on Sunday.