MEXICO CITY (Reuters) -Hurricane Hilary strengthened into a major category 3 storm on Thursday as it barreled through the Pacific towards Mexico's Baja California peninsula, packing winds of up to 120 miles per hour (195 km per hour), the U.S. National Hurricane Center said.

It was moving west-northwest at near 14 mph (22 kph) and was forecast to approach the peninsula - which includes the popular tourist area of Los Cabos - over the weekend, the center said.

Additional strengthening is forecast for the next days and the storm likely to become a category 4 on Saturday, it added.

Hilary is expected to dump 3-6 inches (7.6-15 cm) of rain across parts of the Baja California peninsula through Sunday night. Flash flooding will be possible in some areas, the NHC warned, as well as "life-threatening" rip current conditions.

Tropical storm conditions are expected in the south of Baja California by late Friday, and are possible further up the peninsula by early Saturday.

The heavy rainfall was expected to impact the southwestern United States from Friday through early next week, peaking on Sunday and Monday.

(Reporting by Valentine HilaireEditing by Frances Kerry, Isabel Woodford, Alistair Bell and Lincoln Feast)