MEXICO CITY (Reuters) - Hurricane Rosa intensified into a major storm in the Pacific Ocean, with maximum sustained winds near 145 miles per hour (230 kph) and little change in strength was expected overnight, the U.S. National Hurricane Center (NHC) said late on Thursday.

Rosa, a Category 4 storm on the five-step Saffir-Simpson Hurricane Wind Scale, was about 605 miles (975 km) southwest of the southern tip of Baja California and moving west at almost 9 mph (15 kph).

It is the seventh category 4 hurricane of the season.

“Little significant change in strength is forecast overnight, with some slow weakening anticipated by Saturday, and a larger decrease in wind speed expected early next week,” the NHC said in its advisory.

Swells generated by Rosa are forecast to affect parts of the coastlines of southwestern Mexico, the southern Baja California Peninsula, and southern California later this week and over the weekend.

“These swells are likely to cause life-threatening surf and rip current conditions,” the Miami-based center said.

However, no coastal watches or warnings are in effect, the NHC said.