Hurricane Hilary is expected to intensify into a lashing Category 4 storm as it advances toward Mexico's Baja Peninsula on Friday and threatens to bring rain and flooding to parts of the Southwest US as it weakens over the weekend.

Hilary was churning about 430 miles south of Cabo San Lucas, Mexico, Thursday night with sustained winds of near 125 mph, the National Hurricane Center said in an overnight advisory.

The storm strengthened to a Category 3 hurricane Thursday evening and is likely to build into a powerful Category 4 on Friday, the advisory said. It is then expected to begin weakening as it continues north on Saturday.

Hilary's center is on track to approach the Baja Peninsula on Friday and over the weekend, prompting Mexican officials to issue a hurricane watch and tropical storm watches and warnings for parts of Baja California Sur, the hurricane center said.

There remains a wide range of outcomes for the heaviest rain and strongest winds in the US as the storm moves north over the next couple of days along Mexico's Baja Peninsula. Small deviations in the hurricane's track could change the forecast for the most intense rain and wind.

The storm is expected to substantially weaken before reaching Southern California and parts of the Southwest but there's an increasing chance the regions will be significantly impacted by heavy rain and flooding.

Heavy rainfall is expected to begin impacting the Southwest on Friday and through early next week, with the most intense downpours likely on Sunday and Monday, according to forecasters.

Southern swaths of California and Nevada could see 3 to 5 inches of rain with isolated amounts of up to 10 inches. Smaller amounts of 1 to 3 inches are expected across central parts of those states as well as across western Arizona and southwest Utah.

If Hilary makes landfall in California as a tropical storm, it will be a rare occurrence -- the first such storm there in nearly 84 years and would be only the third tropical storm or stronger to do so on record, according to data from the National Oceanic and Atmospheric Administration.