A tropical storm watch is now in effect for certain areas of Southern California, including San Diego, Orange and Los Angeles counties. 

This marks the first-ever instance of a tropical storm watch being issued for this region of the U.S., according to the National Hurricane Center.

Hurricane Hilary, which turned into a powerful Category 4 storm overnight and is swirling in the Pacific Ocean near Mexico, is carrying very strong winds of about 145 mph and is expected to approach Mexicos Baja California Peninsula on Saturday night as a hurricane and turn into a tropical storm before reaching Southern California on Sunday, the National Oceanic and Atmospheric Administration reports. 

The storm is expected to bring a lot of rain that could cause dangerous flash floods and potential mudslides. About 8 inches of rain is expected, basically a year’s worth of rain in 36 hours.

The last time a tropical storm made landfall in Southern California was in 1939, 84 years ago.

While NOAA predicts the storm will begin weakening by late Friday, its two potential paths remain the same for now. 

The first one is tracking along Baja California, where the rugged mountain terrain might tear it apart. Then it could head into Southern California and continue northward, affecting areas like San Diego, Palm Springs, Las Vegas and Reno.

The second path shows Hilary remaining offshore, skirting along the coast as a tropical storm, causing heavy rainfall from San Diego to Malibu. This is what could trigger widespread flash flooding and potential mudslides.

SEE MORE: Study: Significantly more US hurricane-related deaths among vulnerable

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