The mountains are what normally prevent the coast from seeing any of the monsoonal storms typical of CA/AZ deserts in mid-summer. It's common for moisture coming from Mexico to produce large thunderstorms east of the coastal mountain ranges this time of year.
I'm not saying this storm won't amount to anything for the coast. We'll probably get some rain and some wind. I'm not stockpiling anything and my only prep has been to put a bit of gas in the car and charge all of my batteries. We're most likely going to roll our eyes at the people panic-buying TP and water this Monday.
Edit: It's 12:32 AM in San Diego. According to several online radar maps including weather.com, we've been in the middle of a rainstorm for almost an hour. The ground is still dry and it's a calm 73F outside. Very weird. I can understand radar picking up light rain which evaporates before hitting the ground, but the map is indicating rain that is much heavier than that. Weird.