I never wait for the federal government to tell me when its a good time to leave.
Also consider when was the last tropical storm to hit SoCal? I was in Hurricane Gloria that made it to New England. that area hadn't been hit by a real cyclonic storm in ages. It was a bloody mess, no power for near a week, can't travel as all the roads have trees across them, etc.
The the same will happen there is its even a moderate tropical storm. Then if FEMA tells you to evac there won't be a viable route out. So like Gloria you are stuck in place in a desert climate in late summer.
Go to Scottsdale, have a mini vacation. If its a big nothing burger then you got nice few days out of LA. If it ends up a shit show you dodged a bullet w/ a nice few day w/o dealing w/ any of it.