"El Niño, California Precipitation, and Landslides" <https://www.conservation.ca.gov/cgs/landslides/el-nino>

El Niño is the “warm phase” of the El Niño-Southern Oscillation and features warmer than average ocean surface temperatures off the coast of Ecuador and Peru in the equatorial eastern Pacific Ocean.... Historically, the presence of El Niño conditions tilts the odds in favor of wetter than normal precipitation across the southern third of the state. The relationship between El Niño and cool season precipitation is weaker in the central and northern parts of the state.

Flooding is possible, particularly if dams exceed capacity, perhaps exacerbated by earlier snowmelt and peak runoff. Landslides are a more widespread, and less manageable problem, particularly as loose-material slopes are waterlogged. The deluge -> high growth -> heavy fuel load -> large wildfire -> landslide cycle is one that's become fairly well-known in California.

Levee failures within the Sacramento Delta or Central Valley could result in very large-scale flooding, affecting agriculture or communities.

The San Francisco Bay Area may see "king tides" and general flooding throughout the bay and delta region, particularly during December and January, and all the more so if high tides coincide with heavy river run-off. Remember that the entire Central Valley of California, nearly 500 miles long north-to-south, drains out through the Bay. Prevailing winds may create a wind setup or seiche which can result in flooding along a some but not all shorelines, or alternating across a body of water.

<https://en.wikipedia.org/wiki/Wind_setup>

<https://en.wikipedia.org/wiki/Seiche>

Yes, atmospheric rivers all winter.

Next year a super bloom then the following year massive wild fires.

rain -> fuel -> fire

Most of the most flood prone areas in CA have been significantly neutered over the decades thanks to massive water projects. There was a time when the LA river would destroy LA routinely. Now everything is channelized. At risk communities are probably the handful of remote ones that do not have great infrastructure, but I'm not even sure where those might be given how the state seems to be able to build thousands of debris flow cement storm drain setups in relevant areas.

Other states seem a lot worse off. Water table is closer to where people live, there's a lack of topology to actually run water out in a lot of cases, there's been little investment in managing water for stormwater for property damage abatement or power or irrigation like in CA where the topology really incentivized massive investment in all of that over the last century.

We haven't had any significant flooding in past El Niños. Of course, it will probably be different this round, but at least El Niños tend to align with Mediterranean weather instead of droughts and wildfires.

We also have one of the more advanced waterwork system in the US to support Central Valley agriculture, so a lot of the worst aspects can be somewhat managed.

It's bad that such dramatic climate change is happening, but we're definetly lucky to live in the West Coast because we won't face the brunt of some of the worst aspects of the El Niño comparatively and have the infrastructure to deal with it.

Sadly, the brunt of climate change will be felt by the poorer half of the world.