Factor 1: Celestial Bodies
There was a full moon during the highest king tides, but on top of that, the sun, moon and Earth were all aligned and in close proximity to each other. This formation created extra pull on our tides here on planet Earth.
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Factor 2: Low Pressure System
While this celestial formation was happening, there was also an area of low pressure crossing Northern California. This also created storm surge on our bay waters.
The perfect timing of the combination of the extra gravitational pull from our moon and the storm surge from low pressure created record tidal flooding we have not seen since 1998 in the Bay Area.