Large flooding is very hard to predict. Sometimes it will flood every year and other times it won't flood for forty years. This irregularity is caused by San Diego's climate. Normally, high-pressure areas over the ocean cause northerly coastal winds that keep the California Current cold. This stabilizes the high-pressure region off the coast of San Diego.
High pressure means falling air, which is a condition minimizing cloud formation.
If clouds can't form, then it will not rain. Winter storms and tropical storms now readily invade the coast causing abnormal amounts of rain. The name refers to the Christ Child of the Christian faith. This allows the colder subsurface waters that are rich with nutrients to move to the surface. The nutrients, now at the surface, stimulate the growth of phytoplankton.