Gray water, rippling with rainfall, lapped at the banked edge of the Coyote Point waterfront at the San Francisco Bay, covering the high-water mark – a line of white bricks – by at least a foot.

Nature gave a preview Nov. 24 of what's coming to San Mateo County with sea-level rise. King tides occur when the sun and moon align their gravitational forces when the ocean's tide is at its highest.

At a "King Tides and Coffee" presentation given at Coyote Point park in San Mateo, hosted by San Mateo County's sustainability office, a group of about 20 people, including county supervisor Dave Pine, witnessed just how high that water could get.

According to Hilary Papendick, a county climate resiliency specialist, several factors are contributing to current high water levels.

The king tides are one factor, she said, but another is the warmer water that El Nino conditions bring. Water expands when it is warmer, she said, which alone could cause a further 6 to 10 inch increase in water levels this winter. The latest measurements, she said, show that the water this winter is the warmest on record, surpassing 1998 El Nino temperatures. Ms. Papendick presented images from the 1998 El Nino season, showing streets rendered impassable due to flooding.

Ms. Papendick said that the best estimates predict a sea-level rise of 2 to 12 inches by 2030, 5 to 24 inches by 2050, and 17 to 66 inches by 2100 across California, according to a report by the National Research Council.

Across the county, she said, higher water means that communities built along ocean bluffs risk erosion, wetlands and estuaries risk saltwater encroachment, and bayfront and oceanfront businesses risk massive economic loss due to flooding.

To ascertain the extent of that risk, she and her colleagues are conducting a vulnerability assessment, a year-long study expected to be finished in June 2016 and that evaluates the county's assets at risk.

Climate resiliency assistant TJ Carter said people need to know that "San Mateo County is the most vulnerable county in California" to sea-level rise. According to a 2009 study by the Pacific Institute, that county-wide vulnerability equates to about $24 billion in assets at risk from sea-level rise.

After the vulnerability assessment is conducted, the county will take measures to prepare for and mitigate the impact of sea-level rise, Ms. Papendick said.

King tides can also be viewed Dec. 22, 23 and 24, and on Jan. 21 and 22.

Check saltwatertides.com to see when the high tide will peak.

Coastal locals are also invited to submit photos of the king tide peak to the California King Tides Project. Caution is advised.

Click here for more information.