Conditions Aligning for Bay Area to Expect Highest King Tides in 18 Years

The San Francisco Bay Area gets coastal flooding from King Tides every winter, but this year could be different. Scientists say the region may see its highest tides in 18 years this fall and winter. Several forces are lining up at the same time to push water levels unusually high. It is not just one cause — it is a combination of the moon, the sun, warmer oceans, and climate change all working together.

Tides are caused by the gravitational pull of the sun and moon on Earth. In early January, Earth is at its closest point to the sun in its yearly orbit. That means the sun's pull on our oceans is a little stronger than usual during the winter months. When the Earth, sun, and moon line up during a full or new moon, tides are also a bit higher than normal.

About once every 28 days, the moon reaches its closest point to Earth, called the perigee. At this point, the moon's gravitational pull is at its strongest. When a new or full moon happens in winter — with the moon near Earth and Earth near the sun — it creates the highest tides of the year. These extra-high tides are called King Tides, and the Bay Area experiences them every single year.

There is also a slow wobble in the way the moon tilts as it orbits Earth. This wobble follows a cycle that lasts about 18.6 years. During the first half of the cycle, tides are stretched — meaning high tides get higher and low tides get lower. Right now, we are in that first half, which means high tides are even higher than they would normally be.

On top of all that, there is a very strong El Niño this year. El Niño is a weather pattern caused by warmer-than-usual water in the Pacific Ocean. Warmer water actually expands and takes up more space, a process called thermal expansion. This means that even without any storms, the ocean surface sits a little higher than it would in a cooler year.

Sea levels have also risen due to climate change over the past century. Baseline sea levels in the Bay Area are at least 8 inches higher than they used to be, and that extra height adds to the already elevated tides. All of these factors together create the conditions for some very high water this winter.

The highest tide ever recorded in San Francisco measured 8 feet and happened on January 27, 1983. The original forecast for that day was only 6.8 feet, but a 2-foot storm surge pushed the water to record heights. This December, King Tides are predicted to reach 7.33 feet — already higher than the 1983 forecast. If a storm adds another 2 feet of surge on top of that, the all-time record could be broken.