California's highest tides of the season, the so-called King Tides, will be in full force this week.
These huge tides come only twice a year, causing Pacific Ocean waves to surge onto the beaches.
King Tides occur when the gravitational forces of the sun, Earth and moon are aligned. High tide is expected to peak today (Feb. 17), and it comes at a bad time: just as a storm is moving toward the West Coast, which could produce flooding.
"Normally, a King Tide will cause some beach erosion because some tides are higher up on the beach. But what we have this time is a combination of the King Tide and large swell," said Steve Anderson, a forecaster with the National Weather Service's San Francisco Bay Area office.
Tides are already surging up to 6.3 feet (2 meters), Anderson said. Along with heavy rain today, the swell could bring waves up to 15 feet (5 meters) throughout the day. The huge waves and King Tide could combine forces and push water over the seawall in some places, causing floods, Anderson told OurAmazingPlanet.
The term "King Tide" can refer to a particularly high tide anywhere. When the sun and moon are closest to the Earth and in line, King Tides swell onto the shore.
When the moon is closest to the Earth called perigee its gravitational pull is the greatest. The moon has more influence on the tides than the sun does, but the sun plays a key role to create King Tides. When the sun is closest to the Earth called perihelion it, too, exerts its peak gravitational pull on the Earth. So when the sun, moon and Earth line up at perigee and perihelion, which happens twice each year, the gravitational force on the Earth is strongest, creating the huge tides.