Water rises over the banks of Finn Creek during a king tide, Dec. 17, 2012. (flickr photo, user kjshawcroft)
Last month, the so-called "king tides" lead to coastal flooding along the West Coast of the U.S., in particular.
According to a story in the West Seattle blog, preliminary data indicates the storm tide from Colman Dock in Downtown Seattle on Dec. 17 set an all-time record, there, topping a record from January 27, 1983. Records at Colman Dock date to 1898.
In California, water seeped into cars at a commuter parking lot in the Bay Area suburb of Marin City and flooded part of the Pacific Coast Highway in Sunset Beach. Residents in Newport Beach tried to keep ankle-deep seawater from inundating their homes and businesses.
More king tides are expected starting Thursday. Let's delve into a little "Science 101" and demystify the tides deserving of a royal name.
(COASTAL FLOOD ALERTS: California)
The king tides are caused by the lining up of the sun, moon, and Earth while the moon and sun are relatively close.
King Tides: The Year's Largest
The Earth's tides are caused by the gravitational pull of primarily the moon, but also the sun on the Earth's oceans, as well as the Earth's own rotation.
During the times of the new and full moon, twice every 29.5 days, the sun, Earth, and moon are oriented in nearly a straight line, an alignment known as "syzygy" (the best Scrabble word I've ever seen).
At these times, the sun's gravitational pull works together with that of the moon, creating higher high tides and lower low tides. These are called "spring tides," not named according to season, but due to fact the tide amplitudes "spring up and down."
But these aren't the "king tides."
The Earth's orbit around the sun and the moon's orbit around Earth aren't perfect circles, but rather ellipses. This means there's a point in the orbit at which the moon is closest to Earth ("perigee") and one at which the Earth is closest to the sun ("perihelion").
Each month, the moon's distance from Earth varies from around 226,000 miles away at perigee (its closest point) to 252,000 miles away at apogee (its farthest point).
Perihelion just occurred on January 2, 2013. At that time, the Earth was 91.4 million miles from the sun, or about 3-4 percent closer than its average distance of 93 million miles.
Summarizing, the king tides result from the additive effect of ...
- Syzygy (alignment of sun, moon, and Earth)
- Perigee (closest approach of moon to Earth)
- "Almost perihelion" (Earth almost as close at it gets to the sun in its orbit)
Occurring only a few times a year, king tides are the highest of the high tides each year.
If a major storm coincides with the king tides, such as a Pacific storm sweeping into the West Coast, battering waves and high surf can ride atop the effects from the king tides. Remember, Superstorm Sandy occurred during high tide.
Fortunately, we don't see any major storms targeting either coast through early next week, although a couple of Pacific frontal systems will sweep into the Pacific Northwest late Tuesday/early Wednesday, and again next weekend.
This also raises concern in an era of rising sea levels during climate change.
Initiatives in several coastal states, including the California King Tides Initiative, is encouraging the public to submit photos of the coastal flooding to raise awareness.
(SUBMIT YOUR PHOTOS: iWitnessWeather)
MORE ON WEATHER.COM: TSUNAMI DEBRIS
In this file photo from Wednesday, June 6, 2012, a man looks at a 70-foot-long dock with Japanese lettering that washed ashore on Agate Beach in Newport, Ore. The West Coast is anticipating more debris from the 2011 Japanese tsunami to wash ashore this winter. (AP Photo/Rick Bowmer, File)