The Rise of King Tide: What it is and Why It’s A Big Deal

Norfolk neighborhood is inundated by a king tide/ Credit: The Virginian-Pilot

For most people, December means it’s the holidays. It’s a time that is spent either shopping, eating, or simply being with family. However, this time of year means something else for those in low-lying areas along the US coastlines. It means king tide.

Before diving into how king tide affected West coast residents just this past December, it is important to understand what king tides are and how they differ from normal tides. The semi-annual tide, also known as the perigean spring tide, occurs when the Moon’s perigee (the point when it is closest to earth in its orbit) coincides with the alignment of the Moon, Sun, and Earth. Being semi-annual, it usually occurs once in the summer and once in the winter, with the most recent one being right around Christmas of 2018. It is the highest high tide of the year for most coastal locations.  Given the high predictability of king tides, meteorologists are often able to issue the necessary flood warnings well in advance.
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The most important takeaway though, when it comes to king tides, is that they are not caused by climate change. King tides occur on a perennial basis, always at roughly the same time of year, and have occurred throughout human history. However, king tides are reaching areas farther inland than they have previously, and this factor may very well be because of the melting of freshwater and mountain glaciers, which are causing sea levels to rise. Factor in warming seas, which are causing thermal expansion (heat expands, so warmer oceans will rise more), and you have worsening king tides. It’s something that was noted in the Bay Area just this past December, when warmer-than-normal water temperatures in the Pacific Ocean along the coast may have caused ocean waters to crest several inches above tidal gauges. The average temperatures for the Pacific in Northern California in December are around 55 degrees Fahrenheit; this December, the Pacific averaged in the upper-50s, with parts of Monterey Bay edging the 60 degree mark.
 
While the West coast saw the most recent king tides, it’s the low-lying East and Gulf Coasts that are seeing the most severe flooding from king tides. An official with the Environmental Protection Agency, whose hometown is among those affected by extreme king tides, attempted to document the increase in king tide flooding through a blog post back in 2013. He found inland areas of the town were flooding more frequently, and this was especially prevalent in the aftermath of Hurricane Sandy. This area is now situated in Federal Emergency Management Agency’s highest flood zone category.
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Further down the coast, in Virginia’s Hampton Roads region, residents have been feeling the effects of king tide flooding for years. In fact, king tide flooding often occurs on normal, fair weather days, leading them to be colloquially known as “sunny day” tides. This has been detrimental to local infrastructure, travel, and even the economy. Local officials are often forced to close roads and divert traffic away from the coast as a safety precaution. It’s something that isn’t new, says Jeff Orrock, the Meteorologist-in-Charge at the local National Weather Service office in Wakefield. “In general, sea level rise across Hampton Roads has been rising at a rate of 4 to 6 millimeters per year”, said Orrock. He indicated this was an average, and that there have often been periods of higher sea level rise, ultimately causing king tides to become more noteworthy. “King tides are more of an issue and we reach nuisance flooding on a much more frequent basis now than just 10 to 20 years ago. We even issue more flood advisories and warnings than just 10 to 20 years ago.”

Ten years ago isn’t a long time, but it has given some coastal residents time to prepare and organize local, and even statewide movements. Oregon residents have joined forces with the international King Tide Project, an Australian-founded initiative that motivates everyday citizens to document their local king tide, post it online and share it for others to see. The movement was founded in order to provide people with an idea of what type of tidal flooding will be normal in the future, should sea level rise and other climate change phenomenon continue at their current pace. In the meantime, residents along the U.S. West coast are preparing for two more king tides, one around January 21st and another in February, both predicted to be more than a whopping ten feet. 

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© 2018 Weather Forecaster Jacob Dolinger