King Tides don’t always follow the tide tables

UPDATE: Dec. 19

An app used for reporting King Tides can also be used to report marine debris along the shoreline. Check out the news release issued today by the Washington Department of Natural Resources.
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Higher-than-predicted marine waters, brought about in part by recent weather conditions, have given us unexpected “King Tides” in many areas of Puget Sound.

I noticed that the waters of Hood Canal seemed exceedingly high this afternoon, as I drove along Seabeck Highway where the road hugs the shoreline. The waters were not supposed to be this high, according to tide tables developed by the National Oceanic and Atmospheric Administration, so I checked some actual levels recorded at nearby locations.

High-water levels measured on the waterfronts in Seattle, Tacoma and Port Townsend were nearly 1½ feet higher than what had been predicted by NOAA for those areas. For example, in Seattle the preliminary high-water level was listed at a tidal elevation of 12.98 feet at 12:54 p.m. today, compared to a predicted high tide of 11.56 feet.

This is the season for King Tides, a name given to the highest tides of the year. High tides, mostly generated by the alignment of the sun and the moon, are predicted for Christmas Eve, rising higher to the day after Christmas and then declining. But, as we’ve seen this week, as well as on Thanksgiving Day, predicted high tides can be dramatically boosted by heavy rains, low atmospheric pressure and onshore winds.

As one can see by looking at observed and predicted tidal levels in Seattle, the actual tidal level has exceeded the predicted level more often than not over the past 30 days — and lately it has been higher by quite a lot (shown in chart at bottom of this page). Actual levels are measured in real time in only 14 places in Washington state. One can access the charts from NOAA’s Water Levels — Stations Selections page.

King Tides are promoted as an event by Washington Sea Grant and the Washington Department of Ecology, because today’s extreme tides provide a reference point for sea-level rise caused by climate change. The highest tides of today will be seen more often in the future, and even higher tides are coming. Check out the blog post on Water Ways from Jan. 3 of this year. See also the website “Washington King Tides Program.”

Washington Sea Grant has posted a list of dates when high tides are expected in various areas, called King Tides Calendar. Sharing photos of high tides hitting the shoreline is part of the adventure, so sign up for MyCoast to share your pictures or view images posted by others, or download the cellphone app to make the connection even easier.

The chart shows the actual tidal water levels in Seattle (red) compared to the predicted levels (blue). Click to go to NOAA’s website.
Chart: NOAA

2 thoughts on “King Tides don’t always follow the tide tables

  1. The red line is never lower than the blue line in the chart, indicating that actual tide levels were always higher than predicted tide levels.

    Atmospheric pressure is the primary cause of deviation, causing as much as 2+ feet higher or lower than the predicted levels, which are based on average conditions.

    This chart would therefore indicate that atmospheric pressure was lower than average throughout the period. Was that true?

  2. UPDATE: Dec. 19

    An app used for reporting King Tides can also be used to report marine debris along the shoreline. Check out the news release issued by the Washington Department of Natural Resources.

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