King Tides and Minus Tides

     High and low tides are a fundamental part of life in the San Juan Islands and beyond. 

They occur in a predictable pattern, much like night follows day. However, a few times each year, the alignment of the sun and moon causes extreme tidal conditions known as king tides and minus tides.

     As the names suggest, these tides are significantly higher or lower than normal. 

When we study a NOAA tide forecast for a specific location, we typically see times and heights such as 7.5 feet at 9:04 am, followed by a low tide of 2.5 feet at 3:02 pm, approximately six hours later. By doing some simple math, we can see that the tide will fall (range) five feet between high and low tide. This is our usual scenario, although the times shift by about fifty-four minutes later each day.

     However, as the sun and moon's positions approach perfect alignment, the tides become more pronounced, resulting in king tides and minus tides.

 For instance, a high tide might reach +10.5 feet, while a low tide might drop to -3 feet, creating a nearly 14-foot range over a six-hour period. These figures are not hypothetical; they were taken directly from the NOAA website for Fisherman Bay

Minus tide in July at Jones Island leaves an unwary runabout high and dry delaying departure.

     For a cruiser in the San Juans, considering where and how you anchor or tie to a float becomes even more important during these extreme tides.

 Your favorite dock might be sitting in the weeds at low tide, or your anchor rode might be too short at high tide. Careful planning of your passage becomes crucial. A pass or headland you routinely transit might have five-foot or higher standing waves and an eight+ mph current during these times.

      Familiarizing yourself with the "rule of twelfths"

rule of twelfth's is a useful way to prepare for and estimate water levels at your chosen anchorage. Knowing the depth in advance won't make your boat any faster, but it could help you adjust your plans to avoid the worst of the conditions.

     All cruising requires vigilance and preparation but during king and minus tides, a little extra knowledge will assure you have a safe passage.

Click below for a satellite view of Jones Island