About the Class

The movement of water around the Salish Sea and Planet Earth has fascinated people for as long as we have been around. Why does it do that? How do we predict where it will be in an hour, a day, a year from now?

How does all this affect the locations of salmon, seaweed, and nuclear power plants? And how does all this affect me when I visit the beach, paddle a kayak, take a ferry, or try to balance an egg?

Tides wait for no man, but that means they are predictable. How does a storm change those predictions? Should we use the dependability and energy of tides for power generation?

Using video, diagrams, discussions, and humor, this hour-long interactive presentation challenges assumptions, offers insights, and helps us understand the science behind what is taking place out in space and along our shores every hour of every day, processes that create our tides, determine our coastline, and touch our lives.

Follow-up session questions and answers:

Do low-low ever precede high=highs, or do they always follow?
It depends. Sometimes they precede, sometimes they follow.

What does amphrodomic (sp?) mean? Amphidromic!
Amphi means around, dromos is running, so it literally means 'running around', which is what the tide does at these points, going around them in circles. Tidal node is another term you might see.

What is a mean high tide?
Mean basically means average, almost. So the average high tide would be mean high tide.

Also, how does the feet of a tide get measured? From what point is a 9" tide measured.
Zero is determined by the mean lower low tide, in America, so the average of all the lower low tides. That is the baseline from which all other tides are determined for height.

We are boaters and I find we often miscalculate slack tide in important areas with lots of currents like Malibou Rapids in BC - using a rough estimate of an hour before a time change - what is the best way to figure out slack tide?
By using a current chart. Slack tide in one place might not be a slack current, which does not sound logical, but the current can start flowing before the water on one side of a pass has fully come up or down. Tide charts show the height, and technically slack occurs at the point between ebb and flow, but the nearby channel might be a different story.

Where can easily find the dates/times of expected King tides on central Whidbey Island (Greenbank?) for the next several months? I would like to correlate these with expected higher north winds.
Great project. Check out your tide chart, and see what the highest tide line is, and look for any tides that are at that height. Then watch for low pressure systems, onshore winds, and heavy rain to make it even higher, a king tide.

So 'zero' tide level is not average sea level but average low?
Yes, exactly right, well almost, the average lower low tide, not the average low. And the mean, not the average, but now we're getting into the weeds.

How often are the tidal baselines reset?
Every 19 years, and we just entered the newest one.

Can you explain why the tides around vashon only go one way?
Good one! You made me do some research. Deep Zoom is where I start to watch the currents in action for various tides. I watched a few days' worth of tidal movement, and saw that Colvos Passage on the west has ebb tides that are up to a knot and a half or more, maybe 2 or more, but that the flood tide through there is just a couple tenths of a knot. Curious! So I looked at the geography, the landforms. Check out the direction a flood tide would take - from Admiralty Inlet into Seattle it would take the main channel, and keep going down the east side of Vashon where the channel is wide and open to the north. Colvos passage is narrow and doesn't get much of that. But on the ebb, the heavy current out of the Tacoma Narrows heads right into Colvos, feeding that channel every ebb tide. So I believe that causes the Colvos Passage tides to be strong on the ebb, and weak to non-existent on the flood. The east side is the opposite, though not as pronounced. How's that?! Tides are amazing.

Are there always two high and two lows in 24hrs?
Usually, here. Not everywhere, but much of the world, and sometimes only 3.

What are sneaker waves caused by? And have you seen/heard of any in the Salish Sea?
Waves are a whole different story! These can be generated by wind, earth movement, and other factors. Sneaker waves can be caused by a variety of factors too.

Would you recommend any resources to learn more about the tides in this area?
There are very few specific to this area, except those buried in masters theses. But there are some. The UW Oceanography department is a key resource for us.

Is a riptide really a tide, and if so, how.
Riptide is a generic term covering a few different actions, usually a combination of wind and waves and currents interacting to create an anomaly, something unexpected for the direction of the water. It is dependent on the landform of the beach, the weather, and the currents. Sometimes normal tidal current action is called a riptide, but there are specific places that get quite interesting movement that are strange to believe until you see them in action.

Is there a current app that you recommend?
I use "Tides". Plain and simple and quick There is also NauTides with lots of details. And a bunch of others. Check out your app store and see what you like.

Low low tide precedes high high tide on Feb 15 & 16
And on the 18th it the higher high tide precedes the lower low. It goes back and forth from time to time.

What are some simple rules to plan a kayak trip, for example, from Anacortes to Cyprus island?
Go there from Washington Park on a flood tide, come back on an ebb! Those are as simple as I can make it, but launch points, weather, the range of tidal change, and so much more affect all that.


His University of Washington senior thesis explored the management of Washington State Park's Puget Sound beaches. Somehow he graduated from college with a B. S. degree in Forest Science, specializing in park management. He spent the next forty years working in nine different Washington State Parks. Deception Pass was Jack's last state park to call home, living there for fourteen years, and performing numerous rescues and recoveries in the churning waters of the Pass. He retired in 2017 and now makes his home in Skagit County.

He loves beaches, sunsets and sunrises, warm weather, flying, photography, hiking, sauntering, kayaking, biking, laughing, basketball, writing, playing with his kids and grandkids, eating blackberry pie, and finding rainbows.

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