A Tolkien tide
Having been a fan of Tolkien’s faerie tales since I was chasing
squirrels in the oaks and hickories of the heartland, it’s no
surprise I’m excited to see the Hobbit. My dear Alejandra even
bought me a ticket to the opening show at our local theater. Of
course, that requires staying awake!
If you too have any intention staying up for a midnight cinematic premier, mother nature will provide a premier low tide (-3.6’ish) to fill the “I really should be going to bed now” hours with “Ooo’s” and “Ahh’s” in the beam of your light. For most of the inland Salish Sea, the tide will be in minus territory any time after 9:pm and bottoms out around around 11:pm. It’ll probably be wet and chilly, so dress well and feel free to share what cool things you see through comments or by contacting me directly.
Swollen seas
‘Tis the season for storm surges.
The week before Thanksgiving, I saw the 12’ predicted high tide lapping on the beach as I walked off a ferry to West Seattle. A stream babbled north under the dock, well above the tide and buffered by large wood and another few feet of gravel/sand beach.
I traveled the same path a week later, when the predicted high tide was actually a few inches lower. However, the storm tide had swamped the beach logs and stream both, lapping in the vegetation of the recently restored shoreline. Numerous logs with cut ends had rolled and floated out into the bay – an example of the sub-par services cut logs provide when compared to their rooted and branched brethren.
You may also recall the heavy rain before Thanksgiving. Along with that came the surge that I observed and that you can see in the graph below. The actual water levels (red) pushed almost 2 feet higher than the predicted level (blue). The green shows the difference between the two. When predictions hold, the green line stays on zero.
Heaping on the water
Tides are predicted based primarily on the locations of the Earth,
Moon and Sun. Those astronomical or predicted tides are the numbers
we see in our tide tables, apps or calendars. We have a great deal
of certainty as to where the heavenly bodies will be at any given
time in the future, but back on our corner of the blue planet,
long-range weather details are largely unknown. Consequently, we
have no long-range ability to factor storm surges into our tidal
predictions.
Storms, caused by the collision of colder northern air and warmer southern air, set our Pacific waters in motion. The warm air rises, lowering the pressure the atmosphere applies to the ocean and allowing the ocean to swell. That pressure-driven surge is accompanied by some level of wind-driven surge, as the rising warm air also fosters stronger winds that pile the water up on the coastline.
Since our region is spared tropical cyclones (we seem satisfied with earthquakes and volcanoes), our storm surges are mild compared to what everyone watched the East Coast suffer during Hurricane Sandy (right). Still, it’s not unusual for our waters to surge 1 or 2 feet higher than expected during stormy seas.
Our strongest storms often strike in the winter, when we also have some of our highest predicted tides (see and be part of WA DOE’s King Tide photo initiative). Add 20 inches of storm surge to an already high tide, then throw in some high wind and waves… repairs to shoreline properties, roads, and utilities often follow. Factor in potential effects of climate change (a few inches of sea level rise, more intense storms), and the issue of storm surge becomes an important consideration with regards to shoreline infrastructure. Oh, and that kayak that you didn’t bother to tie up because it was 2 vertical feet above the highest predicted tide… (ouch!)
Tide fun courtesy of NOAA
If you enjoy exploring graphs and numbers, you can have some fun
through NOAA’s Tides & Currents portal. You can even check out
sea level changes over time and historical extremes. The “Seattle,
Puget Sound” station’s highest recorded water level was in January
1983 at +14.48 (right). Not too bad considering our recent big
surges were about +14. Certainly nothing compared to the extra 10
feet piled onto the east coast shorelines.
When you’re playing with the numbers and graphs, remember the -8hr conversion from GMT and a -7.94 feet conversion from the extremes section to make them comparable to what we’re used to seeing (based on mean lower low water [MLLW] as 0.0, instead of the station standard that’s 7.94 feet below MLLW).
Have fun exploring NOAA’s online tidal treasures and our last lowest tide of the year! And if you fall asleep at work or school tomorrow… you didn’t read this.
Jeff Adams is a Washington Sea Grant Marine Water Quality Specialist, affiliated with the University of Washington’s College of the Environment, and based in Bremerton. You can follow his Sea Life blog, SalishSeaLife tweets, FaceBook and video posts, send email to jaws@uw.edu or call at 360-337-4619.
