Weather Blog

What are 'king tides' and why do they occur in winter?

What are 'king tides' and why do they occur in winter?
Tis the season for "king tides" -- a name given to unusually high tides that occur in the winter time around the full moon.

Typically, times of full moon enhance the tides every month because the sun and moon are in alignment, enhancing their gravitational effects on the tides.

But in the winter -- usually peaking in January -- the high tides get a little extra oomph due to the fact that the Earth is at its closest point to the sun in its elliptical orbit.

"Perihelion" usually occurs around January 4th or 5th and if we ever see the sun in Seattle in January, you'd notice it's about 5% larger than it is in July.

Anyway, being closer to the sun means the sun exerts a little more gravitational pull on the tides and thus you get higher tides this time of year. Here is a chart of the king tides for late January and late February in Western Washington.

The higher tides can cause some minor flooding around large bodies of water that can be exacerbated by stormy weather at the time. (For this year, it looks like the late January tides will be mitigated by expected calm weather during the period.)

If it happens near you, the Department of Ecology is asking for people to upload photos of the flooding so they can get a better understanding of how eventual rises in sea levels could affect local area.

You can find more technical information about spring tides and king tides at NOAA's website.

Is A Closer Sun the Reason for a Warm Winter?

(I meant to post this around Jan. 4 and forgot, but it ties into the king tide, so -- it's my excuse for running this now:)

La Nina is missing in action, and January is warm again for the second year in a row. Could it be the fact that we're closer to the sun?

No, but nice try.

Around this time of year, we are about 3 million miles closer to the sun than we will be around the 4th of July, when we're at "aphelion". (No correlation on whether the smaller sun is the responsible for the fact that July 4 is statistically the wettest day of July. That's just Seattle working its ironic weather magic.)

The next question you might ask is -- does that mean our summers are cooler then the southern Hemisphere, since they are closer to the sun in their summer? And our winters are warmer since the sun is closer?

The logic is sound, but in actuality, it turns that it's not the case.

The Earth does receive 7% more energy from the sun in January than July, but most of the Earth's land is concentrated in the Northern Hemisphere.

Land does a much better job than ocean of absorbing and releasing the sun's energy -- i.e., ground heats up faster and more easily than water.

Thus, even though we get less of the sun's energy in the summer, we have more land in the Northern Hemisphere summer to where the sun's energy heats up more. So much so that the Earth is actually, on a whole, about 4 degrees warmer in July than January, even though there's less energy.

(Note that the Earth's tilt on its axis is way more influential to the seasons and global temperature than the minor change in the distance from the sun.)

Another trick -- the Earth's orbit speed is slightly faster this time of year as when the Earth is farthest away from the sun. That means virtually speaking, our summer ends up being about 3 days longer than the Southern Hemisphere summer/Northern Hemisphere winter.

Of course, around here, you might be hard pressed to convince people that summer is three days longer than winter!