Perigee

Tides: A Deep Dive

Part 4

We’ve covered that tides have diurnal and monthly characteristics. Now onto the third category.

Some characteristics of tides happen on a basis that is something between monthly and yearly. I’ll try to explain. Each trip of Earth around the sun (we call this a year) contains about thirteen lunar cycles (aka months), each of which are twenty-seven and one-third days in duration. During each of these thirteen trips of the moon and Earth around each other, the moon is closer to Earth at one point each month. This state is called perigee.

Perigee is a consequence of moon’s orbit being elliptical. Apogee is its opposite, when the moon is farthest from Earth. Perigee produces even more extreme diurnal tides on the days it occurs. Twice-ish per year, the timing of this close approach of the moon to Earth coincides with lunar spring tide on the new or full moon, and the effects are additive. The spring tides are of even greater magnitude than their normal monthly basis. This correspondence of perigee with syzygy only happens certain months in a given year.

We can call this perigee syzygy, okay? (This is not what people call it but I do think it would make sense.)

The internet told me that perigean spring tides occur “about three or four times per year, in spring and fall” but I dissected what this means. In spring and fall, the syzygy-perigee phenomena are most likely to overlap each other in time, so the best bets for Perigee tides are around March and October. Sometimes we get an extra one or two of these perigee-syzygy events in, say, April, or September.

This spring, a new moon (syzygy) will take place on March 29, with perigee occurring on March 30. A nice few days of especially negative low tides will happen March 31 through April 2 as these combined forces play themselves out. (This is my tidepooling-centrism speaking; there will also be some very high high tides those days, but for me that’s an afterthought.) In both April and May, new moon and perigee co-occur on the same days! April 27 and May 26 feature low tides of -2 feet or better. These will be some of the best tidepool times for me this year, as they occur in the morning hours.

In the fall, both October and November have some perigee-syzygy tides! Unlike the spring 2025 ones, these will co-occur with full moon instead of new moon. October 6 full moon rests near the October 8 perigee. November 5 is both full moon and perigee, resulting not only in extreme tides, but also in a supermoon! December, too, will have a full moon/perigee/supermoon on December 5^th.

Originally (in 2020 when my I began this research) I surmised that we probably have perigee-syzygy a minimum of twice per year, and could have it up to four times, with two of them having possibly slightly decreased magnitude based on how well synchronized the perigee and syzygy are. But it seems to me that this upcoming year is extra bountiful with perigee-syzygy tides… six!

In 2020, I found perigee-syzygy events in March and April, September and October, for a total of four. Another fascinating tidbit is that 2020’s spring perigees were closer to full moons, and fall perigees closer to new moons, whereas we are flip-flopped in 2025.

I’m kind of blown away with how much more there always is to learn about this process. And who knew that some years could be better for tidepooling than others? I think I have a lot of ideal tidepooling conditions in store for me this year!

Next week, more on the sun.