April Supermoon 2021: Expect Higher Tides as Lunar Cycle Shows Effects of Sea Level Rise

There is something more going on in the moon's orbit around the Earth that people should be mindful of. Experts said this week's supermoons could cause bigger tidal ranges, higher water levels.

Forbes said growing tides triggered by last month's supermoon allowed rescuers to free the Ever Given container ship stuck in the Suez Canal just last month.

(Photo: pixabay)

A "supermoon" is a full moon that tends to be much heavier than a regular full moon. Astronomers refer to these full Moons as perigee full Moons.

Since the moon's orbital path around Earth is a minor ellipse, there is a near-point (perigee) and a far point (apogee) each month (apogee). At perigee, it appears slightly larger (a "supermoon"), and at apogee, it appears slightly smaller (a "micro moon").

April's Full Moon, the second of four "supermoons" or "perigee full Moons" in 2021, will be around 6% heavier than an average full Moon.

What the Moon Has to Do With Coastal Flooding

The magnetic force of the moon is the primary cause of tides on Earth. The ocean is continuously sloshing as Earth revolves behind the moon once a day and the moon orbiting Earth once a month.

US NOAA explained that the moon's gravitational force causes a bulge in the ocean water nearest to it, to put it simply. Thanks to the inertia of the sea, there is a bulge on the opposite side of the Earth. NOAA also explained that high tides occur every 12 hours and 25 minutes in each coastal region as the Earth rotates around these bulges. Based on where you are, some tides are higher than others.

The sun also impacts the Earth's rotation and elliptic orbit around the sun cause tides to change during the day and year. However, this contribution is smaller than half of what the moon makes.

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Though it has been occurring for nearly four billion years, this gravitational tug-of-war on our water was only discovered nearly 450 years ago. In short, the moon has a major influence on how we perceive sea level. While it has little effect on the sea-level increase, it may mask or exaggerate it.

How the Moon's Orbit Affects Sea Level

The ecliptic plane is the plane in which the Earth orbits the sun. For the sake of convenience, let's pretend that the plane is level. Consider the moon circling the Earth. The orbit is also on a plane, but it is strongly inclined relative to the ecliptic plane, around 5 degrees.

The orbital plane of the moon intersects the Earth's orbital plane at two points, known as nodes. The Lunar Nodal Cycle is the name given to this regular orbital cycle.

A study, titled "Nodal Tidal Cycle of 18.6 Yr.: Its Importance in Sea-Level Curves of the East Coast of the United States and Its Value in Explaining Long-Term Sea-Level Changes," and published on GeoScienceWorld claimed the moon's orbital plane wobbles to a mean and minimum of +/- 5 degrees for 18.6 years.

Tides on Earth are exaggerated as the lunar plane is more closely aligned with the plane of the Earth's equator. In contrast, Earth's tides are comparatively subdued as the lunar plane tilts farther away from the equatorial plane,

The lunar nodal cycle was first formally documented in 1728. Still, keen astronomical observers have known about it for thousands of years.

The nodal cycle has a slow impact that few people note because they have been paying meticulous attention to the exact activity of the moon and tides for decades.

On May 26, there will be another "super full moon," which will be a perigean full moon like the one in April. Cities like Miami should predict tidal floods even with the lunar nodal period in its current phase.