The New Moon marks the beginning of a tidal month, and it’s an unassuming start at that – because the moon is directly between the sun and earth, sunlight is on the face we can’t see so it appears completely invisible in the sky. The New Moon can even hide the sun, but for this to happen there must be a rare synchronisation of orbits where the sun appears especially small and the moon exceptionally large. This is the famous solar eclipse, but less known is the accompanying ‘Perigean Spring Tide’, named because it only happens when the moon is at Perigee [the closest point to earth on its elliptical orbit]. This makes the New Moon appear large enough to block out the sun, and the increased gravitational pull creates exceptionally powerful tides.
Although Perigean Spring Tides are rare, the standard Spring Tide is much more common. Contrary to popular belief, springs don’t only happen in spring. Instead, we experience them every fortnight when the sun, moon and earth are aligned at the Full Moon and New Moon. The effect is higher highs and lower lows than the weeks either side, and this is because the gravitational pulls from the sun and moon are working together. On these days the transformation of our coastlines every six hours is awe-inspiring, but even more so is the phenomena that creates this change; a set of long-period waves flowing along our shores with high tide at their peaks and low tide at their troughs. If magic seaweed were to summarise the tide wave of my local beach in Kent during the New Moon it would be 36ft@6hrs, much more fearsome than the 3ft@6secs we get in the winter after a good blow.
These enormous tide waves power currents racing along the coast and they have a massive effect on anyone swimming, sailing, paddleboarding, scuba diving – literally every activity. To understand the connection between the waves and currents, think of the phenomena of water draining from a beach just before a tsunami. This is the trough of the tidal wave, and all the water is being sucked towards the peak – when it arrives, the water then surges towards the shore. Now take this concept but change a tidal wave into a tide wave, spin it 90 degrees so instead of the wave heading towards the shore it’s running along it, and you’ll understand how tidal currents work. Following this theory, if you’re on Britain’s east coast [where the tide wave travels south] at low tide you’ll be sucked north, and at high tide you’ll be pushed south with the peak of the wave. In essence, you’ll be riding the tide wave.
On an open coast at Spring Tides, the fastest currents might flow around 4 knots, so it takes a little imagination to truly ride the wave. However, in some places the powerful tides at New Moon can create intense surfing waves. And unlike beach waves that are over in seconds, these waves can be ridden for hours at a time. A perfect example is The Bitches in Wales, not named because of the bitchin’ rides but because that’s what the reef they break on is called. When the tide is rising, it pours over the reef and the tidal currents flow down a series of ramps, rising into standing waves that stay in one place while the water flows through at 10 knots [accelerated by the construction in the coastline around St Davids, Pembrokeshire]. At the New Moon this is not an environment for beginners, and even experienced surfers should wear helmets and buoyancy aids because when you come off the wave you’ll be catapulted into a cacophony of whitewater, with a few whirlpools thrown in for good measure.
The best feature of tide waves is that they appear like clockwork, directly synchronised with the moon phase. At every New Moon, the peak of the tide wave will pass your beach at the same time – in Lands End it’s around 6am/6pm and where I live in Deal high tide is around 12am/12pm [this is because it takes 6 hours for the wave to travel up the English Channel from Lands End to Deal]. It will then be 50 minutes later every day, a result of the simultaneous orbit of the moon as the earth rotates. The effect is that a week after New Moon tides are 6 hours later, two weeks after they are 12 hours later, three weeks after they are 18 hours later and a month after they are 24 hours later. Because New Moon happens once a month, this explains how tides essentially ‘reset’ themselves. Using this knowledge, and an understanding of the tide waves around the world, you could predict the tide anywhere on the planet, any day, by simply observing how many days after New Moon it is. And to do that, all you need to do is look at which side of the moon is illuminated, and how much.
Next week is the First Quarter moon phase with the right side lit up, and William will explore the effects this will have on our saltwater adventures. For more tidal information, visit tidalcompass.com or follow Tidal Compass on Instagram.