Menai strait full moon and monster tides

Fri 13th January 2017

Winter storms, low pressures, a full moon and monster tides.  These are the ingredients for this weekend’s volatile cocktail of coastal crises.

If you look out of the window tonight and are lucky enough to see the moon, it’s not only a winter beacon of light but is a sign of big movements on the coastal seas and in the Menai Strait.  The perfect alignment of Sun, Earth and Moon happens two days after a full or new moon. This Saturday is when we get the big ‘Spring’ tides.

Film of the high tide turning, 13 January 2017
11am at the Menai Suspension Bridge

On Anglesey that tide is a wall of 7.5 metres of water, slowly filling the Menai Strait. Every 6hrs approximately 30 million cubic metres of water passes through the Strait. That’s 12,000 Olympic swimming pools or 20 Millennium Stadiums full of water – four times a day.

The Swellies is the narrowest, shallowest and most volatile section on the whole Strait. A wall of water is squeezed between the famous bridges at speeds up to 10kts (11.5 mph) To compare – Michael Phelps top swimming speed ever was 6mph, or if you were a runner, this would mean a marathon in 2.17hrs. Try keeping that up for six hours.

Film of the low tide turning, 9 April 2016
7.30pm at the Swellies


Tides and Storms

So, while we contemplate this perfect brew of tides and storms currently battering the East Coast, our biggest floods can also come without the help of the biggest tides. Atmospheric pressure can heighten or lower tidal heights by 1cm per millibar above or below the average of 1012mb. So, today on Anglesey it is reading 1016mb, meaning the pressure is pushing the water down 4cm. However the low pressure over the East coast of England is 980, meaning an extra 32cm of height.

High Tide at the Slipway Menai Bridge 13 Jan 11.03am

A final and unique feature of the Menai Strait is that unlike most tidal estuaries, it has two ends, or mouths feeding it. In simple terms, if the wind is strong from the south, it pushes more water in from Aber Menai all the way up to Beaumaris where the axis of the two tides lives. This is what created Gallows Point.

Low Tide at the Slipway, 6 Jan 17, 9.50am

That same wind also pushes more water up the Irish Sea, some of which will wrap itself around Puffin Island and flow South to Beaumaris. Once the tide starts heading out, that same wind stops the water flowing out of the Strait, creating an Aber Menai Plug and raising levels particularly around Moel Y Don.

So, tomorrow sees low pressure, high tides and strong Northerly winds, a perfect recipe for a RibRide through the Swellies. We are open all day and there is no such thing as bad weather, just bad clothing. So dress warm, give us a call or book online 24/7 and step aboard for another great Adventure with RibRide.