out and about - 2018
04 March 2018 .............. A very high tide at Rhosneigr
Out on my bike this morning, and the back roads still had a bit too much snow on them for comfort, so I ended up going round down by the coast in Rhosneigr - and coincidentally, I arrived there pretty close to high tide - it was a very high tide, one of the biggest I have seen there.
Looking at the EasyTide website, it was showing a predicted high tide at Holyhead of 6 metres - that`s a big tide.
Looking out over the bay out from Rhosneigr and Traeth Crigyll, and you can see how much of Ynys Feirig, the long thin island, or chain of islands, is under water.
I didn`t know there were so many cormorants around Rhosneigr - I suppose normally they have a much greater area of rocks to use - Ynysoedd Gwylanod and Rhoscolyn Beacon are still standing up well above the sea, and Rhoscolyn Head just sneaks into the picture -
Another interesting thing - now I had always assumed that the trig point on the rocks was just that - it was a trig point.
But now I wonder if it has another significance - because if it was a normal trig point, they would have put it on the higher rocks at the back - but with this 6 metre tide, it was getting its feet wet.
With the huge low pressure that is sitting over the UK and most of western Europe, the sea level will be elevated and the actual tide would be above 6 metres at Holyhead - so maybe that trig point is actually marking the height of the Highest Astronomical Tide level.
Doing a little digging on the web I found that the Highest Astronomical Tide level for Holyhead is 6.33 metres, 0.33 metres above the predicted tide height of 6 metres.
The low pressure is around 984 mbar , and tide levels are predicted assuming a pressure of 1013 mb, so that is a difference of 29 mbar - as a rough guide 1 mb of pressure difference changes the tide height by 1 cm - so a difference of 29 mbar results in a tide rise height of 29 cms - which just about takes us up to the Highest Astronomical Tide height of 6.33 metres - so that confirms that that trig point is sitting on a rock at the Highest Astronomical Tide height.
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