Evidence of a higher than usual high tide at Pt Chevalier beach

A lunchtime high tide on a relatively calm day brought quite a few people to Pt Chevalier beach on Monday the 6th of January. A line of  debris along the pavement is evidence that a recent higher than usual tide reached beyond the small sea wall. This could have occurred yesterday when we were faced with the relatively strong westerly at Kohimarama as this would have been heading straight into the west-facing Pt Chevalier beach. The combined effects of a spring tide (3.6m), strong onshore wind and low air pressure (usually accompanied by unsettled weather conditions) usually generates a higher than usual tide, and it is likely to be what occurred at Pt Chevalier yesterday.

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Evidence of a recent very high tide at Pt Chevalier beach

The relationship between air / ambient / atmospheric pressure and water level is something that completely astounds me. I had thought that water always took up the same amount of space but when atmospheric pressure is high it pushes down onto water making the level lower. In New Zealand this is what happens on a calm, sunny day. Low barometric pressure exerts less force upon the surface of the water, so it is, in effect, higher and can add a few cm to a high tide. The recent high tide has formed a small dune scarp or ridge of sand in front of the stone wall as waves have shifted sand from here to elsewhere.

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A small dune ‘scarp’ has formed in front of the pavement at Pt Chevalier beach

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