The textbook picture has two bulges of water, one under the Moon and one on the far side, with the Earth turning beneath them. That gives two high waters in each lunar day of 24 h 50 min. If the sea could keep up, high water would race round the equator at about 1,600 km/h, staying under the Moon.
It cannot keep up. The tide is a very long wave, and its speed depends on the depth: in 4 km of ocean it travels at about 700 km/h, less than half the speed it would need. The continents also block the way round. So in each ocean basin the tide runs as a wave of its own, and the Earth's rotation turns it round amphidromic points (the circles), where there is almost no tide at all.
Every coast therefore has its own fixed delay behind the Moon, and its own height. Where a bay or sea resonates with the 12-hour rhythm, the tide grows large, as in the Bay of Fundy, the Bristol Channel and Patagonia. The Mediterranean and the Baltic are nearly closed off and have small tides. The North Sea gets its tide from the Atlantic, round the north of Scotland and through the Dover Strait, and it runs anticlockwise round three amphidromes of its own. That is why high water at Vlissingen comes hours after the Moon has passed.
The Sun raises a tide too, a little under half the Moon's. At new and full moon the two pull in line and give spring tide. This is 11 and 12 October 2026, just after the new moon of 10 October. In the North Sea the biggest tides come about two days after new moon, the time the tide wave needs to arrive from the Atlantic.
Source: E.U. Copernicus Marine Service, Global Ocean Physics Analysis and Forecast, hourly ocean tide elevation at 1/3°. Moon and Sun positions computed from their orbits
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