Why do the two high tides of the same day vary in height?
There are many periodic effects which determine the height of tides, such as the angle between Moon and Sun, the variation in the distances of the Moon from the Earth and the Earth from the Sun. All these effects will have changed slightly in the 12 hour interval between successive high tides. It isn’t true for every port on every date that the first bulge is lower than the second. Check some other ports and dates and you’ll find the opposite is just as likely to be true.
