When trying to predict well into the future, we have to take into account the rise in global sea level. The further into the future we try and predict, the more significant this effect can become. The rise and fall in sea-level is caused by the earth rotating on its axis underneath these bulges of water. This is called the lunar tide . This is possibly the most common question staff at the laboratory are asked - and it could be something to do with the fact that many reference books explain it incorrectly.
Most people think the moon rotates round the earth.
The 'tide-generating' force is the difference between these two forces. On the surface of the earth nearest the moon, gravity is greater than the rotational force, and so there is a net force towards the moon causing a bulge towards the moon. On the opposite side of the earth, gravity is less as it is further from the moon, so the rotational force is dominant. Hence there is a net force away from the moon. It is this that creates the second bulge away from the moon.