Lunitidal interval

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The lunitidal interval is also called the Greenwich high water interval (HWI), it is the length of time from when the moon passes over a meridian and the next high tide at that meridian. Tides are known to be mainly caused by the moon's gravity. Theoretically, high tide happens when the moon is at meridian. However, there is actually a delay that depends on many complicated factors.

The length of lunitidal interval differs on all shores in the world. For any particular shore it is, on average, a constant value. Knowing the lunitidal interval, it is possible to predict how long after the moon moves to meridian until high tide will occur.

The approximate lunitidal interval can be calculated if the moon rise, moon set & high tide timings are known. These timings can be obtained if the cordinates for your region are known or even from local media.

First you will have to calculate the moon up time of your area . This is the mid point time between the moon rise and moon set. This will be time that the moon is directly above the meridian. The lunitidal interval is the difference between the moon up time and the next high tide.