Sun’s and moon’s gravity on the earth will cause earth to bulge. When the water body flows through the bulgy region, the water appears to be flowing from high tide region to the low tide region.

When the sun, earth and moon align and forms line (a configuration known as syzygy), the tide’s range is at maximum. This is because, the opposite gravitational pull exerted by moon and sun don’t cancel each other at this configuration and tries to pull earth on both the opposite sides of earth. This will result in the bulgiest structure of earth causing the tides to be at its maximum during this time. Full moon