The daily tidal range is greatest at the new moon and full moon, when the tidal pulls of the moon and sun are in phase with each other. This phenomenon is called a spring tide and is strongest when it coincides with the vernal or autumnal equinox.
Tidal range is the vertical difference between a high tide and its succeeding low tide. It is affected by the moon's orbit, the earth's orbit around the sun, local geography and weather effects such as strong winds. Tidal predictions published in government guides are based on astronomical data and do not include weather effects as these cannot be predicted much in advance.