Moon and storm cause flooding

For the second time in a month, storms have coincided with socalled supermoons, and coastlines have been flooded.

There is a link, although it’s as much because the Moon is full, rather than because it is super which is just a way of describing a full moon that happens when the Moon is near the closest point in its orbit to Earth.

Tides are a bit higher and a bit lower than average when the Moon is full or new, so tide ranges - the vertical difference between high tide and the following low tide - have a fortnightly cycle.

Then, if a full or new moon also coincides with the closest point the Moon gets to the Earth during its orbit - known as perigee - the tides can get a bit higher or lower again.

‘‘Tides are caused by the gravity of the Moon and the Sun,’’ Dr Claire Bretherton, science curator at Space Place in Wellington, said. ‘‘It [high tides] certainly would be linked to the full moon we had in the early hours of this morning.’’

When full moon happened close to perigee that could also have an impact on tide height.

With a gap of 27 hours between perigee and the full moon early Thursday, it was open to interpretation whether there was a genuine supermoon overnight. ‘‘A lot of people I know have been talking of it as an almost supermoon,’’ she said.

Tides roll around the planet as the ocean is ‘‘pulled’’ back and forth as the Moon and the Sun interact with the Earth in their monthly and yearly orbits. The Moon’s impact is considerably greater than that of the Sun because it is so close to the Earth.

Tidal ranges are slightly larger during full and new moons - when the Earth, Sun and Moon are nearly in alignment - because the gravitational pull of the Sun is added to the pull of the Moon on the Earth, causing the oceans to bulge a bit more than usual. These are the times of king, or spring, tides.

The Moon reaches perigee about once every 28 days. At these times the Moon’s gravitational pull is strongest, and there is a slight increase in the average range of tides.

About three or four times a year, the full or new moon happens near the time of perigee. At those times we have what are called perigean spring tides.