The rare supermoon seen in the skies this week presented a natural wonder for many stargazers to stare at and photograph, but there are side effects related to the lunar event that have seen high tides and flooding in parts of America.

Monday night’s supermoon was shrouded in cloud for some, but for those who had clear skies the full lunar disk appeared 14 per cent bigger and 30 per cent brighter than usual as it came closer to the Earth than it has been in nearly 70 years.

One of the adverse effects of the supermoon is a stronger high tide due to the increased gravitational pull, however, and flooding has been seen in areas of Florida as a result.

South Florida saw heavy flooding hit coastal areas including Fort Lauderdale and Miami on Sunday and Monday. In these areas, the supermoon has increased the effect of the seasonal king tides, which occur one to two times a year, causing the lowest lying areas to be immersed in water.

A king tide, which can also be known as a perigean spring tide, is “the highest predicted high tide of the year at a coastal location,” and occurs when “the orbits and alignment of the Earth, moon, and sun combine to produce the greatest tidal effects of the year," according to the US Environmental Protection Agency.

Authorities in Fort Lauderdale had already announced planned road closures for the morning and evening in anticipation of the flooding, targeting streets that had previously filled with water when the last king tides were seen.

“The gravitational pull has caused our high tides to be a little bit higher than they would have without the supermoon,” Dr Tiffany Troxler, director of Florida International University’s Sea Level Solutions Centre, told CBS News. People have been tweeting pictures of the flooding, showing water in the streets.

Residents of New Brunswick in Canada have been warned that the biggest tides of the year will hit on Wednesday, risking coastal flooding in the Minas Basin in Nova Scotia and the Bay of Fundy, while Environment Canada issued a special weather statement for a number of areas, including Fundy National Park.

“The tides are well above normal because of this supermoon and with a little bit of low pressure on Wednesday, the tides may push to a level where there may be some coastal flooding in parts of Fundy and the Minas Basin, CBCNews’ meteorologist Jim Abraham said. 

While supermoons are fairly common – occurring every 14 months or so – this particular lunar event marked the shortest distance between the moon and the Earth that has been seen since 1948.