Coastal areas in eastern North America and the United Kingdom – and no doubt elsewhere around the world – are experiencing exceptionally high tides this week, caused by Sunday’s supermoon. Although the tides should not be as high on Wednesday as they were on Monday and Tuesday of this week, heavy rains from Tropical Storm Joaquin, now in the western Atlantic, may combine with the tides to create a flood threat in the U.S. East. Read the WeatherChannel’s forecast for the U.S. East.
Astronomers who understand supermoons, which they call perigean full moons, had been expecting higher-than-usual tides. It’s not just a supermoon, though, causing the extra-high tides this time. The effect on the tides is being accentuated by the fact that we’re near the peak of an 18-6-year cycle of the moon, which features what astronomers call a minor lunar standstill. Follow the links below to learn more.
…Extremely heavy rain combined w/ windy conditions & record high tides from #supermoon, flooding is likely in many coastal areas…(cont)
— Maritime Wx Agency (@maritimeweather) September 29, 2015
— Emily Michot (@EmilyMichot) September 28, 2015
Monday and Tuesday’s high tides in North America. The Miami Herald posted a video and photos on Tuesday showing they call in Florida a king tide. This extra high tides – known as a perigean spring tide to scientists – hit Miami Beach on Sunday and Monday (September 27 and 28, 2015). Higher-than-usual tides flooded parts of South Florida, and other parts of the state.
North Carolina beaches were stormy this past weekend, and flooding hit particularly hard at North Topsail Beach. Video here.
South Carolina’s high tides can be seen in the photos below.
People were also talking about the extra-high tides further up the U.S. East coast, while bracing for heavy rains from Tropical Storm Joaquin.
The rainfall forecast for the coming week shows heavy rain across the U.S. Mid-Atlantic and Northeast, mainly from Tropical Storm Joaquin interacting with a stalled front. Potential flooding will depend on the storm track, the amount of rain and, in some places, the height of the tides. The tide chart below is for Atlantic City, New Jersey.
Tidal guidance now pointing to at least 3 consecutive flooding high tides. Not exactly ideal. pic.twitter.com/KkAtTf4xzG
— StormForce_1 (@StormForce_1) September 29, 2015
In New Brunswick – bordering the U.S. in eastern Canada – Tuesday’s tides hit a peak that had not been reached in nearly two decades at the Bay of Fundy, which boasts the highest tides in the world. Bay of Fundy tides of 14.2 meters (about 50 feet) were expected, according to CBCNews in New Brunswick.
— New Brunswick (@SeeNewBrunswick) September 29, 2015
On Tuesday night, there were 4 flood warnings and 27 alerts in effect in England, and 3 flood warnings and 8 alerts in effect in Wales. A flood warning means that flooding is expected. A flood alert means that flooding is possible. Go directly to the Met Office for the latest information.
Or follow the UK’s flood warnings and alerts via @FloodAlerts on Twitter, licensed by the UK’s Environmental Agency.
— WalesOnline (@WalesOnline) September 29, 2015
The gravity of the sun and moon always combine to create the tides. Consider that – each month, on the day of the full moon – the moon, Earth and sun are aligned, with Earth in between. This line-up creates wide-ranging tides, known as spring tides. High spring tides climb up especially high, and on the same day low tides plunge especially low. They happen every month.
A supermoon is a full moon with something extra. It’s a full moon that happens to be at its closest to Earth (perigee) for that particular month. Sunday’s full moon reaches its closest point to Earth within an hour of the crest of its full phase. It also underwent an eclipse. The extra-close full moon accentuates these monthly (full moon) spring tides all the more.
And that’s not all, for this particular supermoon. This year, as part of one of the heavens’ regular cycles, the sun and moon are positioned over Earth’s equator in such a way to accentuate the tides. This pattern – which features what’s called a minor lunar standstill by astronomers – is causing a smaller Harvest Moon effect this year (the recent full moon was the Northern Hemisphere’s closest full moon to the autumn equinox and therefore carried the name Harvest Moon).
Meanwhile, it’s causing a stronger-than-usual pull on the tides. Read more about the minor lunar standstill.
In settled weather, the high spring tides are a curiosity or nuisance, mainly. But watch out for storms, which have a large potential to accentuate high spring tides and cause serious flooding.
Bottom line: Sunday’s supermoon, combined with an 18.6-year cycle of the moon, have caused high tides on both sides of the Atlantic this week. There were many flood warnings and alerts in the UK on Tuesday. In eastern North America, Tropical Storm Joaquin might combine with high tides to cause flooding.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.