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High ‘supermoon tides’ strike coasts

Sunday’s supermoon, combined with an 18.6-year lunar cycle, caused high tides on both sides of the Atlantic this week. There were many flood warnings and alerts in effect in the UK on Tuesday night. In eastern North America, Tropical Storm Joaquin might combine with high tides to cause flooding.

Coastal areas are reporting higher-than-usual tides caused by Sunday's supermoon.  Along the east coast of the U.S., severe weather from Tropical Storm Joaquin could cause flooding.

Coastal areas are reporting higher-than-usual tides from Sunday’s supermoon. Along the east coast of the U.S., severe weather from a tropical storm could cause flooding.

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.

Monday and Tuesday’s high tides in eastern North America

High tides in the UK

The supermoon’s effect on the tides.

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.

Live5News has a report on flooding in Charleston, South Carolina.

Live5News has a report on flooding in Charleston, South Carolina.

Deik Haigler Photography wrote on Facebook on September 27:

Deik Haigler Photography wrote on Facebook on September 27: “We almost got stuck out the Marsh Boardwalk when this King High Tide came in over the boardwalk…”

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.

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.

View larger and most recent. | As of Tuesday night, many flood warnings and alerts were still in effect for England and Wales.  Get the latest from the UK's Met Office.

View larger and most recent. | As of Tuesday night, many flood warnings and alerts were still in effect for England and Wales. Get the latest from the UK’s Met Office.

High tides in the UK. Various media, including the BBC and The Telegraph, reported high tides in parts of the UK early this week.

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.

High tide at Mersea Island, Essex, England this week.  Photo by Stephen Huntley of The Telegraph.

High tide at Mersea Island, Essex, England this week. Photo by Stephen Huntley of The Telegraph.

How does a supermoon affect the tides? All full moons bring larger-than-usual tides, and supermoons – called perigean full moons by scientists – bring the highest (and lowest) tides of all.

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.

View larger. | Perigean spring tides - aka supermoon tides - explained, via NOAA.

View larger. | Perigean spring tides – aka supermoon tides – explained, via NOAA.

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.

Read more about Florida’s high tides this week from the Miami Herald

Read more about North Carolina’s flooding from WITN

Read more about the UK’s high tides from The Telegraph

Deborah Byrd

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