Supermoon, Eclipse And High Tides

Full Moon

When I began my study of hurricanes, and the threat of Storm Surge, it was important to learn something about the tides and the moon.  Storms that arrive at high tide have a much more significant coastal flooding impact.  Storms that arrive during abnormally high tides, can be particularly threatening.

On Sunday the moon’s orbit will be at it’s closest point (perigee) to the Earth, making it about 14% closer and 30% brighter.

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As well, the sun and moon will be lined up, causing a lunar eclipse as the moon enters the Earth’s shadow at 10:07pm Sunday evening 27 September.   By 11:47 pm it will be in the middle of the shadow, and under full eclipse, and emerge once again at 1:27am early Monday morning.

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This event is also unique, as the alignment of the Sun, Earth and Moon will maximize the astronomical high tide.  This 18 year event will not occur again until 2033!  There was a very interesting and devastating hurricane that affected the Maritimes in 1869, the Saxby Gale.  It’s arrival coincided with one of these very high tides, enhancing the flooding, damage, and loss of life.

Next week, the high tides will be higher than normal: for example, in Halifax, the high tide on Monday and Tuesday will exceed 2m.  This is about 30cm higher than a “regular” high tide.

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There may be some localized minor flooding in the Maritimes Monday or Tuesday from this high tide.  Since the sea-level has been rising (more than 30cm over the past century in Halifax), older infrastructure may be more at risk.  While a low pressure system with rain will cross the region on Tuesday, it does not appear to be very intense.  Some wave action in brisk winds may enhance the minor flooding.

 

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As I prepare this article, it is expected that skies will be mainly clear Sunday evening for good viewing of the large moon and the eclipse.

Folks living along the shore should keep an eye for any surprise winds that could enhance the high water levels on Monday and Tuesday. For comparison, the high tide for Hurricane Juan was less than 2m.  A 1.5m storm surge after high tide raised the water levels to a record 2.9m.

 

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