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Hurricane Sandy: Does a full moon cause high tides? How?

Forecasters warn that storm surges from Hurricane Sandy could be particularly powerful, because the storm coincides with a full moon. How does that work, exactly?


NOAA's GOES East satellite snapped this image of Hurricane Sandy at 10:45 a.m. EDT (1445 UTC) on Oct. 24, 2012, as it was headed for landfall on Jamaica.


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Heaven and Earth may be aligning to turn Hurricane Sandy into a real monster, just in time for Halloween.

Forecasters expect Sandy to make landfall along the mid-Atlantic coast of the United States on Monday or Tuesday (Oct. 29 or 30). It may merge with a separate tempest hitting the region at about that time, creating an immensely powerful "Frankenstorm" whose effects could be magnified by the full moon.

When the moon waxes to its full phase Monday afternoon, high tides along the Eastern Seaboard will rise about 20 percent higher than normal, even without the help of Sandy's storm surge, said Joe Rao, a meteorologist for News 12 in Westchester, N.Y. (Storm surges occur when a hurricane's winds push the water surface above normal levels.)

"Add a big storm, and the full moon will only serve to exacerbate the situation by helping to accentuate the higher-than-normal water levels, possibly leading to moderate or major coastal flooding and beach erosion," Rao told OurAmazingPlanet via email.

A gravitational lag usually causes the highest tides to come a day or two after every full moon, he added.

"So the worst coastal flooding wrought by Sandy might actually come on Tuesday, all depending on exactly where and when the storm makes landfall," said Rao, who is also the Night Sky Columnist for OurAmazingPlanet sister site [How to Prepare for Hurricane Sandy]

At full moon, the Earth, sun and moon are arranged in a line, with Earth in the middle. Tidal ranges are especially high at this time because the gravitational tugs of the sun and moon on our planet reinforce each other. The same effect is felt at new moon, when the three bodies all line up, with the moon between Earth and the sun.


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