Sandy from Boston: the day after

A little after 4 am this morning I was awakened by the full moon shining in my window. The winds had calmed, the rain ended and the clouds had parted at least momentarily.  The Old Farmer’s Almanac calls this the Full Hunter’s moon.  Now we have alternating sun and clouds.  (And a brief shower when I went out to buy Halloween candy.)

Boston and Massachusetts, except for the south coast, were as the Boston Globe put it in the headline to the Metro section, “still walloped” even far from the center.  After a while I just couldn’t watch television coverage as they showed Seaside Heights on the Jersey Shore basically under water.  I can only imagine what Long Beach Island where I often summered as a child looks like.  And Manhattan and the Red Hook neighborhood of Brooklyn.  Yes, Boston was lucky.

But we were not without damage which shows the size and strength of the storm.  That size and strength was magnified by that beautiful Hunter’s moon outside my window.  Here is how it works.  This is from the EarthSky News.

Of course, we all know the moon is primarily responsible for the rising and falling of ocean tides.  In most places, but not everywhere, there are two high tides and two low tides a day.  That’s true of the U.S. East Coast, where Sandy is having its effect.  That effect can’t be predicted precisely because – for any particular spot on Earth’s surface – the height of the tides and their fluctuation in time depends not only on the moon, but also on the sun – and also on the shape of the specific beach, the larger coastline, the angle of the seabed leading up to land, and the prevailing ocean currents and winds.

The difference in height between high and low waters varies as the moon waxes and wanes from new to full and back to new again.  The higher tides are called spring tides (nothing to do with season of spring).  The lower tides are called neap tides.  It’s a spring tides that’s happening around this weekend, as Sandy is sweeping closer to U.S. shores.

Around each new moon and full moon – when the sun, Earth, and moon are located more or less on a line in space – the range between high and low tides is greatest.  These are called spring tides.  Image via physicalgeography.net

Spring tides.  Full moon this month comes on October 29 at 19:49 Universal Time (or 2:49 p.m. Central Daylight Time in North America).  Around each new moon and full moon, the sun, Earth, and moon arrange themselves more or less along a line in space. Then the moon’s pull on the tides increases, because the gravity of the sun reinforces the moon’s gravity.  In fact, the height of the average solar tide is about 50% the average lunar tide.  Thus, at new moon or full moon, the tide’s range is at its maximum.  This is the spring tide: the highest (and lowest) tide.  Spring tides are not named for the season.  This is spring in the sense of jump, burst forth, rise.  So spring tides bring the most extreme high and low tides every month, and they happen around full and new moon.

It’s when a spring tide coincides with a time of heavy winds and rain – flooding due to a weather extreme – that the most extreme flooding occurs.  That’s the case this weekend.  There is one small bit of luck.  That is, the moon is not near perigee, or closest to Earth for the month.  In fact, the moon will be at apogee- farthest from Earth for the month – on November 1.  A full moon at perigee during a destructive hurricane would be bad news indeed.  A full moon at apogee is slightly less bad, but still bad.

So, yes the full moon didn’t help, but I guess it could have been worse.

This is from Quincy, MA just south of Boston.

Hurricane Sandy in Quincy, Mass. -- Photo couresty: Dawn Gaffney

Photograph by Dawn Gaffney

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