Tuesday, December 10, 2013
They come and they go. Twice each day, right on schedule. A simple tide chart will tell you months in advance when high tides will arrive on any given day, and how high they will be.
But something has been messing with the ebb and flow along the entire East Coast in recent weeks, and scientists aren't exactly sure what.
Surprised researchers are calling it an anomaly that began around June 19, pushing tides 6 inches to 2 feet above predicted levels. It lasted until this week, when the Atlantic Ocean appeared to fall back in line with the National Oceanic and Atmospheric Administration's official tide charts.
''It happened all the way from Portland to Florida,'' said Stephen Gill, senior scientist at NOAA's tide and current program in Silver Spring, Md. ''We see these kind of deviations up and down the East Coast, but we don't see them all at once like we just did.''
Though the scientists admitted to being stumped, at least at first, there has been no sense of alarm.
It isn't global warming or melting ice sheets, they said. The earth, moon and sun are all behaving as they should. And it isn't a case of too many people leaning the same way, Gill said.
It simply might be a reminder that tides aren't entirely predictable after all.
Winds, ocean currents and atmospheric pressure all can affect tides. The winds that fuel nor'easters, for example, create tidal surges that flood Commercial Street and wash away seawalls in York County.
''Anytime you have a northeast wind, the water piles up,'' said John Jensenius, warning coordination meteorologist with the National Weather Service in Gray.
And Maine had enough northeast winds during the past six weeks to trigger repeated warnings about higher-than-expected tides, he said.
But weather typically affects the tides in one region, not along the entire coast. And researchers couldn't find a weather pattern big enough, on its own, to explain such a large, prolonged shift in the tides.
The leading explanation now is a freak combination of weather and currents. A ''widespread wind field'' over the Atlantic Ocean happened to coincide with a subtle change in the Florida Current, Gill said.
The Florida Current is an underwater stream that feeds into the Gulf Stream and, apparently, can influence the depth of water on a beach in New England. Scientists believe the current weakened around June 19, although they aren't sure why.
''This particular anomaly was just kind of new because it hasn't occurred at the same time,'' Gill said. ''That usually doesn't happen.''
So, what we really want to know is this: Did the wind field or the Florida Current or the tidal anomaly have anything to do with all that rain in June and July? And does this mean we can put away the umbrellas?
''I'm sure it's all connected somehow,'' Dill said, trying not to disappoint. ''But it's pretty chaotic, this system we live in.''
In other words, if the tides can catch you by surprise, don't try predicting the weather.
Staff Writer John Richardson can be contacted at 791-6324 or at: