Today's ocean tides, in most areas of the globe, are predicted to be both the highest and lowest of the year -- and possibly of the last several years -- because of the particular alignment of the Earth, sun and moon. But the event is unlikely to excite much notice, unless there is also a severe coastal storm.
"It just depends where you are," said Stephen Gill, an oceanographer with the National Oceanic and Atmospheric Administration. "They'll be the highest this year for most places, but only by a tenth of a foot or so."
High tides occur at each full and new moon because the Earth, moon and sun are lined up. Today's record highs and lows are expected because yesterday's full moon occurred within three hours of perigee, the moment when the moon passes closest to Earth during each 27.5-day, elliptical orbit around the planet. The closer the two are to each other, the greater the mutual gravitational pull they exert -- making the high tides higher and, as the Earth rotates, the low tides lower.
Gill said yesterday's perigee brought the moon closer to Earth than at almost any time in the last decade. The moon's pull moves ocean waters horizontally in their basins, and because friction creates a lag time, the highest tides occur on the day after the full moon.
Though the sun is much farther away, it is so large that its gravitational pull also affects the tides. Higher-than-normal tides are expected again on New Year's Eve, when perigee will occur within 12 hours of December's second full moon, and on New Year's Day, because the Earth's orbit will bring it closer to the sun than at any other time during the year.