By Tim O’Meilia

The autumnal equinox arrives Sept. 23 and that means higher than usual spring tides could threaten to slosh down coastal streets this fall.
    Huh?  Spring tides in the fall?
    “It all has to do with the Earth, the sun and the moon lining up during the full moon and the new moon. And it has to do with the equinox,” said National Weather Service meteorologist Dave Ross in mysteriously vague terms.
    And twice-monthly spring tides have nothing to do with the seasons. The strongest tides — usually 20 percent higher than normal — occur during the new moon when the gravitational pull of the sun and moon are aligned on one side of the Earth.
    Add a pinch of help from the equinox, when the sun crosses the Earth’s equator, and the spring tides that follow are usually the strongest of the year.
    The Boynton Inlet will have tides 3.8 feet higher than mean low water Sept. 27-28 and 3.9 feet higher Oct. 27, the National Oceanic and Atmospheric Administration (NOAA) forecasts.
Compare those with other high tides that typically reach 2.8 to 3.1 feet above the mean low water levels.
 Along the Intracoastal Waterway near Highland Beach, tides will rise 3.7 feet higher Sept. 27-28 and 3.9 feet Oct. 27. At Lake Boca, near the Boca Inlet, the September highest tides are 3.5 feet Sept 27-28 and 3.6 feet Oct. 27.
    But the biggest difference will be along the Intracoastal Waterway in Ocean Ridge. The Sept. 27-28 tide will reach 4 feet higher and 4.1 feet Oct. 27.
    The high tides of autumn sometimes have caused street flooding, but many coastal towns have updated their drainage systems in recent years. Ocean Ridge, for example, installed $4 million in improvements near Woolbright Road several years ago and another project is under way at the end of Coconut Lane to ease flooding problems.
    Occasionally silt buildup on the ocean side of the Ocean Avenue bridge will flood the street, as it did several months ago.
    “Our main concern is not storm surge because of the coastal ridge. Our concern is flow into the inlet that will hit us from behind,” said Ocean Ridge Police Chief Chris Yannuzzi.
    The same is true for Highland Beach, where flooding from the Intracoastal is more worrisome than ocean tides.
    Two years ago, Manalapan cured its frequent flooding problem along State Road A1A near the Ritz-Carlton and the Plaza del Mar with a state-financed drainage program that installed new drainage and raised the road 18 inches.
    “It happens every year,” said meteorologist Ross. “We have the spring tides and the equinox to enhance them even more.”
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