Boston’s Long Wharf was covered in water when the king tides hit Massachusetts last month. —Photo courtesy Jean Nagy

Last month’s king tides drew scores of pedestrians to Boston’s waterfront to observe—and splash in—the unusually high waters.

This week, they’re back. And they might be even higher.

The extreme tides are a normal occurrence, though the increasing degree to which they have flooded local coasts has attracted recent attention.

According to the local National Weather Service office in Boston, the astronomically-caused tides, bolstered by a coastal storm, are expected to bring higher waters than what was seen in October.

The NWS forecasts the king tides to reach a peak high tide of 12.5 feet (about two feet higher than normal high tides) around noon Tuesday. But waves from a storm forecast to hit midday could bring an 0.5 to 1 foot of additional surge, according to the service.


With wind and waves, Boston’s king tides in October reached a peak of 12.8 feet, according to the NWS. They were originally forecasted to reach 12.3 feet, 0.2 feet less than what is expected Tuesday (without taking weather into account).

Wednesday’s king tides are expected to reach 12.4 feet without weather.

The reason for their return? Monday night’s supermoon.

King tides occur when the Earth, moon, and sun align so that they are as close to each other as possible in their orbits. According to NASA, Monday will be the closest the moon has been to Earth since 1948.

Or as NASA scientists put it, “an extra supermoon.”

According to the agency, the moon won’t be this close to Earth until 2034.

Because of the astronomical and climate factors, the NWS said Sunday that minor to moderate flooding could impact coastal locations this week. More information would be available Monday, the service said.