A slow-moving September nor'easter knocked out power to about 136,000 homes and businesses across New Jersey, New York, Connecticut, Massachusetts and Rhode Island at its Sunday morning peak, while high tides boosted by the month's full moon pushed seawater into coastal streets for days. Outages had fallen to about 82,000 by Sunday afternoon, according to PowerOutage.us figures cited in Yahoo News live coverage.

The storm turned deadly in Brooklyn, where New York City Housing Authority employee Leighton Brown, 56, was killed Saturday afternoon when a tree fell on him near the Cypress Hills Houses in East New York, CBS New York reported. The storm also produced a wind gust of 74 mph in Surf City, New Jersey, and 81 mph at Montauk Point, New York, on Saturday, The Weather Channel reported.

The storm weakened and drifted offshore on Monday, Sept. 28, after one more day of rain in New England and a flood watch for Boston. For shoreline residents, the key lesson is timing. The worst water came with each high tide, not necessarily with the strongest wind or rain.

Wind Pushed the Water, the Moon Raised the Floor

Coastal flooding during a nor'easter is a stacking problem. Persistent onshore winds push ocean water toward the coast and into bays, a rise known as storm surge, and the astronomical tide sets the baseline that surge sits on.

Around full and new moons, the Earth, Moon, and Sun are nearly aligned, and the Sun's gravitational pull adds to the Moon's. According to NOAA's National Ocean Service, that alignment produces spring tides, with high tides that are higher than average. The name has nothing to do with the season.

This storm arrived during that window. The Weather Channel reported that the highest water levels came with Saturday's high tides, boosted by Saturday's full moon, and that 25 gauges reached major flood stage during Saturday afternoon's high tide.

The storm's slow pace made things worse. Because the nor'easter lingered for days, its winds kept piling water along the coast across many tide cycles, and most of the Atlantic coast sees two high tides a day. NOAA notes that when a coastal storm strikes during an especially high spring tide, flooding can be significantly worse than it otherwise would have been.

From the Outer Banks to Boston

The flooding began well south of New England. Minor to moderate coastal flooding hit parts of the Jersey Shore and southeast Virginia on Wednesday, with flooding reported in downtown Norfolk, Smithfield and Suffolk. On Thursday, ocean overwash closed a 16-mile stretch of North Carolina Highway 12 on the Outer Banks, and rising water forced the cancellation of Maryland's Oceans Calling Festival, The Weather Channel reported.

The storm peaked in the Northeast over the weekend. New Jersey accounted for about 57,700 outages as of about 10:30 a.m. Sunday, including more than 24,000 in Ocean County, according to the Yahoo News live coverage. New Jersey Gov. Mikie Sherrill warned that more flooding was possible with the next high tides. "To be clear: we are not out of the woods just yet," she said, NBC New York reported. CNN reported that water levels in Atlantic City reached their highest point since Superstorm Sandy in 2012.

Rain was heavy as well. Widespread totals reached 2 to 5 inches, with the highest reported total of 6.73 inches in Plymouth, Massachusetts, according to The Weather Channel. Repeated pounding from high surf also caused beach erosion that forecasters said could reach extreme levels along some stretches.

Who Faces the Greatest Risk Now

As of early Monday, most National Weather Service coastal flood warnings had been allowed to expire, though a few remained for Delaware and New Jersey, and at least minor high tide flooding was expected in parts of New England through Monday. The Weather Channel noted that because soils were saturated, it would not take much additional rain to trigger flash flooding.

Residents should check their local National Weather Service office and follow local emergency management, since conditions vary widely by town and by the timing of each tide.

Households still without power should treat every downed line as live, keep generators outdoors and away from windows, and report outages to their utility. Drivers should never enter flooded roads, since saltwater can hide washed-out pavement and damage vehicles quickly.

Homeowners dealing with water damage should photograph it before cleanup. Standard homeowners policies generally do not cover flood damage, which usually requires separate flood insurance, and beach towns will be assessing erosion that could weaken the dunes protecting homes.

After the Storm, a Longer Tide Problem

The storm also illustrates a longer-term trend. NOAA expects minor high tide flooding around the highest spring tides to increase as sea level rises relative to the land. That means the same combination of onshore wind and elevated tides that caused days of flooding this week could produce flooding more often in the future, even from weaker storms.

The most useful step for coastal residents is to learn their local tide schedule and flood stages, which NOAA publishes for monitoring stations along the coast. The next full moon arrives in late October, and coastal flooding risk will rise again if a strong onshore wind event coincides with it.

What Readers Want to Know

How many people lost power in the nor'easter?

Outages across New Jersey, New York, Connecticut, Massachusetts and Rhode Island peaked at about 136,000 customers Sunday morning and fell to about 82,000 by Sunday afternoon, according to PowerOutage.us figures.

Why did the full moon make flooding worse?

At full and new moons, the Moon's and Sun's gravitational pulls combine to produce spring tides, which have higher high tides. Storm surge from onshore winds added to those already elevated tides.

Why did the flooding keep happening day after day?

The nor'easter moved slowly, so its winds kept pushing water toward the coast over many tide cycles. Most of the coast sees two high tides a day, and each one brought a new round of flooding.

Which areas were hit hardest?

Coastal flooding stretched from North Carolina's Outer Banks and southeast Virginia to the Jersey Shore, Long Island, New York City, and southern New England. Plymouth, Massachusetts, reported 6.73 inches of rain.

Is the nor'easter over?

The storm weakened and moved offshore on Monday. Residents should still check local National Weather Service offices for any remaining coastal flood alerts.

Does homeowners insurance cover flood damage from a nor'easter?

Standard homeowners policies generally do not cover flooding. Coverage usually requires a separate flood insurance policy.