A powerful spring storm that inundated the entire East Coast pounded the Vineyard south shore with heavy seas this week, marrying with extreme tides to carve a substantial breach through Norton Point Beach at Katama at the extreme southeastern end of Edgartown.

The event leaves Chappaquiddick a true island for the first time in more than a quarter-century.

Buoyed by extreme lunar tides and gale-force winds, the waters of Katama Bay broke through a storm-battered barrier beach late Monday night and early Tuesday morning and, as of yesterday afternoon, was still running a deep channel into the Atlantic Ocean. The combination of bay currents and ocean waves resulted in a spectacular collision of force.

David Belcher, Chappaquiddick property manager for The Trustees of Reservations, said yesterday that the breach was more than 200 yards across and still growing.

It is not known how long the opening will last before it naturally fills in with sand. Previous breaches in the first half of the 20th century lasted for years, while the last few breaks at Norton Point closed within days or months.

Christopher Kennedy, Islands regional director for the Trustees, the conservation organization which manages Norton Point, said he expects this latest geological split to stick around for a while.

“This clearly is a major breach,” Mr. Kennedy said on Tuesday, after visiting the point. “It’s really something to see, just the sheer volume of water rushing through there. I don’t think this thing is going to heal over in the short term.Éd

For the time being, all vehicle access is prohibited from both the Chappaquiddick and Katama ends of the beach. Mr. Kennedy said it may take weeks for the sand to stabilize, but assured that the Trustees will reopen the beach as soon as it is safe.

He also asked people keep the event in perspective, as the breach represents a natural cycle that will likely improve the health of the bay.

“This is not a catastrophe,” Mr. Kennedy said. “It is simply Mother Nature at work.”

The storm, a rare April northeaster, was described by some on the mainland as the one of the region’s worst in recent memory.

The complex system developed over the Southwest last Thursday, produced thunderstorms and tornadoes in Texas and the Southeast as it made its way across the country, then intensified as it pushed up the Atlantic coast on Sunday.

The center of the storm passed west of the Vineyard on Monday, likely sparing the Island from a worse fate. While Vineyard residents reported minor power outages and some tree damage, much of the East Coast suffered severe flooding. More than eight inches of rain fell in Central Park in New York on Sunday, and winds on Mount Washington in New Hampshire topped 150 miles per hour.

The Vineyard saw a total of 2.5 inches of rain on Sunday and Monday, with winds clocking in above 60 miles per hour. According to data from the Martha’s Vineyard Airport, the barometric pressure fell below 29 inches on Monday morning.

High winds forced the Steamship Authority to cancel the first few ferry trips on Monday. Also during those hours, an emergency Coast Guard helicopter from Air Station Cape Cod airlifted a medical team from Boston to the Martha’s Vineyard Hospital to rescue a newborn in need of advanced medical assistance. The Coast Guard, which provides emergency transportation for Island residents when other means are unavailable, then returned the baby and medical team to a Boston hospital for ongoing care.

It was the high waves coupled with extreme astronomical tides that caused the most damage on the Island. The Martha’s Vineyard Coastal Observatory recorded wave heights over 15 feet, and the moon early this week was unusually close to the Earth, in a new moon phase, and in the same part of the sky as the sun — all factors that strengthen its gravitational pull. The National Weather Service maintained a coastal flood warning throughout Dukes County until Thursday morning.

The large waves on Monday washed over most the south shore barrier beaches — including Edgartown Great Pond, Tisbury Great Pond and the Squibnocket Beach parking lot in Chilmark. Reports of severe erosion extended from Cape Pogue to Aquinnah.

In Edgartown, the breach at Norton Point exposed a buried 52-foot whale that researchers had been unable to locate this winter, and unidentified human remains washed up in Edgartown Harbor on Monday afternoon.

South shore erosion and extreme tides in Katama Bay make up a rare recipe that, when mixed together, will create a breach at Norton Point. Because of a time lag between Nantucket Sound and the Atlantic Ocean, there is often a significant tide differential between Katama Bay and Wasque Point. When the volume of water in the bay becomes so great that the barrier beach can no longer contain it, the strip becomes like quicksand and flows out to sea.

According to Gazette files, significant breaches at Norton Point occurred during violent storms in 1856, 1886, 1938 and 1954. Those breaks lasted an average of about 15 years. Another breach opened for about a year in the late 1970s, and a few other storms have washed out minor breaks. The last one followed Hurricane Bob in 1991, but closed after only a few days.

Watching Norton Point narrow, former Dukes County beach manager Robert Culbert said he expected a breach for the last decade. But the right combination of a severe storm and extreme tides did not take place until this week.

On Norton Point, the breach will likely benefit both surfcasters and shorebirds, as the food being purged out of the harbor attracts fish to the opening, while the washed-over beach provides prime piping plover and tern nesting habitat.

The opening will also likely improve the health of Katama Bay by flushing its shallow waters, and renewing tidal flats for softshell clam habitat.

Meanwhile, the strong currents flowing between Katama Bay and the ocean may pose a challenge to boaters in Edgartown Harbor. Roy Hayes, owner of the Chappaquiddick ferry, described the current yesterday afternoon as roaring through the narrow channel.

“It’s really ripping — probably about six knots of tide,Éd Mr. Hayes said. “This makes our crossing more difficult and time consuming. If it stays open, it will be interesting to see how people get in and out of the harbor this summer.”

Strain on the ferry service will likely be twofold, as the closing of Norton Point also leaves Chappaquiddick residents with only one possible way to get to and from their homes for the foreseeable future.

“It feels kinda weird. Really isolating,” said lifelong Chappaquiddick resident Anthony (Skip) Bettencourt, whose father started the first motorized ferry service from the island in the 1930s.

“But it’s great to be able to see it happen again,” he added, recalling the previous breaches from the 1960s and 1970s. “It’s really exciting.”