The question now: how long will the new opening last?

A storm with blasting southeasterly winds, beginning before sunrise on Sept. 30, sent ocean surf rushing over Norton Point, the barrier beach that has narrowly connected Chappaquiddick to the rest of Martha’s Vineyard since early April.

Later that Wednesday, the tide began to fall on Atlantic side. The beach, softened up by the pounding and flooding it had taken near its eastern end, gave way. Katama Bay, overfull with its own turbulent high tide, rushed through the opening.

There is historical precedent for breach opening and closing several times before final closure. — David Welch

Suddenly Chappaquiddick, severed from the rest of the Vineyard by an opening that had lasted from the spring of 2007 to the spring of this year, found itself cut off once more.

Over the next four days as the gale wore on, the new opening survived strong tides, incoming and outgoing. It appeared to widen each day, especially during high water on the Atlantic side, first to 60 feet, then to a 100, then to 150. Currents rolled chaotically through the waterway, both into the bay and then out to sea. By the weekend, it looked like nothing could gum up the works — the new inlet, it appeared, was going to last for awhile.

“I think when these systems close, the closure is often fairly intermittent and tenuous,” Peter Traykovski of the Applied Ocean Physics and Engineering Department of the Woods Hole Oceanographic Institution, said Monday. “It doesn’t build up a huge sand spit right away. It closes, but the spit is fairly narrow and vulnerable, so there can be another overwash event, temporarily opening it.”

Norton Point broke open during a storm in April of 2007. From a starting place about two miles west of the new channel, the opening migrated eastward over the course of the next eight years until it reached Wasque Point at the southeast corner of Chappaquiddick. The breach closed early in the morning of April 2.

But through the summer the beach remained narrow, low and subject to overwash. The Trustees of Reservations, which manages Norton Point for the county, barred four-wheel-drive vehicles from driving over the most fragile stretch, south of the fishermen’s parking lot on Chappy, through the month of September.

There is historical precedent. A breach that began to close in 1869 reopened several times before it sealed up in the winter of 1870. An opening that occurred in 1886 appears to have taken as much as two years to close permanently at Wasque in 1903. An opening in 1953 took months to close in 1969 and 1970.

It was over the most vulnerable section, 300 yards west of Wasque Point, that the beach dissolved in the gale of last week. Observers, both lay and scientific, were unwilling to guess early this week how long the re-opening might last. Speculation in town and on Chappaquiddick ranged from weeks to months to a year.

Good news for fishermen: bluefish and false albacore have been spotted near opening. — David Welch

But Rick Dwyer, chief ranger for The Trustees, said Monday evening that the deepest water in the new inlet was actually only 15 to 20 feet wide — narrow enough to close within days, he thought, if the currents settled and the wind came around from the south or southwest, encouraging the beach to rebuild. “When high tide comes in, it looks like everything’s underwater,” said Mr. Dwyer. “But it almost looks like sand is being pushed in, and it might want to fill in.”

He said a shoal appeared to be snaking its way from Norton Point into a long channel created by the previous opening, and he hoped this sandbar might either slow the current, helping the inlet to heal, or perhaps build up enough to create a new sand bridge directly to Chappaquiddick. Mr. Dwyer, stationed at the Vineyard end of Norton Point, is no fan of openings; they prevent him from easily reaching The Trustees headquarters at Mytoi Gardens on Chappy.

Mr. Traykovski of Woods Hole studies the waters around Wasque Point. He said Muskeget Channel, a broad, fast-moving waterway east of Chappaquiddick that connects Nantucket Sound and the Atlantic, may speed up the processes affecting the behavior of Norton Point.

“I think that makes the inlet move toward the corner fairly quickly. It still takes seven years or so, but that’s fairly quick, I think, as these inlets go,” the scientist said. “I think it makes the repeat interval of this inlet — opening, migrating, re-closing and doing its whole routine over and over — a little faster than it would be if it weren’t for the big inlet. We still have to do some more detailed studies to find out if that’s true.”

Another issue of concern is erosion. Between 2011 and 2014, tidal processes associated with the last opening clawed away at least 40 acres of bluffs and highlands rising from the southern Chappy shoreline. Two homes were imperiled there. One, belonging to Rick and Jennifer Schifter at Wasque Point, had to be moved back 325 feet from the retreating shoreline in the summer of 2013.

So far there is no evidence that the new opening has caused substantial losses of land along Chappaquiddick, though The Trustees report that the storm ate away sections of the bluffs around Cape Pogue to the north, leaving boulders and rubble on the shoreline, and pushed back East Beach south of the jetties.

Meanwhile, Mr. Dwyer has seen bluefish in the new opening and false albacore near it. Though they must now pay close attention to the tides, overwash and currents ripping through the inlet, surf casters competing in the striped bass and bluefish derby aren’t complaining. “Basically it is what it is. And that’s how most of the fishermen feel about it,” Mr. Dwyer said. “The good thing about most of the fishermen is, they’re going to fish during any adversity at all.”