Andy Cohen, Fran Lebowitz and Others Gather for Little Island Performance

“It’s a miracle on the water,” the actress Candice Bergen said, gazing at a grove of trees on Thursday evening as she took shelter from the sun beneath a canopy.

It was the opening night of the summer performance season at Little Island, the three-year-old floating park built on a reconstructed pier in the Hudson River.

Despite thunderstorms earlier in the afternoon, around 700 actors, designers and media moguls turned up under a smattering of canopies near the island’s amphitheater, among them Andy Cohen, the Bravo host and executive producer; Annie Leibovitz, the photographer; Fran Lebowitz, the writer; Natasha Lyonne, the actress; Bryan Lourd, the chief executive of the talent agency CAA; and Jason Blum, the film producer.

As waiters ferried watermelon spears and cartons of boxed water on silver platters, attendees trickled into the glade over twin gangways on the north and south sides of the island.

“It reminds me of paradise,” said Mr. Blum, whose film and television production company, Blumhouse, is known for movies like “M3gan” and “Get Out.” He wore a lilac dress shirt and navy trousers — the dress code, per the invitation, was “casually fabulous.”

The crowd was there for the buzzy world premiere of a dance-and-musical hybrid piece, “How Long Blues,” that was conceived, choreographed and directed by Twyla Tharp. It is the first full-length new work in a decade from the choreographer, and performances run through June 23.

Ms. Tharp said that the piece’s expressiveness and abrupt shifts in situation and tone matched the fluid weather conditions at the park’s 687-seat outdoor amphitheater.

“You step over a boundary between life and art on that stage,” Ms. Tharp, 82, said of the piece, an epic narrative on the theme of resilience inspired by American jazz and the writing of Albert Camus, with original music and arrangements by T Bone Burnett and David Mansfield.

Fortunately, this June night was more balmy than tempestuous. Little Island, the billionaire media mogul Barry Diller’s $260 million, 2.4-acre dream project that gestated for seven years, and which was delayed by legal challenges before finally opening in 2021, does not come equipped with a clear rain plan.

It has plenty of other perks, though: shady, 35-foot trees; a secret garden; dozens of overlooks where visitors can watch performances in the amphitheater at no cost (seats are $25), a prime vantage point for a riverside sunset over Hoboken.

Mr. Diller, who with his wife, the fashion designer Diane von Furstenberg, largely funded the park’s construction, has committed to spending more than $100 million over the next two decades on programming. The venue has more than 100 dance, music, theater and opera performances scheduled over the next four months — many of them world premieres.

Thursday night, though, was about soaking in the only-in-New York lineup. As the sun slowly sank behind the gently lapping waves, a group of 26 dancers, singers and musicians that included the Tony Award-winning actor Michael Cerveris, along with Tharp regulars like John Selya and Reed Tankersley, carried out a vague pantomime in the midst of energetic dancers.

Ms. Lebowitz, in her standard blazer and jeans, clutched a black umbrella and bopped her head in time to Frank Sinatra’s “My Way” during the performance. Mr. Cohen, who was seated next to Jane S. Buffett, Jimmy Buffett’s widow, tapped his foot.

About 30 minutes into the performance, the wind picked up, and drops of rain sent people reaching for their jackets. Mr. Cohen eyed the sky warily, but the rain never moved beyond a sprinkle.

After the hourlong showcase, attendees trickled down to an after-party on the lawn as ushers handed out blue ponchos. They clustered under canopies lit by red, blue and yellow lights, though the rain soon let up and the weather reverted to a gentle breeze.

People sat on blankets on the lawn amid lanterns, sipping wine and snacking on plantains and almonds. Ms. Lebowitz hugged Mr. Diller and Ms. von Furstenberg.

“Thank you, Barry, for a wonderful evening,” she told him.

Mr. Diller congratulated Ms. Tharp.

“It was a little scary with the velocity of the wind and the density of the rain,” she said, “but we made it.”

Mr. Cohen talked with Ms. von Furstenberg’s son, Prince Alexander von Furstenberg, who had flown in from Los Angeles for the occasion, as well as the premiere of the new documentary about his mother, “Diane von Furstenberg: Woman in Charge,” at the Tribeca Film Festival the night before.

“You have to respect it,” Mr. von Furstenberg said of the ambition to build Little Island. “They had a dream and they made it happen. And it’s not cheap.”