The scene at Coney Island on Saturday was typical for a humid and hot weekend in July: colorful towels, tents and umbrellas packed into the strip of sand.

Along the famed boardwalk in Brooklyn, signs warned visitors of the potential dangers posed by lightning or strong currents, and delineated where and when it was safe to swim.

Yet in one area, closed off by small red flags staked into the sand, a handful of people ventured into the water with no lifeguards present. To the east, where two teenage sisters drowned in the water the night before, swimmers splashed around, unaware or undeterred, enjoying an escape from the city’s heat as temperatures peaked just below 90 degrees.

The sisters who drowned there Friday night, Zainab Mohammed, 17, and Aisha Mohammed, 18, were the second pair of teenagers to drown off New York City’s beaches already this summer. At nearby Jacob Riis Park beach in Queens, two boys, ages 16 and 17, drowned just two weeks earlier. Both incidents happened on especially hot days, after the beaches closed but before the sun had set.

Barely two weeks into summer, the number of drownings off New York City beaches this year has already equaled last year’s total of four and surpassed the previous year’s total of three. One of last year’s drownings happened at Coney Island, when a 15-year-old boy was swept away from shore in a current, according to a database the National Oceanographic and Atmospheric Administration maintains.

In 2019, at least seven people drowned in the Rockaways in Queens. All seven were under 25. The vast majority of drownings, like both incidents this summer, occur when lifeguards are not on duty.

At a closed section of Coney Island, Tamara Priskima was among the beachgoers testing the waters on Saturday with no lifeguard present. She said no one paid attention to the signs telling them to stay out of the ocean.

“I love this water, but it’s no lifeguards here never, never,” Ms. Priskima, 72, said. “I live here two years. I’ve never seen a lifeguard, but a lot of people here.”

For some beachgoers, however, the spate of deaths had made them more cautious about the ocean.

“It’s always been a big issue, and it’s terrifying,” said Angelica Vasquez, 54, who was at the Coney Island beach with her son on Saturday. She added that her children know how to swim, but she did not want to venture too deep. “I refuse,” she said. “They can get their feet wet, that is it. They’re not going in there.”

Ms. Vasquez said she recalled seeing an emergency cellphone alert about the missing swimmers the night before.

“We know we get an alert like that, someone’s not going to be here much longer,” she said.

New York City beaches are staffed with lifeguards until 6 p.m. every day, and swimming is prohibited after that, though that rule is difficult to enforce. When the heat index — a measure of how hot it feels that accounts for humidity — stays high into the night, the cool water can be a tempting respite beyond 6 p.m., especially in the height of summer, when the sun doesn’t set until just before 8:30 p.m.

Last week, the Queens borough president, Donovan Richards, urged the city and the union that represents lifeguards to consider extending the hours that lifeguards are on duty until at least 7 p.m., especially during heat waves.

“We refuse to accept that this is just going to be a normal part of our summer out here in Rockaway and the rest of the city,” Mr. Richards said at a news conference on Wednesday.

The proposal comes as New York is already in the midst of a yearslong lifeguard shortage. Meager staffing has prompted the city’s parks department to close sections of beaches and pools. The city has tried to boost recruitment in recent years, including raising how much lifeguards are paid and making it easier for new lifeguards to get certified, but its efforts still aren’t paying off. This year, the city’s beaches opened with slightly more than half of the 600 lifeguards officials say are needed, according to Gothamist.

Janet Fash, a seasonal chief lifeguard who has worked on New York City beaches since 1979, said that even if the city can’t extend the hours when beaches are open, it should have a skeleton crew of lifeguard trucks with buoys and other rescue devices to patrol the waterline after hours to respond to emergencies.

“If those lifeguards had equipment and binoculars, they could effect the rescue in that window of opportunity, which is typically two minutes,” Ms. Fash said. “That’s where if they’re not on the beach, we don’t advocate anyone else going in the water because a lot of times the hero drowns.”

Earlier this summer, Mayor Eric Adams said he would deploy drones above the city’s beaches, starting around Coney Island. The aerial robots will be piloted remotely and are to be equipped with flotation rafts to drop near struggling swimmers. The program, which has not begun, was billed as a way to augment the lifeguard staffing issues; the city has not said whether the drones will be deployed after beaches are closed.

Some New Yorkers were skeptical.

“Obviously that’s not the answer,” Ms. Fash said. “If there’s a two-minute window of opportunity to rescue someone in the ocean, if they don’t even know what’s occurring, how can they actually effect a rescue?”

The weather on Saturday gave the lifeguards at Coney Island a crowded beach to contend with, along with tricky water conditions. New York City officials issued an extreme heat advisory Saturday, warning that temperatures would crest near 90 degrees and that humidity would make it feel as hot as 100 degrees. Heat like that can be deadly — each summer an average of 350 New Yorkers die from heat.

Meteorologists also predicted that riptides would be likely Saturday, a warning that had been in place Friday, too. A similar forecast had been in effect when the drowning happened at Jacob Riis.

Bjorn Dalin, who lives in Sweden but had lived in New York studying photography, decided to bring his vacationing family to Coney Island because of its lore and the oppressive heat.

“We had to go in the water,” Mr. Dalin, 57, said, noting that he felt safe even though he did not see many lifeguards.

“In Sweden, it’s not common that you have lifeguards at all,” he said. “So you go into the water on your own risk. We watch each other. But we don’t have those tides.”