Department of Health officials reported an average seven-day coronavirus test positivity of 2.8%, moving New York City precariously close to a shutdown of the country's biggest school system and possibly broader restrictions similar to those in March.

Mayor Bill de Blasio has said that he would pause in-person classes should the average positivity go above 3%.

Over the last two weeks, the city's positivity, which measures the share of people testing positive for the virus, has been on a steady upward trend, suggesting that a second coronavirus wave may be inevitable. Friday's data marked the highest the citywide positivity has been since June 8th.

"We’re likely in or coming into a second wave," said Dr. Dustin Duncan, an epidemiologist at Columbia University. He said the reasons experts tend to hedge on calling the latest surge a second wave is because cases could potentially flatten and then tail off.

However, Duncan said he did not see cases diminishing over the next few weeks, citing the cooling weather forcing more people indoors along with the fact that after nine months, New Yorkers have become tired of wearing masks and not seeing their friends and family.

Meanwhile, experts have said that the transmissibility of the virus is expected to peak in January and February.

"It's going to be a long winter," Duncan said.

The average number of new daily cases in the city is now above 900. At one point during the summer, the number of new cases per day had fallen below 200.

During his weekly Friday appearance on The Brian Lehrer Show, the mayor reiterated his commitment to close schools should the positivity rate surpass 3%.

De Blasio said that the city would immediately alert public school families should the rate rise above 3%. Should it happen over the weekend, schools could be closed as early as Monday.

"People should get ready," he said, adding that families should make plans accordingly through at least the end of the month.

About 300,000 students have opted-in to the city's in-person learning program. Ironically, this week was the last period in which families could have switched from the remote-only to hybrid plan.

During his interview, the mayor defended a framework that some experts and parents have described as arbitrary and showing a lack of priorities. It is possible that schools may now be shutdown before indoor dining, an activity that many experts have said is risky and could contribute to virus spread.

Beginning on Friday, bars and restaurants with liquor licenses in New York state will be required to close at 10 p.m. although curbside pickup and delivery can continue. On Thursday, de Blasio said, "Indoor dining is something the state has to make that ultimate decision, obviously. It's an area I've always said we have to look at really, really carefully because of what we've seen around the world."

Evidence that schools have contributed to outbreaks has been relatively scant. According to the latest data, only .18% of 111,852 tests on students and staff have been positive.

Speaking to Lehrer, de Blasio denied that he was bowing down to pressure from the teachers' union by keeping to the 3% trigger despite the testing data and pleas by parents to reconsider.

"It was in effect a social contract," he said.

Once again, the mayor held out hope that the city may still be able to thwart a second wave.

"I think we have a chance to turn things around," he said. "People’s behavior is the biggest element."