Zachary Seamans of Old Orchard Beach cools off with the hose of a cement mixer while working on a foundation in Dayton with temperatures in the mid-90s Monday. “Sun beating on you all day is a lot,” Seamans said. “I’ve been doing it a long time, you get used to it.” Carl D. Walsh/Staff Photographer

Schools in Westbrook, Scarborough, Buxton and beyond sent students home early Monday, and some planned to keep them home Tuesday, as a late spring heat wave raised health and comfort concerns related to wearing masks in poorly ventilated buses and buildings.

Portland and South Portland also opened public buildings to serve as cooling centers for anyone who may need shelter from the heat and humidity, which are expected to intensify Tuesday thanks to a string of sticky nights and record high overnight low temperatures.

Superintendents in Scarborough, Westbrook and School Administrative District 6 sent alerts Sunday night and Monday morning informing their school communities that students would be released by midday Monday. And with temperatures expected to continue in the high 80s and 90s, administrators made plans for remote learning on Tuesday, one of the final days of the 2020-21 school year.

“Our schools have been closed up since Friday, and with the extreme heat conditions that we experienced this weekend, I’m certain that the conditions will only get worse when we add students and staff in addition to another extremely hot day,” SAD 6 Superintendent Paul Penna said Sunday in a district alert. “When you consider the mask requirements in addition to the heat, I’m concerned about the health and safety of our school community.”

Penna said wearing masks to prevent the spread of COVID-19 has compounded the usual challenge of having stuffy buses and inadequate building ventilation during a heat wave. After sending students home on Monday, Penna said, his staff would begin working to modify their lesson plans in preparation for remote learning on Tuesday. SAD 6 includes public schools in Buxton, Hollis, Limington, Standish and Frye Island.

“The weather forecast for Tuesday is still oppressive, so all MSAD 6 schools will be remote tomorrow,” Penna said in a follow-up alert. “The student instructional day will be a half remote day.”

Monday’s preliminary high temperature in Portland was 94 degrees, just shy of the June 7 record of 95 degrees set in 1999, said Maura Casey, a meteorologist with the National Weather Service in Gray.

However, Portland is setting records with stifling overnight lows: Sunday morning the overnight temperature only fell to 68 degrees, exceeding the June 6 record overnight low of 63 degrees set last year; Monday’s preliminary overnight low was 64 degrees, topping the June 7 record of 63 degrees set in 1999; and Tuesday’s overnight low is expected to hover at 69 degrees, far surpassing the June 8 record overnight low of 60 degrees.

Casey said high humidity and short nights near the summer solstice have prevented typical overnight temperature drops that allow buildings to cool off. She said the mugginess would hold on through Monday night into Tuesday, when it will help to push the daytime temperature to 88 degrees, though it will feel much warmer. And again, it likely won’t crack the record high of 90 degrees set in 1999 for June 8. Thunderstorms are likely Tuesday and Wednesday, with the heat and humidity breaking on Thursday, she said.

The Maine Department of Environmental Protection’s Bureau of Air Quality also warned that people should avoid strenuous outdoor activity because the heat is creating ground-level ozone concentrations that are expected to reach unhealthy levels along most of the state’s coastline and the eastern interior of the state.

Faced with daunting forecasts, Scarborough Superintendent Sandy Prince sent an alert Sunday letting the school community know what was on his mind, then followed through and sent students home before noon Monday.

“Given Monday’s heat temperature I will be monitoring the weather knowing we may need to do an early release,” he said Sunday. “I wanted to inform you this evening so that you can plan accordingly if indeed we do have an early release tomorrow. We should be fine for the morning, but by 1:00 the temperatures are scheduled to be in the 90s.”

Prince informed parents Monday afternoon that while temperatures inside Wentworth and Scarborough Middle schools remained in the 70s Monday because they have air conditioning, temperatures inside the primary and high schools soared into the high 80s because they aren’t climate controlled. So on Tuesday, the students at the former schools will attend classes as usual and students at the latter schools will be sent home before noon.

Westbrook Superintendent Peter Lancia said good ventilation systems helped to cool off the city’s schools Sunday night, but he decided to send students home by noon Monday as temperatures crept toward 90 again, and they’ll be learning remotely on Tuesday. Lancia said students, parents and staff have been understanding so far.

“We’re going one day at a time,” Lancia said. “It’s unusual to have this kind of heat this time of year. We knew it would be uncomfortable because people are wearing masks. We certainly wish (the mask mandate) was over with, but we understand why it’s not.”

State and federal health authorities still require public school students and staff members to wear masks indoors, even as mask mandates in other settings have been lifted in the wake of rising vaccination rates and declining case counts.

“Face coverings are required in school settings because the U.S. CDC recommends that those who are not fully vaccinated wear face coverings when close contact with others indoors is possible,” said Robert Long, spokesman for the Maine Center for Disease Control and Prevention.

“Unlike the rest of Maine people, children younger than age 12 have not yet been authorized by the FDA to receive a COVID-19 vaccine,” Long said. “More than 12,000 people under the age of 20 have contracted COVID-19 in Maine. Thus, face coverings are one of the most effective tools for preventing the transmission of the virus among school children.”

Biddeford schools sent students home after lunchtime Monday and promised to send an announcement later about Tuesday’s plans. And Old Orchard Beach Superintendent John Suttie decided Monday that elementary and middle school students in RSU 23 would learn from home on Tuesday.

“OOB (High School) students will still report to school in the morning for their Block 6 and Block 8 final exams and will be dismissed at noon,” Suttie said in a public notice. “The decision to go remote is not an easy one, however, with our students, especially our youngest learners, being in school with a mask in this heat is very difficult and not conducive to learning.”

RSU 23 will resume its regular remote learning schedule Wednesday and return for its final two in-person learning days of the 2020-2021 school year on Thursday and Friday.

Portland opened a cooling center at the Troubh Ice Arena from 9 a.m. to 4 p.m. Monday and plans to do the same on Tuesday. Masks are required inside, according to the city’s announcement. Portland schools already have early dismissals because of the COVID-19 pandemic, said spokeswoman Tess Nacelewicz.

In South Portland, the city opened a cooling center at the municipal community center from 6 a.m. to 9 p.m. Monday and Tuesday, and Superintendent Ken Kunin announced Monday afternoon that the city’s students would be learning from home on Tuesday.

“Temperatures are expected to hit 90 degrees for the third day in a row and tonight it is not supposed to cool down much at all,” Kunin said in an email to the school community. “With almost no air conditioning in our buildings and the requirement for all to wear masks indoors, we have decided that a remote learning day for Tuesday is the most sensible option.”

Kunin apologized for the inconvenience and noted that meals still will be available at all schools from 9:30 to 10:15 a.m. and delivered as usual to Red Bank, Brick Hill and the Quality Inn.

“We look forward to making the best of the final four days of a school year that none of us will soon forget,” Kunin said.