A firefighter cools off while fighting a five-alarm blaze in the Dorchester neighborhood of Boston on Sunday. (Christi Christo/Boston Herald/AP)

It’s the hottest time of the summer in the Northeast, but that doesn’t mean the sweltering conditions haven’t been unseasonably brutal in Boston. The mercury soared as high as 98 degrees while the humidity made it feel up to 10 degrees higher, in what turned out to be the hottest weekend ever recorded in Beantown.

Monday marked the last day of unforgiving highs, but the official heat wave is going down in the books as one to be remembered.

“We don’t see these sorts of heat indexes very often,” said Frank Nocera, a senior meteorologist at the National Weather Service in Boston. “Some places had heat indexes of 105 to 108 degrees.”

Though falling shy of the century mark, Boston Logan International Airport hit 97 Saturday and 98 Sunday. Bradley International Airport in Windsor Locks, Conn., did manage to squeak a 100.

“The last time that happened was seven years ago,” Nocera said. Though it’s the warmest temperature the airport seen since 2012, Sunday’s 100 degrees doesn’t even set a record for the date! It hit 101 degrees in 1991. “It’s definitely hot, but just not quite record-breaking,” Nocera said.


(National Weather Service)

This recent spate of heat wasn’t relegated to just inland areas, though. The blazing air mass charged all the way out to Cape Cod, where the ordinarily moderating marine air succumbed to the sun-baked atmosphere. “They hit 97 degrees in Chatham, which requires a perfect wind fetch to be blowing down the length of the Cape,” Nocera said.

“I’ve been here 20 years, and I’ve never seen this kind of heat make it out there,” he said.

The warmth even reached the 6,288-foot summit of Mount Washington, which set daily record high maximum and minimum temperatures of 67 and 58 degrees Sunday.

What made this weekend’s heat wave particularly memorable were the unusually high dew points, an indicator of humidity, that accompanied the warmth. Humidity more characteristic of a rainforest streamed as far north as the Canadian border, combining with the heat to create dangerous heat indexes. It also prevented overnight lows from dropping much, providing little respite to folks already beleaguered by the harsh weather.

Boston failed to dip below 83 degrees from midnight Sunday morning all the way through Sunday night. That ties the record for the warmest overnight low of any date, last set in August 1975. That’s the average high for this time of year! It also helped maintain Boston at or above 80 degrees for a record-breaking 64 consecutive hours. The previous record stretch was 55 hours.

Boston also managed to set records for its greatest hourly heat indexes between 7 p.m. and midnight.

Parts of New England have seen an unusually high number of hot days this summer. Bradley Airport is already up to 15 days at or above 90 degrees this season, just two shy of the record 17 such days recorded in 2016. There’s a chance Windsor Locks tacks on an additional one or two this upcoming weekend.

Fortunately, there is some relief until then. A line of showers and thunderstorms is set to bring heavy rain and potential gusty winds along the Interstate 95 corridor through Monday evening.

“We’ll have a round [today] and a little more tomorrow morning,” Nocera said. “We’ll cool down a bit and become less humid. It will be pretty comfy.”

But Nocera cautions not to get used to it. “These dew points will come creeping right back up this weekend.”

Heat waves such as this one are becoming more likely to occur, more severe and longer-lasting as the climate warms because of human activities. One of the most robust conclusions of climate science, rooted in statistics and physics, is that, as you increase the global average temperature, the odds of hot extremes increase at a disproportionately high rate.

Andrew Freedman and Jason Samenow contributed to this report.