The warming Gulf of Maine may be making heat waves worse.
In this July 2, 2018, file photo, a man stays hydrated while sunning himself in Portland's Monument Square. Credit: Troy R. Bennett / BDN

Maine’s back-to-back swelters in recent weeks may be a consequence of the warming Gulf of Maine.

Derek Schroeter, a meteorologist with the National Weather Service office in Gray, told Maine Public that the warmer surface temperature in the gulf is a source for humidity.

That’s contributing not only to hot daytime highs, but also to more frequent nights when temperatures don’t fall below 70 degrees Fahrenheit, offering Mainers little relief from the swelter.

“The low temperature [in 2020] didn’t drop below 70 degrees for nine days during the summer. And so usually what that means is, you know, most people are resorting to running their air conditioners at night, as opposed to being able to open up the windows to cool off the house. And a lot of that can be attributed to the Gulf of Maine sea surface temperatures have actually been running well above normal,” Schroeter said.

The Gulf of Maine has been warming faster than most of the world’s oceans, with 2021 being the hottest year on record for the body of water. A new study, published in the journal Communications Earth and Environment, led by Massachusetts-based Woods Hole Oceanographic Institution, co-written by the University of Maine and funded by the National Science Foundation, found that the past century of warming has reversed nearly 900 years of cooling in the Gulf of Maine.

Portland saw temperatures rise to 96 degrees on Sunday, surpassing the previous record of 93 degrees for Aug. 7 set in 2001 and then later tied in 2018.

Bangor saw temperatures rise to 92 degrees on Sunday, the eighth day so far this year when the mercury surged into the 90s.

The weather service station in Caribou tied its record high for Aug. 7 when temperatures hit 89 degrees. It was the 28th day so far this year when temperatures rose above 80 degrees in Caribou.

In Portland, extreme heat has become more common in recent decades, making the city a veritable heat island. In the previous decade, Portland experienced 32 days of extreme heat (defined as a day with a heat index above 90 degrees), compared with six days in the 2000s, nine in the 1990s and three in the 1980s.

That warming trend is likely to continue as the temperatures rise in the Gulf of Maine, Schroeter told Maine Public.