Dave Epstein

Is this a historically hot summer? Let’s look at the data

The hot summer means the Spray Pool on the Common has often been packed. (DAVID L. RYAN/GLOBE STAFF/FILE)

Is this the hottest summer on record?

The answer depends on where you live and how you measure it.

The bottom line is that this summer will have been one of the hottest summers on record for Boston, much of the interior of New England, and as far north as Caribou, Maine.

Not every weather station in New England will reach this milestone, but many will.

Boston’s been hot

Let’s look at the average temperature period in Boston; as of Sunday morning we were having the hottest summer on record. The period between June 1 and August 31 is considered meteorological summer.

The average temperatures in Boston since June 1, when meteorological summer began. It has been the warmest summer on record so far.

It looks like we’re going to continue the warmer-than-average pattern up through Labor Day. We’re only 1/10th of a degree above the second-hottest meteorological summer on record, but we’re not going to end up with anything but a top five summer in terms of overall temperature.

Northern Maine is having just as steamy of a summer, and it’s highly likely it will end up with its warmest summer on record.

Caribou, Maine, is experiencing its warmest meteorological summer on record.

All that moisture

Another aspect has been the humidity. I looked at how many hours we’ve had in the higher humidity ranges. I started at a 64-degree dew point because once we reach that level and higher, most of us noticed the humidity in the air.

The number of hours at a particular dew point in 2018 (red line) as compared to average (blue line).

What’s worth noting is the number of hours above our average dew point temperatures — for example, the number of hours we experienced a dew point of at least 70 is nearly triple of the average.

It’s the humidity

Let’s take a look at how it’s felt when we’ve combine high temperatures and high dew points. As you can see the number of hours it’s felt over 80 degrees as compared to what is typical is enormous. The blue line represents the average number of hours it would feel a certain temperature, whereas the red line represents the number of hours it’s felt that way this year.

The number of hours at a given heat index in 2018 (red line) compared to average summers (blue line).

Blame the Bermuda high

High pressure off the coast of the United States has been locked in place almost continuously since late June. This has led to a southerly flow of warm, very humid air heading into the region.

Anomolous high pressure will continue off the Atlantic coast into the end of August (Tropical Tidbits)

Is climate change contributing to the record summer? Likely, yes. Before you blame the summer on too much CO2, though, it’s important to remember this would likely have been a very hot summer regardless of the human contribution of anthropogenic gas to the atmosphere. Climate change just makes summers like this more likely to happen and cooler summers less likely.

Summer average temperatures have been increasing as can be seen in this chart from Blue Hill Observatory.

We won’t have all of the data for a couple more weeks and astronomical summer isn’t over for another month, but suffice to say the warm months of 2018 are going into the record books.

Follow Dave Epstein on Twitter @growingwisdom.