Heat and humidity are most often brought to New England by way of a Bermuda high pressure system off the southeast coast. These weather systems act as a heat pump, throwing hot, humid, and often poor-quality air into much of New England.

Today’s temperatures will easily reach the 90s, with a high likelihood of eclipsing Sunday’s temperatures by 2 to 3 degrees.

The high in Boston reached 92 degrees on Sunday, about 15 degrees above the long-term average and the fourth time we’ve been at the 90 degrees or hotter mark this year. You might have already forgotten, but we had our first three-day consecutive run of 90s in the middle of May, the first heat wave of the year.


And indeed, there is an air quality alert again today. This means if you are someone who suffers from respiratory issues you shouldn’t exert yourself too much. Even healthy individuals can feel the affects of the poor air as it makes it just a bit harder to breath, especially if you are exercising.

In addition to the heat, the air isn’t very clean to start this week.

Tomorrow a cold front will start moving south from eastern Canada and Maine. This will put an end to the heat and humidity for the rest of the week. If Boston reaches 90 before the front passes Tuesday, it would be another heat wave and the sixth 90-degree day this year. To put this in context, the average number of 90 degree days all year is 14, so to have six of them before June 15 is quite remarkable.

I would say there is a 70% chance we reach 90.

Since we started keeping records in Boston in 1872, there have never been two heat waves so early in the season. As the climate continues to warm, it’s like we will see more such hot spells in the coming decades.


On Tuesday night and early Wednesday, cooler air will push south. The loop below shows the falling temperatures throughout Tuesday night setting us up for a much more comfortable Wednesday with low humidity.

I don’t see much in the way of rain with the transition to cooler air. If you have shut off your irrigation system as I have, it’s probably time to flip the switch back to on. Also don’t forget to water those container plants. This heat dries them out quickly.

The weather may turn a bit damp heading into the weekend, but the details on any shower activity will need to wait a few days. I don’t see any more chances of heat waves for a while, however.

You can follow David Epstein on Twitter @growingwisdom.