Heat wave likely this week as high pressure builds

By Dave Epstein, The Boston Globe

Some high clouds were streaming north Monday, along with higher humidity, all of which looks to be a precursor to a midweek heat wave.

There could be a little shower Monday afternoon across interior areas and even over northern Massachusetts, but for the most part it’s just a dry, warm day with temperatures well into the 80s.

Another weather system approaches Tuesday with mostly sunny skies but a chance for some building clouds and a pop-up shower or thunderstorm, again mostly away from the coastline. That will be the last chance of rain the rest of the work week.

So far this summer the Bermuda high pressure system has not really exerted itself. This is one of the reasons why we haven’t had much in the way of heat. Over the next few days, high pressure off the Atlantic seaboard will expand toward the coastline and bring a very typical hot and humid flow. Bermuda highs are a very common occurrence in summer and bring about most of our heat waves. As a reminder, a heat wave is three or more days where the high temperature reaches at least 90 degrees. This does not include the humidity, which can make it feel significantly hotter.

Ahead we are looking at perhaps a minimal three-day heat wave Wednesday through Friday with a fourth day on Saturday depending on how quickly a cooler and drier air mass arrives. If you don’t like this kind of weather, there will be at least a temporary pattern change late this weekend when cooler and drier air arrives.

Looking at this summer’s warmth: Although we’ve heard a lot about extreme heat around the globe, locally we haven’t had anything out of the ordinary. As a matter of fact, Boston has only had two days where the temperature has reached 90 degrees at Logan Airport. Inland areas have seen more, with Norwood having eight days so far with a potential to go up to 11 or even 12 by the end of this week.

Although there have been nearly a dozen days considered hot we haven’t had a heat wave in Norwood, and Fitchburg is one of the few places that has experienced an official one this summer. Again this can change this week.

If you don’t like the heat and humidity there’s going to be a bigger change for the second half of the upcoming weekend. Cooler and dryer air from Canada will arrive with dew points at their lowest levels since May for a completely different feeling to the air.