In a typical year, whatever that means, Boston’s Logan Airport records 14 days of temperatures that are 90 degrees or higher. This year, the number stands at eight, but it’s likely we’ll have two or three more added to the total this week.
In this part of the country, 90-degree weather conjures up thoughts of a heat wave. For many, the number represents the point when it’s just too hot. The funny thing is, it can actually feel more uncomfortable at temperatures under 90, because of the humidity. Check out the chart below, from which you can calculate the heat index. If its 90 degrees and the dew point is under 60, then it only feels like 90. But at 84, with a dew point of 74 degrees, it feels a degree warmer.
In this part of the country, three days or more of 90-degree temperatures amount to a heat wave. The official records for Boston are kept at Logan Airport, which sticks out into Boston Harbor.
A feeble sea breeze of even a few miles per hour can keep Logan from reaching 90, even if it’s 91 or 92 downtown. This fact can make heat-wave headlines very misleading. It will be interesting to see if the airport stays under 90 today, as winds are calm as I write this Monday morning. Calm winds can be a good set-up for an easterly wind later in the day.
The last heat wave at Logan Airport was a prolonged one from July 14th to 20th in 2013. Some inland areas have already seen at least two heat waves this year.
The high-resolution model does a good job of showing where the sea breeze will be this afternoon. The map below, courtesy of WeatherBell Analytics, shows Logan Airport right on the edge of the 90-degree line at 2 p.m.
The Bermuda high pressure off the southeast coast of the United States is going to act like a heat pump for much of this week and bring humid and hot air north. There will be a break in the core of the heat on Thursday, but not before many areas experience five 90-degree days.
This period of the summer will end up as the hottest and most humid part of this year. Most of the summer we haven’t seen an upper-level pattern like the one this week. This prolonged period of humidity is going to make it quite difficult to sleep for the foreseeable future, although we may get used to it as the week goes along.
If you’re on vacation this week, the weather looks wonderful for the beach. If you plan more strenuous activities, you might want to do them early, before the heat is at its worst.
I don’t see any widespread rain or thunderstorms in the forecast, although there could be some showers in isolated pockets on Tuesday and again late in the week or early next weekend. The 90s will break by Thursday, but remember, it’s not going to cool off anytime soon. It will just be less hot.
The global tropical picture remains quite active, but the Atlantic Basin, which would be the source of any local storms, has been quiet. The National Hurricane Center says that one area might organize during the week, but overall, it’s still quiet. The peak of hurricane season won’t arrive until September.