If you watch the news or follow the weather at all, chances are you’ve heard of the Bermuda high. Meteorologically, the Bermuda high is really an extension of the Azores high — a quasi-permanent ridge of high pressure that oscillates in strength and position over the North Atlantic Ocean. During the summer months, the ridge shifts north and westward and positions itself over the western Atlantic — very near the island of Bermuda, where it becomes a prominent player in our summer weather.
Because winds flow clockwise around areas of high pressure, the Bermuda high promotes a warm, southwesterly flow of air up the Eastern Seaboard. At times, the ridge flexes far to the north and west, bringing us periods of hot weather and humidity that seem tropical. On occasion, the Bermuda high will weaken, and a frontal zone will drop into our region, allowing for interludes of cooler weather. But as we move deeper into July, those intrusions of cooler and drier air become less frequent, and the Bermuda high reaches its climatological maximum strength.
Meanwhile, by mid-July our near-shore water temperatures have recovered from their seasonal nadir. Long gone are the ice-cold 30s and 40s of early spring. The buoy in the heart of Cape Cod Bay reads about 64º F right now, meaning the shallow near-shore waters are in the 70s and will continue to warm into August. The Nantucket Sound buoy is already reading 73º. No longer does a wind off the water guarantee a chilly day; instead, something new starts to happen: eternal humidity.
From now until mid to late August it is quite difficult for the atmosphere to dry out. In addition to contending with the strength of the Bermuda high and the humid southwest flow of air, the local water temperatures act as a humidifier — keeping dewpoint values in the 60s and 70s almost nonstop. This has become increasingly noticeable over the last two decades, and the data confirm it.
In Hyannis between 1975 and 1995, just two years had 40 or more days with a dewpoint reading at or above 70º. Between 1995 and 2025, that was the case in 15 years. In Provincetown, where the data date back only to 1988, there wasn’t a year that recorded 40 or more days with a dewpoint over 70º until 2010. Since then, 8 years have had 40 or more such days. So, not only are our summers getting warmer but they are getting more humid, too.
While the early week sultry conditions have relaxed some, don’t expect any prolonged relief from the humidity. Dewpoint values are likely to remain elevated through the weekend and into next week.
