‘It’s not the heat, it’s the humidity’ this week

In New England, muggy weather is a given during the summer, and this week we’ll experience of plenty of it.

weather forecast
A man approaches the shore while paddleboarding in Truro. –Craig F. Walker / The Boston Globe

High humidity. If it weren’t so oppressively muggy right now, those two words would be enough send a chill down the spine.

Instead, we’ll have to collectively cringe at the thought of days upon days of uncomfortable air — no matter the temperature — because that’s what’s in store for the region.

What’s happening when ‘it’s not the heat, it’s the humidity’?

Meteorologists use the dew point to measure the amount of moisture in the air. When the dew point is above 60 degrees, most of us notice the feeling of more water vapor in the air. Most people find it quite uncomfortable by the time the dew point reaches the 70s, which Boston usually experiences several times a summer.

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Even if the air temperature is under 80 degrees, it can feel 10 degrees warmer if the dew point is high enough. The chart below shows how much warmer it can feel as the dew point increases.

The heat index
The heat index. —SUNY Albany

How you feel about this is subjective, of course. High humidity generally makes people feel uncomfortable — even at lower temperatures — because it affects the body’s ability to cool itself. All of the moisture in the air slows down the evaporation of sweat on the skin, which would normally keep the body cool.

When high humidity is paired with extreme temperatures, that’s when things get dangerous. The silver lining? I don’t expect that combination for New England this week.

Why? Just why?

Four major types of air masses impact the United States. These different air masses are the key reason the East tends to have more humidity than the West. Maritime tropical air, which is warm and humid and originates in the tropics or sometimes in the Gulf of Mexico, has an easier time flowing northward.

In the Southwest, the dominant air mass is continental tropical, which is warm and dry. Even places like Phoenix, however, can have hot and humid days, but usually it’s just hot and dry.

The four main types of air masses
The four main types of air masses. —NOAA

This week’s forecast: sticky.

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Maritime tropical air will dominate the region’s weather during the next five to seven days. The Bermuda high, a high-pressure system that sits near the island, will continue to pump a southerly flow into the Northeast, bringing moisture our way from the tropics.

the bermuda high
The Bermuda high will impact our weather this week. —COD Weather

This means we’ll have high dew points well into the 60s each day and into the 70s at times. Air temperatures will be in the 80s most of the week, and nighttime temps will hover around 70 degrees. The days will feel like they’re in the 90s when actual temperatures are combined with the humidity. In other words, you can expect to hear people say “it’s not the heat, it’s the humidity” more than a couple of times by the weekend.

This week also brings the risk for showers and thunderstorms. I’m forecasting the greatest threats for precipitation are Monday, Thursday, and Friday.

The humidity will take a break later this weekend.