Feel like Connecticut has been more humid lately? It’s the dew point

August 30, 2018

Many Connecticut residents may have walked outside from their air-conditioned havens this week and wondered whether it’s ever been this humid this long before.

According to data collected at Connecticut airports by Iowa State University, the state has spent more time at a dew point higher than 70 degrees in 2018 than any other year since the 1990s. Groton data before 1991 was not available.

NBC Connecticut chief meteorologist Ryan Hanrahan noticed the trend this week while looking at data collected at Iowa State for its Iowa Environmental Mesonet website measuring the dew point — the lowest temperature before water vapor becomes fog or precipitation. Higher dew points mean more moisture in the air, which can make high temperatures feel hotter.

The Iowa State record showed the Hartford area has spent more than 620 hours this year with a dew point over 70 degrees, a notable increase over the previous yearly high of 400 hours above that dew point in 2005.

Based on the same Iowa State database, this year is also a record for time spent above the 70 degree dew point in southeastern Connecticut.

“You know it’s been extremely humid, but when you look at the numbers ... it sort of confirms what most people in Connecticut this summer have thought, that ... we can’t really find any summer that’s come close to this in terms of humidity,” he said.

The National Weather Service doesn’t keep a historical archive of dew points, but National Weather Service meteorologist Tim Morrin said this has been a year of high humidity in the region.

“It’s not surprising because we have had some remarkably high dew points,” Morrin said. “Some of the dew points that we’ve seen in our area ... were similar to dew points that you would typically see in the Deep South.”

The dew point on a given day is a more accurate measurement than humidity of how muggy it feels outside, because it takes the air temperature into account — relative humidity can be 100 percent during a blizzard.

“It’s a true measure of the actual water vapor in the air,” said Timothy “You can have a high humidity but not necessarily have any kind of heat stress to the body.”

The National Weather Service says dew points between 55 and 65 can become “sticky” and that dew points start “becoming oppressive” when they’re higher than 65.

“Seventy is when it really starts to get your attention,” Morrin said. “It’s certainly when you start to feel really uncomfortable.”

Morrin said a consistent high pressure system pushing tropical moist air over the Caribbean into the Northeast United States has been causing heat and humidity this summer.

And that consistency — the jet stream pushing hotter air into the northeast all summer without a break — is a symptom of a changing climate, Hanrahan said.

“With climate change, you tend to get stuck into very persistent weather patterns,” he said. “You get week after week after week of the same weather patterns. These kinds of summers, these kinds of extremes are something that’s consistent with a warming world.”


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