Children play in a fountain on the Rose Kennedy Greenway as temperatures rose into the high 90s with a heat index close to 105 in Boston on Wednesday. (John Cetrino/EPA-EFE/REX)

From Boston to Hartford and Albany to Portland, population centers in the Northeast United States have staggered through unheard of humidity levels in the summer. August has been unforgiving, almost from start to finish.

For long stretches, the moisture-laden air over the region has felt more like Florida, as if you could cut it with a knife.

“It’s been relentless,” said Ryan Hanrahan, chief meteorologist at the NBC affiliate in Hartford. “Almost nonstop high humidity.”

Humidity is one of those weather attributes that’s hard to love, but drawn in off the abnormally warm Atlantic Ocean, it has come in prodigious quantities over a region that usually gets it in much smaller doses.

Meteorologists evaluate the amount of moisture in the air using the dew point, which is the temperature at which the air would need to cool to reach saturation. Anytime the dew point exceeds 70 degrees, it is very muggy outside.

“The amount of time we’ve spent with a dew point greater than 70 degrees this year is outrageous,” Hanrahan tweeted. “More than 600 hours just blowing away the previous records for most humid summer.”

Data from the Iowa Environmental Mesonet show several other cities in the Northeast have witnessed such humidity levels for record-challenging duration, including Albany, Boston, Burlington, Portland and Providence.

In the Mid-Atlantic, including the Washington area, it has been more humid than normal but not as extreme, compared with locations farther north. Moreover, the Mid-Atlantic, especially east of the mountains, is more used to persistently high humidity in the summer. That said, Washington’s Dulles Airport is witnessing one of its most humid Augusts on record.

Abnormally warm water and nighttime temperatures

Sea surface temperature anomalies show much of the western Atlantic in above-normal conditions. (

Hanrahan linked the high humidity levels to above-normal ocean temperatures at the coast and farther offshore. He pointed out that the surf temperature in New Haven Harbor, in Long Island Sound, is a whopping 83 degrees. Some of the warmest water temperatures relative to normal are just offshore of New England in the Western Atlantic.

Warmer water leads to more efficient evaporation and, ultimately, more moisture in the air. Stagnant areas of high pressure have helped hold the steamy air in place.

High pressure has prevailed for most of the summer across the Northeast. The high pressure zones have focused near the Canadian border and over the open waters of the North Atlantic. This positioning has allowed a fetch of wind to come off the warm waters in a consistent manner.

The abundant moisture in the air has been reflected in unusually high nighttime temperatures. They are the best indicators for the extraordinary humidity levels, said Eric Fisher, chief meteorologist for Boston’s CBS affiliate. Boston witnessed its highest average overnight low temperature on record in the summer, he said.

High moisture content in the air keeps temperatures from falling as far as they otherwise would at night. Throughout August — and much of the warm season — the Northeast has kept cooking at night, when it usually cools.

Low-temperature anomalies for August. (

In the above map, the vast majority of the region covered by the deep orange blob in the Northeast has seen overnight lows that rank in the top five warmest in the modern record during August, with most ranking either No. 1 or 2.

Feeling like another place

The Northeast Regional Climate Center features on its website a database that finds the best match between the weather happening at a particular place and the part of the country where such conditions are normally most common.

The database reveals that much of Southern New England has felt more like the coastal Mid-Atlantic and Southeast Virginia for the past month or so. Hartford’s conditions have mostly closely resembled Baltimore. Boston’s best match has been Norfolk.

How it has felt across the Northeast this past month. (Northeast Regional Climate Center, modified by CWG)

Unsurprisingly, with all the moisture in the air, it has also been rather wet. Hartford is having its seventh-warmest and eighth-wettest summer, Hanrahan said.

While it’s easy to complain about the humidity, plentiful soil moisture and abundant plant life are positive attributes.

At least a little more ahead

With the prospect of high pressure building in again next week following a brief “respite,” more records are set to fall or be further demolished.

Around Boston, Fisher is keeping tabs on a number of them.

Boston and nearby locations are also seeing historic numbers of those warm nights with low temperatures at or above 70 degrees. “Providence and Blue Hill Observatory have already broken their annual records, and Boston should tie today [Thursday], then break the tie next week,” Fisher said.

Temperature forecast for Hartford, Conn., from the European model. Note the temperatures next week may be more 90-plus days than the 80s. It does, however, show something of a turn toward cooler weather. (

High temperatures next week are forecast to reach at least the upper 80s in Boston, but, as time wears on, 70s are destined to become more prevalent, as they tend to do as the calendar moves through September. Mercifully, it is likely that 90-degree days and crazy-warm nights are just about done.

The humidity experienced in the Northeast in the summer is likely to become more frequent and intense in the coming decades, as its climate warms and moisture levels further increase.