LI set a record for humidity in June, and July is shaping up to be even worse, forecasters say

Sorry, Long Islanders: July could be even muggier than June, when the humidity was almost double the record set in 2005.

The first half of July "has continued the sultry summer conditions that June introduced," said Dominic Ramunni, a National Weather Service meteorologist based in Upton.

Just how humid the rest of the Summer of 2021 might be on Long Island is pretty much anyone’s guess, meteorologists say, as long-term forecasts often are imprecise at best.

"We don’t have a good, firm handle on why these patterns become established," said David Robinson, the New Jersey state climatologist who manages the Rutgers New Jersey Weather Network, in a phone interview.

But climate change is one of the reasons humidity is rising, experts say, as well as causing more powerful storms, heat waves and droughts.

Historic spike

Humidity is measured through dew points, which are reached when the air cools down enough for vapors to condense. This happens, for example, when someone blows on a mirror.

When dew points are below 55 degrees, it will feel "dry and comfortable," according to the National Oceanic and Atmospheric Administration. From 55 to 65, NOAA says, it will feel sticky or muggy, and at 65 and above, it becomes "oppressive."

The weather service’s dew point records for Long Island began in 1973. Until now, June 2005 held the previous record of 90 hours with dew points at or above 70 degrees.

"We blew that away this June with 169 hours," Ramunni said.

Then from July 1 to July 15, the dew point in Islip hit or surpassed 70 degrees for 171 hours — or just over seven straight days, Ramunni said.

The monthly average for July is 195 hours, or about eight days.

"So we are approaching our monthly average with half of the month remaining," Ramunni said.

The historic spike in June’s dew point was first spotted by Josh Timlin, an earth science teacher at North Shore High School, though his estimate was slightly lower at 155 hours.

"I do kind of keep tabs on the weather," said Timlin, who enjoys uncovering how a pattern or development he spots "fits into the context of longer-term trends."

Clouds, which develop when the air holds as much water vapor as possible, are another indicator of humidity.

So far, Timlin said his records show that July is notable for its cloud cover. By his calculations, there have so far been 187 hours of clouds, more than double the monthly average of 84 — and exceeding the next highest total of 166 set in 1990.

The weather service did not immediately comment on Timlin’s analysis, which he said is based on hourly data from Long Island MacArthur Airport in Ronkonkoma.

This summer’s oppressive humidity, blowing off a warming Atlantic Ocean and Gulf of Mexico, has been a keen contrast with the West Coast’s remarkably arid heat wave still carving countless new high temperature records.

This week should offer some relief with drier air sweeping in, though perhaps not as much as Long Islanders are hoping for.

"It’s a little bit of a break, maybe not quite the late summer/fall air maybe some folks are looking forward to now," said David Radell, a weather service meteorologist based in Upton, by telephone.

The high pressure system that will trim the Island’s humidity early this week, as its falling air dries and cools, will be partly offset by temperatures expected to cling to the upper 80s and even low 90s, Radell said.

And the odds of precipitation were estimated at around 33% from Thursday to the following Monday by the weather service’s Climate Prediction Center.

Why so much humidity now?

High pressure systems spin clockwise, so when one of them, called the Bermuda High, hovers around the resort island in the summer and autumn, it can draw the warm and moist air north from the Gulf of Mexico and along the Eastern Seaboard.

"We kind of have this highway from the surface to the mid-atmosphere of very strong southwesterly flow, and it’s bringing a lot of moisture," said Mark William Wysocki, a senior lecturer of Earth and atmospheric sciences at Cornell University and New York State’s climatologist.

Climate change is raising air and ocean temperatures around the world, so in the tristate area, increasing evaporation off both the Gulf of Mexico and the Atlantic Ocean is sending the humidity higher as warmer air carries more moisture.

Said Robinson, the New Jersey climatologist: "And of course, Long Island is right in line to get that moisture."

Depending on where it drifts, the Bermuda High can also help direct storms and hurricanes toward the western or eastern Gulf coast.

Fortunately, the Bermuda High won’t stick around forever: In winter and the early spring, this semi-permanent high pressure system’s influence on U.S. weather wanes as it heads to the Azores, more than 2,000 miles east of Bermuda.