Record-Setting Humidity Grips Eastern United States This Summer

Published Time: 08-11-2025, 15:00

The summer of 2025 has proven to be the muggiest on record for more than 70 million Americans living east of the Rocky Mountains, marking a significant shift in the region’s climate patterns. Recent data analysis by the Associated Press highlights an alarming rise in humidity levels, linked to ongoing climate change. This increase in moisture has brought not only discomfort but also health concerns, especially as nighttime temperatures remain unusually warm, limiting relief from the heat.

Unprecedented Humidity Levels Across 27 States and Washington, D.C.

According to data from the Copernicus Climate Service analyzed by the AP, parts of 27 states along with Washington, D.C., experienced a record number of days in June and July with average daily dew points at or above 65 degrees Fahrenheit. Meteorologists define dew point as the temperature at which air becomes saturated with moisture, and it is considered the most reliable measure of humidity. Dew points at or above 65 degrees indicate conditions many find uncomfortable, especially during the warmer months.

Even more striking, during peak hours, dew points often soared to nearly tropical levels. Cities such as Philadelphia recorded 29 days, Washington D.C. 27 days, and Baltimore 24 days with peak dew points reaching 75 degrees or higher—values described by the National Weather Service’s Tampa office as “oppressive.”

Rising Dew Points Signal Increasing Heat Stress

The AP’s calculations reveal that dew points this summer averaged at least six degrees Fahrenheit higher than the 1951–2020 historical norms in major cities including Washington, Baltimore, Pittsburgh, Richmond, Columbus, and St. Louis. Overall, the average dew point for the entire eastern half of the country surpassed 66 degrees this summer — the highest since records began in 1950.

“This has been a very muggy summer. The humid heat has been way up,” said Bernadette Woods Placky, chief meteorologist at Climate Central. The combination of heat and humidity is particularly taxing on health, intensifying the effects of high temperatures.

Extreme Humidity Days Becoming More Frequent and Widespread

Cameron Lee, a climate scientist and humidity specialist at Kent State University, noted that he personally recorded dew points as high as 82 degrees at his Ohio weather station twice this summer—levels that exceed typical meteorological charts.

“Not only are average humidity levels rising, but extreme humid days are becoming more frequent and cover more geographic areas,” Lee said. He emphasized that these super sticky days, once rare, now occur repeatedly each summer, impacting daily life for many Americans.

The Impact of Sticky Nights on Health and Comfort

Humidity’s influence is especially pronounced during nighttime. High moisture levels prevent air temperatures from cooling down after sunset, leading to dangerously warm overnight lows. According to Zack Taylor, forecast operations chief at the National Weather Service’s Weather Prediction Center, numerous cities have set records for highest minimum temperatures this summer.

Raleigh, Charlotte, Nashville, Virginia Beach, and Wilmington broke overnight heat records, while New York City, Columbus, Atlanta, Richmond, Knoxville, and Concord came close to doing so. “What really impacts the body is that nighttime temperature,” Taylor said. “Without adequate cooling at night, the body cannot recover from daytime heat, increasing health risks, especially for those without air conditioning or cooling centers.”

Climate Change’s Role in Amplifying Humidity and Heat

Meteorologists and climate experts agree that the rising humidity is partly due to climate change driven by the burning of fossil fuels such as coal, oil, and natural gas. The eastern U.S. has seen an average increase of approximately 2.5 degrees Fahrenheit in summer dew points since 1950, according to the AP’s analysis of Copernicus data.

Historically, the eastern half of the country had average dew points in the low 60s during the summer—considered noticeable but generally comfortable. However, in four of the past six years, the average dew point has hovered at or above 65 degrees, crossing into uncomfortable territory.

Lee remarked on the significance of this trend: “This is a massive increase over a relatively short period of time.” Small rises in average dew points translate into more frequent extreme humidity days, which have tangible effects on public health and comfort.

The Science Behind Rising Humidity and Heat

The relationship between heat and humidity follows a fundamental principle of physics: the atmosphere can hold approximately 4% more water vapor for every degree Fahrenheit the temperature increases (or 7% for every degree Celsius). This feedback loop means warmer air leads to higher humidity, which in turn amplifies the perception and impact of heat.

Throughout much of the summer, high-pressure systems entrenched over the Midwest and Eastern U.S. drove temperatures upward, while persistent, above-average rainfall added moisture to the atmosphere. The absence of strong cold fronts that typically relieve heat waves prolonged these sticky conditions until August brought some respite.

Shifting Humidity Patterns Across the U.S.

While humidity has traditionally been concentrated in the southern states, experts note that uncomfortable dew points are now increasingly common further north. University of Georgia meteorology professor Marshall Shepherd explained, “Summers now are not your grandparents’ summers.” The movement of muggy conditions into northern regions poses new challenges for residents less acclimated to high humidity.

Preparing for a More Humid Future

With climate change continuing to push dew points higher, residents, urban planners, and health officials across the eastern U.S. are urged to prepare for hotter, stickier summers. The combination of rising heat and humidity increases the risk of heat-related illnesses and strains infrastructure and energy systems.

Public awareness and access to cooling resources remain critical as the frequency of oppressive summer days grows. Understanding the role of dew point as a key humidity metric can help communities better communicate heat risks and improve response strategies.