LA Swelters: Why This Summer's Heat Feels Worse Than The Forecast

The discrepancy between reported temperatures and the actual sensation of heat is primarily due to two factors: unusually warm nights and elevated humidity. Daniel Swain, a climate scientist and associate researcher at University of California Agriculture and Natural Resources, commented that this summer's discomfort has been driven less by scorching afternoons and more by "record-warm nights and Miami-level humidity." He observed that while daytime temperatures in some areas have been near or slightly above average, overnight minimum temperatures have been "very far above average across nearly all of the state," effectively depriving the human body of a crucial recovery window during cooler hours.

Medical anthropologist Bharat Venkat, director of the UCLA Heat Lab, further explained the role of humidity. He stated, "Sweating is the most powerful mechanism our body has at its disposal to cool us down." However, muggy air holds less moisture, which hinders the evaporation of sweat from the skin, making the heat feel significantly more intense. Meteorologist Tom Kines of AccuWeather Inc. corroborated this, noting that when downtown Los Angeles neared 90 degrees Fahrenheit, factoring in dew points made it "feeling like four to eight degrees higher than the actual temperature." The National Weather Service uses the term "heat index" to describe this "feels like" temperature, while AccuWeather refers to it as "RealFeel." Reports indicate that a temperature of 90 degrees Fahrenheit with 60% relative humidity can feel like 100 degrees Fahrenheit.

The elevated humidity itself is a consequence of unusually warm ocean temperatures along the Southern California coast, a condition that has persisted for most of the summer. This marine heat wave, extending across the Pacific from Mexico toward Hawaii, is warming the waters off Southern California, leading to increased moisture evaporation into the atmosphere. A weak onshore flow then carries this humidity inland, particularly at night, contributing to the elevated overnight readings. Daniel Cayan, a climate researcher at Scripps Institution of Oceanography at UC San Diego, attributed the unusual ocean warmth to a weather pattern over the past three months, characterized by abundant sunshine heating surface water and light winds preventing mixing with cooler water below.

Jennifer Francis, a senior scientist at the Woodwell Climate Research Center, remarked that "This marine heat wave has fingerprints of human-caused climate change all over it." She added that while the humidity "isn't sticky by East Coast standards, but it's enough to make temperatures in the high 80s feel like the low 90s, which folks in LA are not used to." Bryan Lewis, a National Weather Service meteorologist in Oxnard, also pointed out that remnants of Tropical Storm Elida and Hurricane Fausto have pushed tropical moisture into the area. Additionally, a strong high-pressure system over the southwestern U.S. is largely responsible for the heatwaves, with offshore winds blocking the ocean's usual cooling effect. Ryan Kittell, a meteorologist with the National Weather Service in Oxnard, explained that this high pressure brings "compressional warming."

In response to the severe heat, public figures and organizations have issued numerous warnings and advice. The National Weather Service has released multiple extreme heat warnings, advisories, and watches across the region. Air quality officials have issued an advisory for high ozone pollution, a condition exacerbated by the heatwave. The Los Angeles County Department of Public Health has provided warnings about dangerous triple-digit temperatures and offered tips to prevent heat-related illness, urging residents to stay hydrated, seek air-conditioned spaces, and check on vulnerable neighbors. Dr. Muntu Davis of the department has stressed the importance of these precautions.

The ongoing heatwave underscores the growing challenges posed by changing climate patterns, particularly for regions not traditionally accustomed to such prolonged and humid conditions. The combination of scorching days and stifling nights creates a significant public health risk, making it crucial for residents to heed official warnings and take proactive measures to protect themselves and their communities. As the region continues to experience these unprecedented conditions, understanding the science behind the "feels like" temperature becomes vital for public safety and preparedness.