Southern California’s swampy summer is setting new records, with humidity levels creating conditions that feel more like Florida than the West Coast.
Forecasters attributed the punishing humidity to the remnants of Tropical Storm Iselle moving over the state, as well as unusually warm ocean temperatures due to a combination of a months-long marine heat wave, a powerful El Niño and climate change.
It’s made an intense summer of heat particularly miserable. This week saw new heat records set in some areas, but it’s the humidity that has many at their wits end.
Dew points in the Los Angeles Basin have been “really high,” hovering around 70 degrees in many places, with a few coastal areas like Redondo Beach and Torrance reaching 73 to 75 degrees on Friday, said Ryan Kittell, meteorologist with the National Weather Service in Oxnard. The metric measures the moisture content in the air.
The Orlando International Airport, by comparison, recorded a dew point of 72 degrees Friday afternoon, although that was expected to rise to 75, said meteorologist Melissa Watson of the National Weather Service in Melbourne.
Dew points above 65 degrees are considered to be muggy and somewhat uncomfortable, those above 70 feel very humid and uncomfortable, and those above 75 are oppressive, according to the Weather Service.
Farther south in Imperial County, a weather station along the western shore of the Salton Sea recorded a dew point of 81 degrees Thursday afternoon, according to Gabriel Lojero, a meteorologist with the National Weather Service in Phoenix. That’s “probably one of the higher values” recorded there, but meteorologists don’t have a long period of registered climate data for that area so it’s hard to say, he added. The National Weather Service does not typically keep records of dew points.
The humidity has driven record-high overnight temperatures, with Burbank, Camarillo, Long Beach, the Los Angeles International Airport, Oxnard, Paso Robles, Santa Barbara, Woodland Hills, Anaheim, Santa Ana, Riverside, Big Bear and Idyllwild, among at least a dozen other places, all breaking daily minimum temperature records for the 24-hour period stretching from midnight Thursday to Friday, according to preliminary Weather Service data.
In Palm Springs, the overnight low was 90 degrees, beating a record of 89 set in 2011.
“That’s because water content in the air acts like a blanket that keeps the heat close to the ground, preventing conditions from cooling off at night,” Kittell said. “Believe it or not, water vapor is actually the most potent and efficient greenhouse gas.”
The same is true when it comes to people: Since muggy air can hold less moisture, the sweat on a person’s body doesn’t evaporate as swiftly, which makes it harder to cool off.
The abnormally high overnight temperatures have been exacerbating the risk of heat stress and heat-related illness, said Sam Zuber, meteorologist with the National Weather Service in San Diego.
“We’re not looking at record-breaking high temperatures,” she said. “It’s the overnight lows not cooling off like they should and not giving us a reprieve from the heat in the daytime that are driving heat impacts across Southern California right now.”
The sea surface temperature at the Scripps Pier in La Jolla hit 76.8 degrees Thursday, approaching a daily record of 77 degrees set in 2015.
“Ocean heat waves, just like terrestrial heat waves, have been getting more frequent, more intense and longer lasting” as a result of global climate change, said Alexander Gershunov, a research meteorologist at the Scripps Institution of Oceanography at UC San Diego.
“And when we look at El Nino, it’s a natural pattern, but it’s happening in an unnaturally warming world,” Gershunov said.
The rate at which water evaporates from a wet surface, like the ocean, is controlled by the temperature of the surface, so when the ocean is hotter more water is going to be evaporated from it resulting in higher humidity levels.
“That vapor in the coastal zone is going to make conditions more humid,” Gershunov said. “That’s what’s making our heat waves more humid and that’s what’s keeping temperatures much hotter at night.”
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