Across Los Angeles, at festivals, botanical gardens and even the beach, the heat is the hottest topic. Residents lament astronomical electricity bills or lack of air conditioning. Memes about the swelter multiply. Neck fans abound. Weather is often the easiest small talk in a region whose normal summers offer pleasing aridity and cool nights. But this year, there’s a disquieting debate: Is humidity making things worse? Meteorologists don’t track humidity as closely as temperature, but trends point to stickier air than usual in Southern California, from San Diego to Santa Barbara. That’s in part because the rapidly warming Pacific Ocean off the coast feels like a bath tub.

Dew points — the measure of water vapor in the air — have nudged slightly higher than average much of the summer. The higher the dew point, the more humid it feels, the frizzier the hair, the more stubborn the sweat stain. The human body experiences heat more intensely, fighting to cool itself as perspiration becomes less efficient. “This is why humid heat waves are so oppressive compared to dry heat waves,” said Alexander Gershunov, a research meteorologist at the Scripps Institution of Oceanography.

For others, one major change has been mosquitoes, which thrive in more humid climates but have historically been less omnipresent. This summer, friends have been warning one another to break out the DEET. West Nile virus activity across the state is at a five-year high. Two factors are driving up dew points, according to Ryan Kittell, a meteorologist with the National Weather Service office in Oxnard, Calif. Winds are pulling moist tropical air from Mexico, and the Pacific Ocean off the coast has been five to 10 degrees above normal.

The marine heat wave that started in February is expected to be exacerbated by the El Niño weather pattern, and “cause it to persist into fall and winter, and even into next spring,” said Art Miller, a research oceanographer emeritus at the Scripps Institution. In coming days, much of the region is expected to record the summer’s hottest temperatures, while moisture from a tropical storm simultaneously flows north. Los Angeles officials said the heat will be dangerous and have issued an emergency alert.