For decades, Southern California has been known for its perfect weather. People were drawn to the region with the promise of a mild Mediterranean climate. The weather was marketed by railroads as a remedy for the sick and ideal for agriculture. Rain was infrequent, and umbrellas at events like the Rose Parade were big news. Temperatures could rise, but as boosters liked to say, ‘at least it’s a dry heat.’

Unusual Humidity Levels

This year, however, a significant shift occurred. The humidity in Southern California’s air has felt more akin to Florida and the Gulf Coast. Many have described it as the worst they’ve ever experienced. Scientists link the high heat and tropical air mass as causing unprecedented humidity. UC climate scientist Daniel Swain notes that evidence suggests this summer has been the most humid on record for parts of Southern California.

Swain warned that this could be a grim preview of future conditions. Southern California has been facing rising temperatures due to climate change. This change has increased the risks of fire and droughts. A strong El Niño is expected this winter, potentially causing severe damage along the California coast.

“In some cases, engineering solutions to avoid serious coastal flooding and erosion may be impossible,” Swain stated.

Record-Breaking Dew Points

Swain had already calculated, before this week’s extreme humidity, that this summer reached a dew point level measuring the highest humidity since 1980. The data, sourced from airports in Santa Barbara, Los Angeles, Long Beach, and San Diego, confirms this finding.

The National Weather Service provides dew point benchmarks: below 60 degrees is comfortable, above 65 is muggy, over 70 is very humid, and surpassing 75 is oppressive. This week, Long Beach, Huntington Beach, and Newport Beach reached a dew point of 76, akin to levels in New Orleans and Orlando, Florida.

Effects on the Local Climate

Several factors contribute to Southern California’s usual mild summer climate. They include cool ocean effects, protective mountains, and typical weather patterns that avoid drawing in tropical moisture. Typically, land-to-sea and sea-to-land breezes moderate the temperatures. Meteorologist Kristan Lund explains that these cycles bring dry air from deserts in the morning and cool ocean air in the afternoon.

Historically, high pressure results in warm, dry weather that does not attract tropical moisture. Southern California’s ocean water is much cooler compared to the Gulf and East Coasts, influencing its typical low humidity.

This summer, these protective mechanisms failed dramatically. The region saw elevated humidity levels, disrupting the usual dry heat. Swain noted that high heat-index values have been especially noticeable in Los Angeles, where many lack air conditioning. This combination poses severe health risks such as heat stroke and heat exhaustion.

Understanding the Causes

The remnants of Hurricane Marie, part of an active hurricane season in the eastern Pacific Ocean, contributed to the extreme humidity. Marie funneled moisture over the area, introducing tropical conditions. This moisture combined with monsoonal moisture from the southeast worsened the region’s heat and humidity.

An extraordinary marine heat wave, tracked by the National Oceanic and Atmospheric Administration (NOAA), has also intensified the situation. Warm ocean waters stretch from the Galápagos to Alaska, with off-the-charts temperatures near Baja California.

“The water off California is at or above the highest-ever observed levels, contributing to the heat,” Swain commented.

Looking Ahead

The prolonged effects of these conditions could continue. Future waves of humidity are likely, and not the most extreme event of this decade, according to Swain. Coastal Southern California risks significant damage due to large waves and high tides, worsened by rising sea levels and possibly concurrent weather events like Kelvin waves, which are expected in the coming months.

Swain expressed concern for potential impacts in November, December, and January. Super king tides anticipated during these months could exacerbate coastal flooding and erosion.

The ongoing increase in ocean warmth, driven by human-caused global warming, raises sea levels. This is influenced by the melting of continental ice sheets. Swain highlighted a concern that coastal flooding events are being impacted by melting in Greenland and Antarctica over recent decades.