Southern California experiences record humidity amid tropical moisture and warm ocean waters
Scientists say this summer's dew points were the highest in 46 years, driven by remnants of Hurricane Marie, an El Niño pattern and unusually warm Pacific waters.
Southern California recorded unprecedented humidity this summer, with dew points reaching 76 °F at several coastal stations, levels comparable to those in New Orleans and Orlando. UC climate scientist Daniel Swain said the region is experiencing "some of the highest humidities we’ve ever experienced in coastal Southern California" and that the summer may be the most humid on record for parts of the area.
The surge in moisture is linked to the remnants of Hurricane Marie, which transported tropical moisture into the region, and to monsoonal flow from the southeast. Meteorologist Kristan Lund noted that Marie "was able to funnel its moisture over our area from the southwest, and that brought more humid conditions because it’s tropical moisture." The humid air combined with an extraordinary marine heat wave, with sea-surface temperatures off Baja and the California coast up to 10 °F above average.
Normally, coastal Southern California benefits from cool ocean breezes, mountain barriers and high-pressure patterns that keep tropical moisture at bay. This summer those safeguards broke down, leading to heat-index values that exceed historic observations, especially in central and south-central Los Angeles where many homes lack air conditioning.
Los Angeles County health officials warned residents to watch for heat-related illness, emphasizing that heat causes more deaths in the United States than floods, storms and lightning combined. Dr. Muntu Davis said older adults, young children, outdoor workers and people with chronic conditions are most vulnerable.
Experts caution that the current conditions may foreshadow more extreme weather later in the year. Swain highlighted the risk of coastal flooding, beach erosion and bluff collapses as sea levels sit six to ten inches above average and additional Kelvin waves—warm water disturbances associated with strong El Niño events—are expected through the winter. He warned that "the reality is, in some of these cases, we may not be able to do much at this point to engineer a way out of quite-serious coastal flooding".