Four California tide gauges reach their highest observed water levels
Four California tide gauges registered their highest observed water levels during late October, when flooding inundated low-lying coastal communities. Exceptionally high astronomical tides, warm-water waves associated with El Niño and a marine heatwave contributed to the elevated water. The four stations were San Diego, La Jolla, Los Angeles and Santa Barbara.
Science··Morning
October flooding brings record readings
Water levels measured at Los Angeles and San Diego in California reached record heights during October’s coastal flooding.[1], [2]
The US National Oceanic and Atmospheric Administration (NOAA)’s 4 November assessment identified four stations with their highest observed levels between 24 and 30 October: San Diego, La Jolla, Los Angeles and Santa Barbara. Some California tide-gauge observations extend back more than a century. Low-lying communities experienced inundated roads, homes and businesses as elevated water spread inland. The measurements describe water above each station’s local tidal reference, allowing the assessment to compare the event with earlier observations at the same location.[1]
A local tidal baseline
NOAA expressed the heights relative to Mean Higher High Water, the average of the higher high tides at a location. Rounded to metric units, San Diego reached about 85 centimetres above that baseline, Los Angeles about 82 centimetres, and La Jolla and Santa Barbara about 81 centimetres each. San Diego’s highest level was measured on 27 October. Other stations also entered their ten highest observations: Santa Monica reached second place, Port San Luis fourth and Monterey seventh. The assessment includes both all-time local records and unusually high readings that remained below an earlier local peak. Each station uses its own local tidal baseline, so heights are compared against its own observation history.[1]
Warm water added to unusually high tides
The agency attributed the flooding to several coinciding processes. The Moon was full and near its closest point to Earth, producing a perigean spring tide through the gravitational effects of the Moon and Sun. El Niño-associated Kelvin waves carried pulses of warm water eastward toward the Americas, temporarily elevating coastal sea levels as they moved along the US West Coast. A marine heatwave added thermal expansion: warmer water occupies more space. NOAA described these factors as contributing together to the high water. Its coastal-water monitoring tools include live water-level observations and monthly high-tide flooding outlooks. Weather can worsen flooding and also bring flooding outside the dates highlighted by astronomical tide predictions.[1]
