File:Severe Storms Approaching the West Coast of the United States (MODIS 2024-01-01).jpg

English: Strong storms brewing over the Pacific Ocean brought spectacular—but dangerous—surf to the West Coast of the United States in the closing days of 2023. The intense storms created giant waves, many measuring more than 20 feet (6 meters) when they slammed into the California coast. According to media reports, at least eight people were injured by waves when watching the incoming surf near Ventura. In some locations along the coast, strong surf made deposited copious debris across roadways, making them impassible. The storms also brought rain to lower elevations and snow in the high country. On December 28, Caltrans announced the closure of part of Highway 89, which lies in the high Sierra Nevada mountains near Lake Tahoe in anticipation of incoming severe snowfall.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired a true-color image of storms across the eastern Pacific Ocean on December 28, 2023. Although the storm centers were located over open ocean, the leading edge had reached California. Giant waves were crashing against the shore while skies remained fair with little or no rain on that day.

Measuring atmospheric pressure is one method of measuring intensity of a storm. The lower the pressure, usually measured in millibars, the more intense the storm’s strength. Standard pressure in millibars is 1,013.25, while typical storm systems start at 1,000 millibars. According to NOAA surface intensity charts, one offshore storm reached peak minimum pressure of 960 millibars and the second measured as low as 970 millibars at its peak strength.

NOAA publishes a Dvorak Current Intensity Chart, which correlates several features of storms including wind speed and atmospheric pressure in millibars. According to this chart, a Pacific storm with mean sea level atmospheric pressure (MSLP) of 954 mb is estimated to have a wind speed of 90 mph, while a storm with MSLP of 976 mb has an estimated wind speed of 75 mph. Those wind speeds are equivalent to a Category 2 or Category 1 hurricane on the Saffir-Simpson Hurricane Wind Scale, respectively. Both storms fell within these parameters.