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Comparison between NOAA Coral Reef Watch’s newly-revised satellite-based Coral Bleaching Alert Area (bottom) with their previous, original Bleaching Alert Area product (top) for October 2023. The highest heat stress level in the original alert category system was Bleaching Alert Level 2, which equates to a HotSpot of 1 or greater and a Degree Heating Week of 8 or larger. The revised scale includes categories for Degree Heating Weeks of 8 through 20 or greater. NOAA Climate.gov image, based on data from Coral Reef Watch.