In July 2024, the National Oceanic and Atmospheric Administration (NOAA) released an assessment revealing that 35% of the global oceans were experiencing marine heatwaves (MHWs). This alarming percentage was the 14th highest ranking in almost 400 months of observation. NOAA, the authority on all things marine and atmospheric, also shared their forecasts for the rest of the year. They predict a decrease in MHW coverage to around 30% by October 2024. This reduction is expected due in part to the development of La Nina, a naturally occurring climate pattern that impacts global weather.
Marine heatwaves continue to have a significant impact on climate, with their intensity heightened in the northern hemisphere due to summer heat. This has led to the delayed recognition of a MHW off the North American West Coast, which is expected to weaken by the end of 2024. In contrast, strong MHWs continue off the East Coast of Asia, contributing to a possible longest duration of cool phase Pacific decadal oscillation (PDO).
The presence of MHWs in the Gulf of Mexico and the Caribbean Sea increases the risk of strong tropical cyclones in September and October. MHWs in the Mediterranean and Norwegian Seas also create potential for excessive precipitation from passing storms. These events demonstrate the wide-ranging impacts that MHWs can have on local and global climates.
Scientists at the Physical Sciences Laboratory are working tirelessly to better understand these phenomena. Their current efforts are focused on characterizing, understanding, and predicting MHWs. They are providing valuable resources such as current ocean maps, heatwave forecasts, and interactive tools.
Similarly, oceanographers at Mercator Ocean International are studying MHWs on a global scale. They provide 7-day forecasts and in August 2024, they forecast an increase in MHW intensity in the western Mediterranean basin and the Bay of Biscay. This is coupled with a predicted decrease in the mid North Atlantic and eastern Mediterranean basin.
MHWs are defined as extreme rises in ocean temperature lasting for at least five consecutive days. They are categorized based on their deviation from the mean temperature. It is anticipated that MHWs will continue to grow in the Bay of Bengal, within moderate and strong categories, despite a predicted decrease in intensity in the center of the Indian Ocean. This prediction underscores the urgent need for continued study and mitigation strategies for these ocean heatwaves.
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