The Cold Waters in the Port of Genoa (NW Mediterranean Sea) during the Marine Heatwave in Summer 2022

Extreme weather phenomena have become more frequent and intense in recent decades in the context of climate change, and these include heat waves that affect both the atmosphere and seawater masses. In 2022, a summer marine heatwave (MHW) affected the entire Mediterranean Sea, and temperatures up to 5 °C above seasonal mean were reached in the Ligurian Sea in the NW part of the Mediterranean basin. In this scenario, the waters of the Port of Genoa (at the northern apex of the Ligurian Sea) distinguished themselves by maintaining lower temperatures than those of the open sea (a maximum gradient of −6.1 °C on 9 August 2022) after the passage of a fast-moving storm. In this study, the weather and sea parameters of the period (June–December 2022) are analysed to determine the phenomenon that caused the drop in temperatures in the water masses of the Port of Genoa. The sudden cooling of the water masses inside the port was caused by a heavy rainfall event in early August. Moreover, the isolation of the port water masses due to the weak dynamics of the period kept them stationary and locked inside the port. Seawater temperatures inside the port slowly rose again after the event, remaining cooler than outside temperatures throughout August (−0.3 °C on 31 August), reaching and exceeding outside temperatures on 3 September (26.4 °C), and remaining warmer until 3 November 2022 (21.5 °C).