“These figures indicate the occurrence of an extreme phenomenon called a 'marine heatwave'," reads a statement from the AMN.

According to this institution, between 28 June and 9 July 2025, the Faro Costeira buoy, which is part of the Hydrographic Institute’s national ocean monitoring network (MONIZEE), recorded maximum water temperatures of 25.1º Celsius.

A “marine heatwave” is considered to have occurred if the daily sea temperature exceeds, for at least five consecutive days, a high statistical limit, called the 90th percentile of the average temperature for that region and time of year.

According to the authority responsible for navigation safety and control and for the preservation and protection of natural resources, this means that the temperatures observed in Faro during the period in question are “among the 10% highest of all those recorded in the last two decades”.

“In this case, the daily sea water temperature recorded in Faro exceeded the 90th percentile by more than 5°C, corresponding to the category of marine heatwave considered extreme,” concludes the AMN.

The average temperature was determined from records collected in Faro over the last 20 years (2004–2024), serving as a reference for identifying marine heatwave events.