Sea Temperatures in the Algarve Exceed the 20-Year Average

Between June 28 and July 9, 2025, the Faro Coastal buoy — part of the national ocean monitoring network operated by the Portuguese Hydrographic Institute (MONIZEE) — recorded sea surface temperatures significantly above the 20-year average. These values indicate the occurrence of an extreme phenomenon known as a marine heatwave.

A marine heatwave is defined as a period in which the daily sea temperature exceeds a high statistical threshold — the 90th percentile of the average temperature for that region and time of year — for at least five consecutive days.

This means that the temperatures observed in Faro during this period ranked among the top 10% of all values recorded over the past two decades. In this case, the daily sea surface temperature exceeded the average temperature by more than 5°C, classifying it as an extreme marine heatwave.

The average temperature benchmark was determined from records collected in Faro between 2004 and 2024 and serves as the reference to identify marine heatwave events.

You can monitor sea surface temperature conditions at https://geomar.hydrographic. en .

Figure Caption:

Fig01 – Coastal Lighthouse Buoy.

Fig02 - Real-time Sea Surface Temperature Records from the Faro Coastal Buoy (CSA82-D).

Fig03 - Analysis carried out for the detection of the marine heatwave using the reference average temperature (2004–2024), the corresponding 90th percentile, and daily temperature data from the Faro buoy in 2025.