Marine heatwaves push sea temperatures off Portugal’s Algarve coast above 26°C

Sea surface temperatures off Portugal’s Algarve coast have reached 26.1°C, with the Portuguese Navy reporting two marine heatwaves off Faro over the past three weeks, including one classified as “strong”.

The Portuguese Navy said on Thursday that the two events were recorded between June 15 and July 9 by the Faro Coastal buoy, part of the Portuguese Hydrographic Institute’s MONIZEE coastal monitoring network.

During the period, the buoy measured an average daily sea surface temperature of around 25°C.

Marine heatwaves are defined as periods of at least five consecutive days during which sea surface temperatures remain significantly above the seasonal average for a particular location.

Scientists warn that such events can disrupt marine ecosystems, affect fisheries and aquaculture, and have become more frequent and more intense as global temperatures rise.

According to the Navy, the first event was classified as a moderate marine heatwave, reaching a maximum daily sea surface temperature of 23.3°C, around 1.5°C above the threshold corresponding to the 90th percentile for that time of year.

The second episode was classified as strong, with a maximum daily average temperature of 24.8°C, approximately 2.2°C above the same threshold.

Although marine heatwaves are classified according to how long elevated temperatures persist, rather than the highest temperature recorded, the Navy highlighted that the buoy measured an instantaneous peak of 26.1°C, illustrating the extent of warming observed off the Algarve coast.

The MONIZEE monitoring network provides near real-time observations of sea surface temperatures around Portugal’s coastline, helping scientists track extreme ocean events and changes in coastal waters.

The Portuguese Navy said the information collected is important for environmental monitoring, improving understanding of ocean temperature variability, and supporting activities that depend on marine conditions, including fisheries, navigation and coastal management.

Natasha Donn

Journalist for the Portugal Resident.