Water temperatures along parts of the northern coast have climbed above those in the Algarve, reversing what is normally expected during the summer.

The reason isn't a heatwave in the north, but rather the absence of one of Portugal's best-known summer weather features: the nortada, the strong northerly wind that usually blows along the west coast.

Usually, the nortada blows the warmer water away from the coast, and colder water comes up from deeper in the ocean to replace it. This is why the sea along Portugal’s west coast can feel surprisingly cold, even when the weather is very hot.

This week, however, the northerly winds have been much weaker than usual. Without them, the warm surface water has remained close to the coast, allowing sea temperatures in northern Portugal to rise above those in the Algarve. As stated by the Portuguese Institute for the Sea and Atmosphere (IPMA), water temperatures have reached around 20°C in the north, while the Algarve has been sitting at around 19°C.

The difference is only expected to be temporary. Meteorologists say the nortada could return over the coming days, bringing back the usual upwelling and cooler water along the western coastline.

Why can the Algarve still feel colder?

The Algarve may be the warmest part of Portugal, but that does not always mean the sea is warmer everywhere. Around Sagres and the Costa Vicentina, the strong Atlantic influence often keeps the water noticeably cooler. Further east, in places such as Tavira, Monte Gordo and Vila Real de Santo António, the sea is usually warmer and often more inviting for swimming.

So while many visitors expect the Algarve to always have the warmest water, nature occasionally has other plans. This week's unusual conditions are a reminder that the Atlantic is constantly changing, and even long-standing summer patterns can take a short break.