Why go
Porto's slopes, river mouth and nearby beaches make weather part of the plan. Summer is usually sunny but can turn cool or showery; winter is mild rather than reliably dry. The coast is often windier and cooler than the city, so a river walk and beach visit need different layers.
The full story
Porto sits where the Douro reaches the Atlantic, so its climate has a Mediterranean pattern tempered by the coast. Summers are generally warm and dry, although cooler rainy spells can interrupt them. Heatwaves occur, but the nearby coast is often noticeably windier and cooler than the built-up city. Winters are mild, with rain that can persist over long stretches before clearer periods return. That contrast is useful when choosing a day: use a clear summer morning for exposed viewpoints and riverside walks, but take a layer for the coast and a waterproof in the wetter months. The steep older streets also feel more demanding on wet stone, particularly when walking between the upper city and the river in the centre.