Porto enjoys a cooler climate than Lisbon and the Algarve, although the temperatures tend to be mild. The summers can get really hot, but rarely intolerable. When the sun does beat down during an occasional heat wave, the city’s proximity to the Atlantic keeps the humidity down. There are plenty of glorious sun-filled days to enjoy in the summer.
Autumn is very agreeable, but when winter comes so does the rain. Porto experiences more rain than the southern part of the country, even outside of the wet season. Because of the higher amounts of precipitation, the countryside is rather lush and green. The Algarve doesn’t really have this kind of green, unless you count the golf courses.
Spring is a pleasant time to visit the city because the winter rains have abated. There’s plenty of sunshine, but without the soaring temperatures of summer.