Porto and its metropolitan area feature a Mediterranean climate (Köppen: Csb) with mild wet winters and warm dry summers. According to the Troll-Paffen climate classification, Porto has a warm-temperate subtropical climate (Warmgemäßigt-subtropisches Zonenklima),[1] and a subtropical climate according to Siegmund/Frankenberg.[2] Porto is the wettest major city with a Mediterranean climate.
Porto has generally moderate temperatures. The average annual high is around and average low around . The climate is also only mildly seasonal, from a maxima of in January to 25- in August, while minima is around 5- in January and 15- in July and August. In its metropolitan area, January lows can vary between at the coast and on the mountainous interior, and August highs vary between at the coast and in the interior near the Douro valley.[3]
Due to its coastal position, temperatures below freezing are rare, and frosts are never severe. Porto is placed in the USDA hardiness zone 10a.[4] The lowest temperature ever recorded in the city was on 11 January 1941.[5]
Porto has abundant levels of precipitation. Despite averaging above 1000mm of precipitation a year, July and August are relatively dry with around 15mm30mm falling each month. The wettest period is between October and February, mostly between October and December, the wettest month.
The average relative humidity is around 77%. 81% from November to January and 73% in the summer. Summer can be slightly muggy in the hottest days but is generally comfortable, as temperatures rarely surpass .[6]
Despite its precipitation, the total hours of sunshine are relatively normal for a region of its latitude. Winters, especially December, are somewhat dull, and summers are sunny.
As a coastal Atlantic city, winds are most predominant in winter. In the summer, nortada winds prevail and can refresh the city in the hottest days. The city centre is sheltered and seldom gets any strong winds.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Porto (Fontainhas) | 19.6 | 19.7 | 19.2 | 19.0 | 18.1 | 16.9 | 17.3 | 16.3 | 15.2 | 16.8 | 18.4 | 20.0 | 18.0 |
| Porto São Gens | 8.6 | 8.7 | 8.8 | 9.0 | 8.3 | 7.7 | 7.4 | 6.8 | 6.5 | 6.5 | 6.5 | 6.9 | 8.4 |
| Porto Pedras Rubras | 15.7 | 16.3 | 15.0 | 15.0 | 14.9 | 13.5 | 12.5 | 12.2 | 11.9 | 13.3 | 14.2 | 16.3 | 14.2 |
