Most of Portugal has a hot-summer Mediterranean climate according to the Köppen climate classification: "Csa" in most of the lands south of the Tagus River, inland Douro Valley in the Norte Region, eastern Azores and the Madeira archipelago. The "Csb" warm-summer Mediterranean pattern can be found north of that same river and in Costa Vicentina in coastal Southern Portugal. Most of the Azores have a humid subtropical climate or "Cfa", while a small region in inland Alentejo has Bsk or semi-arid climate. The Savage Islands are the only region to have an arid climate. The sea surface temperatures in these islands vary from in winter to in the summer, occasionally reaching .
