The period May to September is generally the best for a visit to Portugal Lisbon and the coasts around are sheltered. March and October are already suitable here for a holiday with pleasant temperatures. Northern Portugal can still be fresh and especially wet until May. The Algarve is a destination for all seasons. August is the holiday month for Portuguese and Spaniards, so a bit busier.
The north of Portugal has a mild maritime climate. In the summer it doesn’t get really hot, because the sun is often hidden behind the clouds. There is quite a lot of rain in the summer. The winter is very mild with a lot of rain. In the north-east of Portugal, snow sometimes falls in the mountains in winter. The south of Portugal is much warmer and drier than the north. The southern Algarve is one of the sunniest areas in Europe. The heat is bearable thanks to the usually blowing ocean wind. The hinterland of the Algarve, especially the provinces of Alto and Baixo Alantejo, is dry and hot.
Bring light clothing. You need a (fleece) sweater or cardigan for the cool evenings. Long sleeves and long pants provide protection against mosquitoes in the evening. Sturdy walking shoes also offer protection against snake bites. You need sturdy sandals on the coast. Water shoes with a sturdy sole protect against sharp stones and rocks. In religious buildings you must adhere to the dress code. Women wear their skirts or pants below the knee and the arms are completely covered. Men wear long trousers and the arms are covered to the elbow.