Peak tourist season is roughly from mid-June to September, except in the Algarve where it really only quietens down in the dead of winter. Carnival and Easter are two holidays celebrated with gusto all over the country and are worth going out of your way for.
Portugal’s high season is mid-June to mid-September. The Atlantic tempers the Mediterranean climate down south, where summer temperatures regularly reach 30°C (86°F). The climate is temperate, and you’ll find agreeable weather just about everywhere (except in the Alto Douro and the Alentejo where summers can be painfully hot and droughts common) from April to October, and nearly year-round in the Algarve. Overall the wettest season is from November to March: the soggiest regions are in the extreme north and in the Serra da Estrela mountain region in the country’s centre. The ski season is from January to March, but February is best.