Portugal is a tiny country, roughly the size of the US state of Indiana, yet it holds astonishingly diverse microclimates. The assumption that the entire country is dependably hot and sunny year-round is a fundamental error.
The North (Porto, Minho, Douro)
The Celtic north is heavily influenced by the Atlantic. Winters here are undeniably wet, cool, and grey (averaging 5-14°C / 41-57°F). This rain is exactly why the Minho region is so spectacularly verdant.
In the summer, the coastal regions (like Viana do Castelo and Moledo) remain very temperate, rarely breaking 28°C (82°F) due to the nortada—the intense, reliable northerly wind. This wind makes the region beloved by wind-sport enthusiasts; if you visit between June and September to cool off, you will see kitesurfers dominating the massive waves. However, drive just 100 kilometers inland to the Douro Valley, and the wind vanishes. The Douro acts as an oven in August, with temperatures frequently surpassing 40°C (104°F).
The Center (Lisbon & Silver Coast)
Lisbon experiences a Mediterranean climate strongly mediated by the Tagus river. Winters are mild (8-15°C / 46-59°F) and moderately rainy. Summers are gloriously sunny and hot (25-30°C+ / 77-86°F+), but invariably cooled by a late afternoon breeze.
However, the nearby town of Sintra possesses its own unique microclimate. Because of its densely forested mountains, Sintra is almost always 5°C cooler than Lisbon and frequently shrouded in a thick, romantic mist. Always carry a sweater when leaving Lisbon for Sintra.
The South (Alentejo & Algarve)
The interior plains of the Alentejo are arguably the hottest place in the country during summer. Temperatures routinely exceed 40°C (104°F) in July and August. The land bakes, the cork oaks shimmer in the heat haze, and nobody moves between 1 PM and 5 PM.
The Algarve coast, screened from northern winds by small mountain ranges, is genuinely sunny almost 300 days a year. Even in January, you can often wear a t-shirt in the midday sun (16°C / 61°F). In summer, it hovers around 30°C (86°F), tempered by calm ocean breezes.
The Islands (Madeira & Azores)
Madeira: The island of eternal spring. Closer to Africa than Portugal, it hovers between 17°C and 25°C all year round. The north of the island is wetter and greener, the south is drier and sunnier.
The Azores: A mid-Atlantic, subtropical volcanic archipelago. The weather here changes four times a day. Expect spectacular sun, heavy rain showers, thick fog, and brilliant rainbows all within a 24-hour cycle. Pack highly adaptable, waterproof layers.