Gaia and Porto share the same climate: mild Atlantic conditions with rain concentrated in winter and autumn, and warm, occasionally hot summers. The best time to visit is spring (April–June) or autumn (September–October), when temperatures are comfortable for walking and the port lodge tours are manageable without the summer crowds.
July and August are busy — both with Portuguese tourists and international visitors — and the waterfront restaurants and wine bars get crowded in the evenings. The port lodges are open year-round and operate tours daily regardless of season; booking in advance is advisable in summer for the most popular houses (Taylor's, Graham's).
Winter brings the October–March rains, which can be persistent and heavy. The view from Serra do Pilar in the fog has its own atmospheric quality, and the lodges are quieter. The Parque Biológico de Gaia is pleasant for a walk in any season.