Bayonne has a mild Atlantic climate — warm summers, mild winters, and rain year-round. The driest months are June through September. July and August are busy with summer tourists but the town still functions normally, unlike some coastal resorts.
The Fêtes de Bayonne in late July or early August is one of the great street festivals of Europe — five days of music, dancing, and bullfighting attended by over a million people. The streets fill with people in white with red scarves, and the festivities run from midday to dawn. Book accommodation months in advance if you plan to attend; it is worth it if you are willing to embrace the chaos. If you prefer a quieter visit, May and June offer good weather and empty streets.