Rostock has a Baltic maritime climate — cool summers, mild winters, and a good deal of wind off the sea. The warmest months are July and August, when Warnemünde beach fills with German holidaymakers. This is also when most cultural events take place, including the Warnemünde Week sailing regatta in late July, one of the largest sailing events in northern Europe.
Spring and early autumn are the best times for visiting the old town without crowds. May and June are often pleasant — warm enough for outdoor cafes, without the summer press. October can be beautiful with autumn colour in the parks and a quieter, more local feel.
Winter is cold and grey but not extreme, and the city has a genuine Advent market in December. The Baltic can be wild and atmospheric in winter, making Warnemünde worth a visit even when swimming is out of the question.