May and June are widely regarded as the best months for a coastal visit. The weather is warm and sunny, the sea is swimmable from mid-May onwards, the tourist sites are open, and prices are significantly lower than in peak summer. The Montenegrin coast in late May has a particular charm — flowers everywhere, uncrowded beaches, and restaurant owners who are happy to see you.
July and August are peak season on the coast. Kotor Bay and Budva fill up with Serbians, Russians, and Western Europeans; accommodation prices double or more; queues form at everything; and the old towns get genuinely jammed on days when cruise ships dock. The coast is still beautiful but it's a significantly less relaxing experience. Book accommodation well in advance.
September and October offer a good compromise. Prices fall, crowds thin, the sea stays warm through September, and the light in early autumn is exceptional. Some smaller restaurants and seasonal operations start to close down in October.
November to April is quiet on the coast — many things close and the weather is wetter. However, Durmitor and Bjelasica have ski seasons running roughly December to March. Kolašin, the main base for Bjelasica skiing, is a small ski town with a genuine local feel. Žabljak for Durmitor is more basic but the scenery is outstanding. Snow on the mountain plateaux can persist into May.
Montenegro has two distinct climates: Mediterranean on the coast (hot, dry summers; mild, wet winters) and continental/sub-alpine in the north (warm summers; cold, snowy winters). Podgorica, in the central valley, has ferociously hot summers — often the hottest city in Europe in July.