Rize is one of the wettest places in Turkey — the mountains trap moisture from the Black Sea and it rains throughout the year, including in summer. This is why the tea grows so well. Come prepared for rain at any time of year, even in August.
The best time for the city itself is May to September, when the tea plantations are in full growth and the mountains above are accessible. July and August are warm but rarely hot, with temperatures around 25°C on the coast. For mountain trekking in the Kaçkar, July and August are the prime months when the passes are snow-free.
Winter is damp and grey. The city functions normally but the upper mountain roads close. If you are primarily coming to trek in the Kaçkar, plan for June to September.