Mykolaiv has a continental climate moderated by its proximity to the Black Sea. Summers are hot and dry — July and August regularly reach 30°C or above — with low humidity and long daylight hours. Winters are cold but not extreme: January averages around -3°C, with occasional snow. The city sits in a steppe zone, meaning rain is unevenly distributed and the landscape goes dry and brown in late summer.
Spring (April–May) is probably the best time to visit in normal circumstances. Temperatures are comfortable in the 15–22°C range, the parks and boulevards are in leaf, and the outdoor cafe culture picks up. Early autumn (September–October) is similarly pleasant, with warm days and reduced summer heat.
Summer is functional but hot. The outdoor life suits the heat if you start early and slow down at midday, and the rivers offer some relief. Winter is quiet and cold; the city's cultural institutions stay open, which matters if the archaeological site and museums are your primary interest.
Note on the current situation: Since the Russian invasion in 2022, Mykolaiv has experienced significant damage from shelling and its infrastructure and services have been disrupted. The security situation is the overriding consideration for any visit — consult current advisories from your government and the Ukrainian authorities before making any travel decision. The timing of a visit in the traditional travel sense is secondary to whether travel is safe or possible at all.