The best weather in Barcelona is on June. The average day temperature is around 24°C and the lowest day temperature is 15°C. With 15 hours of daylight and 12 hours of sunshine, a sunny weather is guaranteed. Rain can fall for up to 24mm over ten days during the month but the clouds clear fast and the sun shines again. The seawater temperature is approximately 21°C.
Barcelona in June is hosting two very important events, the Catalan Motorcycle Grand Prix (Moto GP) and the European Balloon Festival (4 days competition). It is recommended to attend either one.
The advantage of traveling to Barcelona in June is mainly the warm but not very hot weather, which is perfect for a summer holiday. Officially, the warm season starts on June 22. Moreover, many festivals and events are taking place so expect during certain days and weekends the town and the resorts to be crowded.