The climate is humid subtropical, very pleasant, with the highest air temperature averaging 25 °C (77 °F) during August and lowest averaging 6 °C (43 °F), in January. Summers are usually warm during the day and cooler near the evening, although heat wave patterns are also common. 

Annual weather averages for Opatija are available here.

Current weather forecast for Opatija: 

OPATIJA WEATHER

Detailed weather forecast is available at Meteo.hr website. 

MIC 2019