Why is it so cold in summer in Qingdao?

Summer in Qingdao comes late and leaves late, because it is close to the sea. It's getting hot at the end of June now. Although the temperature in Qingdao is relatively low, such as about 35 degrees inland, it is only about 25 degrees in Qingdao at this time, but the humidity is very high, so it is very stuffy. The seaside will certainly be better, but if it is 25 degrees inland, it will be very cool. If the temperature reaches about 35 degrees in July and August, it is impossible to pass NND. This is the case.