The WORLD GUIDE says:

"East Asia’s wind and weather is broadly determined by the Asian monsoon climate. Low pressure over the continent dominates in summer as intense sunshine creates rising air above the landmass. A humid air-mass is drawn between this heat low and the sub-tropical Pacific High, introducing a weak southerly airflow into the region. In rainy season, the South China Sea’s tropical zones receive ten times more rain than the rest of the year. This is the hottest time of year with temperatures over 30°C. The water also warms up to 28-30°C, enabling... " world guide