Weather is probably a major factor when you plan your trip to Hai'an, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually July and August with an average temp of 77°F, while the coldest months are January and February with an average of 43°F. The rainiest months in Hai'an are July, June, August, and September, with each month seeing an average of 8 inches of rainfall.