Weather will likely play an important role when you plan your trip to Hai'an, but bear 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 temperature of 25°C, while the coldest months are January and February, with an average of 6°C. The rainiest months in Hai'an are July, June, August and September, with each month seeing an average of 200 mm of rainfall.