September is a very important month for Nicaragua. Independence day is celebrated on the 15th of September and the day before is the anniversary of the Battle of San Jacinto.
These two days along with many other are celebrated throughout the whole country as national holidays. Typically people will take the day off work and spend time with their loved ones watching parades, enjoying meals and celebrating with friends and family. This is a great time of year to be a tourist in Nicaragua as you get the full cultural immersion that can only come from an authentic experience.