The Atlantic Hurricane Season in the Northern Hemisphere begins around the end of May and lasts through the end of November. During this period, ocean temperatures are warm enough to allow for enough evaporation to provide the thermodynamic energy needed for tropical weather systems to grow.
This past summer, there was a notable absence of tropical storms in the Atlantic due mostly to a large plume of Saharan dust which cooled the atmosphere and inhibited storm development.
That dust is now gone and the waters of the tropical and near-tropical Atlantic have warmed up greatly due to the absence of storms during summer, setting the stage for an active fall. September and October are the peak months for Atlantic hurricanes because ocean temperatures are warmest this time of year. And the ocean is exceptionally warm this year.