The official Atlantic hurricane season currently runs from June 1st to November 30th.
However, the main ingredient for a hurricane is warm surface waters in the ocean. As a result, hurricane season depends more on the temperature than on the time of year. The latest tropical cyclone to attain tropical storm intensity was Tropical Storm Zeta on December 30, 2005. It was one of only two storms in history to exist in two calendar years (the other being Hurricane Alice in 1954, which was the latest forming tropical cyclone to attain hurricane intensity).