Although hurricanes can form as early as late May and continue into December in the Caribbean Sea or the Gulf of Mexico, the official Atlantic hurricane season starts June 1st and ends November 30th. In the eastern North Pacific, the official season begins May 15th and ends November 30th. Both official seasons cover more than 99% of all tropical cyclones in any year.
During this time, the National Hurricane Center (NHC) maintains a continuous watch on tropical cyclones over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico, as well as the eastern North Pacific. They also issue public watches and warnings.
In the Atlantic Basin (the North Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea), hurricane season is typically most active between mid-August through October. Height of the season is in mid-September.
For hurricane development location, check the origins of tropical cyclones.