Complex sentence: These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin, although in actuality the season continued to the end of 1954 and into 1955 due to the second Hurricane Alice--the first such overlap ever recorded.
Split into simpler sentences: These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The season continued past its official bounds into 1955 due to the second Hurricane Alice--the first such overlap ever recorded.