Complex sentence: The season officially lasted from June 1,2000, to November 30,2000, dates which conventionally delimit the period of each year when tropical cyclones tend to develop in the Atlantic basin.
Split into simpler sentences: The season officially began on June 1,2000, and lasted until November 30,2000. The June through November dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin.