Y - Never used as a letter for start of a Tropical Storm/Hurricane name.... so there can never be a Hurricane Yogi or Yolande , for example. There are rarely more than 21 Tropical Storms/ Hurricanes that occur in any year , so Q, U, X and Z are also never used .
If it is an unusual year that exceeds 21 cases, the Greek letters alpha, beta, gamma , etc, are employed.
Strange how that naming system has evolved, although it may change in time.