Tropical cyclone forecasting uses statistical methods based on tropical cyclone climatology, as well as methods of numerical weather prediction where computers use mathematical equations of motion to determine their movement. The World Meteorological Organization continues to create and maintain the annual hurricane naming lists. Naming lists use a six-year rotation, with the deadliest or most infamous storm names retired from the rotation. The current acting director of the National Hurricane Center is Edward Rappaport following the retirement of Richard Knabb on May 15, 2017. Rappaport was succeeded by Kenneth Graham on April 1, 2018.