 In advance of , and during , each hurricane season , several forecasts of hurricane activity are issued by national meteorological services , scientific agencies , and noted hurricane experts . These include forecasters from the United States National Oceanic and Atmospheric Administration ( NOAA ) ' s National Hurricane and Climate Prediction Center , Tropical Storm Risk , the United Kingdom 's Met Office , and Philip J. Klotzbach , William M. Gray and their associates at Colorado State University ( CSU ) . The forecasts include weekly and monthly changes in significant factors that help determine the number of tropical storms , hurricanes , and major hurricanes within a particular year . According to NOAA and CSU , the average Atlantic hurricane season between 1981 and 2010 contained roughly 12 tropical storms , six hurricanes , three major hurricanes , and an accumulated cyclone energy ( ACE ) index of 66 – 103 units . NOAA typically categorizes a season as either above @-@ average , average , or below @-@ average based on the cumulative ACE Index , but the number of tropical storms , hurricanes , and major hurricanes within a hurricane season are considered occasionally as well . 
