Ahead of and during the season, several national meteorological services and scientific agencies forecast how many named storms, hurricanes, and major hurricanes (Category 3 or higher on the Saffir-Simpson scale) will form during a season and/or how many tropical cyclones will affect a particular country. These agencies include the Tropical Storm Risk (TSR) Consortium of University College London, the National Oceanic and Atmospheric Administration (NOAA) and 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. Some of these forecasts also take into consideration what happened in previous seasons and an ongoing La Niña event that had recently formed in November 2017. On average, an Atlantic hurricane season between 1981 and 2010 contained twelve tropical storms, six hurricanes, and three major hurricanes, with an Accumulated Cyclone Energy (ACE) index of between 66 and 103 units.
The first forecast for the year was released by TSR on December 7, 2017, which predicted a slightly above-average season in 2018, with a total of 15 named storms, 7 hurricanes, and 3 major hurricanes. On April 5, 2018, CSU released its forecast, predicting a slightly above-average season with 14 named storms, 7 hurricanes, and 3 major hurricanes. TSR released its second forecast on the same day, predicting a slightly-below average hurricane season with 12 named storms, 6 hurricanes, and 2 major hurricanes, the reduction in both the number and size of storms compared to its first forecast being due to recent anomalous cooling in the far northern and tropical Atlantic. Several days later, on April 16, North Carolina State University released its predictions, forecasting an above-average season, with 14–18 named storms, 7–11 hurricanes, and 3–5 major hurricanes. On April 19, The Weather Company released its first forecasts, predicting 2018 to be a near-average season, with a total of 13 named storms, 7 hurricanes, and 2 major hurricanes. On May 24, NOAA released their first forecasts, calling for a near to above average season in 2018. On May 25, the UK Met Office released their prediction, predicting 11 tropical storms, 6 hurricanes, and an Accumulated Cyclone Energy (ACE) value of approximately 105 units. In contrast, on May 30, TSR released their updated prediction, significantly reducing their numbers to 9 named storms, 4 hurricanes and 1 major hurricane, citing a sea surface temperature setup analogous of those observed during the cool phase of the Atlantic multidecadal oscillation. On May 31, one day before the season officially began, CSU updated their forecast to include Subtropical Storm Alberto, also decreasing their numbers due to anomalous cooling in the tropical and far northern Atlantic.
From: Wikipedia https://en.wikipedia.org/wiki/2018_Atlantic_hurricane_season