Barcelona Supercomputing Center, 2016 - Legal Notice

Post Mortem 2020

The extremely active 2020 Atlantic basin hurricane season came to an end on 30 November. The season broke the record for most named storms in a single Atlantic season on record. Year 2020 had 30 named storms, eclipsing the old record of 28 named storms set in 2005. The season also produced the 2nd most hurricanes on record with 13 (trailing only 2005 with 15 hurricanes) and tied for the 2nd most major (Category 3+) hurricanes on record with 6 (trailing only 2005 with 7 major hurricanes). Accumulated Cyclone Energy (ACE), an integrated index accounting for frequency, intensity and duration of storms was also well above-average. The 2020 Atlantic hurricane season produced 180 ACE – the 6th-most ACE for an Atlantic hurricane season in the satellite era (since 1966). Final ACE values may change slightly in post-season reanalysis of tropical cyclone intensity by the National Hurricane Center. The 1981-2010 average values of these quantities are 12 named storms, 6 hurricanes, 3 major hurricanes and an ACE of 106.

In general, Atlantic seasonal hurricane forecasts called for an active season at all lead times (from March/April through July/August). The average of all seasonal forecasts for March/April to May/June changed little, while most seasonal forecasts increased from May/June to July/August, given anomalous warming of the tropical Atlantic and a stronger trend towards La Niña conditions. The average of all seasonal outlooks issued in July/August was extremely close to the observed value for ACE (181 forecast vs. 180 observed). Overall, the peak of the Atlantic hurricane season (August-October) was characterized by above-normal sea surface temperatures and below-normal shear across most of the tropical Atlantic and Caribbean.

The average values predicted by all groups issuing forecasts in March/April were 17 named storms, 8 hurricanes, 4 major hurricanes and an ACE of 148. These numbers changed little in May/June (17 named storms, 8 hurricanes, 4 major hurricanes and an ACE of 152). The average prediction issued in July/August increased from May/June and called for 22 named storms, 10 hurricanes, 5 major hurricanes and an ACE of 181. It should be noted that not all forecast groups issue predictions for all four tropical cyclone intensity metrics. In terms of Accumulated Cyclone Energy, the most accurate March/April seasonal forecast came from Weatherbell (170 predicted vs. 180 observed), while the most accurate May/June and July/August seasonal forecast came from WeatherTiger, which predicted exactly the observed ACE of 180.

In addition to setting the basinwide named storm record, the season was also extremely active from a landfalling perspective, with 12 named storms making landfall in the continental United States (the most on record) and 6 of these at hurricane strength (tied for the most on record). The strongest of these landfalling continental United States hurricanes was Laura, a Category 4 hurricane that devastated southwest Louisiana, causing ~$16 billion dollars in damage and 42 fatalities in the United States. Two Category 4 hurricanes also slammed into Nicaragua just 13 days apart in November – Eta and Iota. Over 250 fatalities and $8 billion dollars in damage have been attributed to these two hurricanes.

A more in-depth discussion of the 2020 Atlantic hurricane season is available from Colorado State University.

Listen to the discussion on the 2020 hurricane season recording - with the participation of L.P. Caron (BSC), P. Klotzbach (CSU) and R. Truchelut (WeatherTiger).