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The 2017 hurricane season was an extremely active one. The season was characterized by well above-average numbers of named storms, hurricanes, major hurricanes as well as duration and integration metrics such as hurricane days and Accumulated Cyclone Energy (ACE). Our initial seasonal forecast issued in April underestimated activity in 2017 by a large margin, due in part to El Niņo predictions by many statistical and dynamical models that did not come to fruition. Later seasonal forecasts issued in July and August correctly predicted an above-average season but still considerably underestimated just how active the season was going to be.

Six consecutive two-week forecasts were issued during the peak months of the Atlantic hurricane season from August-October. These forecasts were based on current hurricane activity, predicted activity by global forecast models and the phase of the Madden-Julian Oscillation (MJO). These two-week forecasts generally verified well.

 Integrated measures such as Net Tropical Cyclone (NTC) activity and Accumulated Cyclone Energy (ACE) were at top ten levels based on Atlantic hurricane data going back to the mid-19th century. Well above-average sea surface temperatures and reduced levels of vertical wind shear in the tropical Atlantic were two of the primary reasons why such an active season was observed.

While the season was very active, it will be most remembered for several hurricanes that devastated portions of the continental United States as well as islands in the Caribbean and other parts of the tropical Atlantic. Hurricane Harvey brought epic flooding to the Houston metropolitan area, while Irma and Maria both brought devastation to islands throughout the Caribbean and tropical Atlantic. Irma also made landfall in the Florida Keys as a Category 4, pummeling the Keys and bringing considerable damage to mainland Florida as well. The 2017 Atlantic hurricane season was also the first season on record (since 1851) to have two Category 4 hurricanes make continental United States landfall in the same year (Harvey and Irma).

(Credit: Colorado State University)