Although my colleague Peter Holland declared the Atlantic hurricane season officially closed, there are reports in the media that environmental conditions in the North Atlantic basin may be favorable enough to sustain tropical cyclones, potentially adding to what has already been a very active year and perhaps foretelling an early start to hurricane activity in 2018.
The official hurricane season for the North Atlantic runs from June 1 to November 30 and encompasses over 97 percent of annual climatological activity. Out-of-season tropical systems — events happening through December to May — are rare, but not unprecedented. The U.S. National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD) states that since 1851, 88 storms have been observed in the Atlantic during the off-season — that’s about one out-of-season storm every two years. In theory, this could be an underestimate, as the peer-reviewed literature suggests an undercount of Atlantic tropical cyclones prior to the satellite reconnaissance era.