September 2017: most active month on record in terms of Atlantic tropical cyclone ACE

The North Atlantic basin was extremely active in September 2017. Four tropical cyclones formed, all of which became hurricanes, and three of those four became major hurricanes, NWS National Hurricane Center in Miami, Florida said in their Monthly Tropical Weather Summary issued October 1, 2017.

Hurricane Irma was also present in the basin as a major hurricane during the month, although it formed in late August. Both Irma and Maria reached category 5 intensity during the month of September. 

Based on a 30-year climatology (1981-2010), the number of named storms forming in the basin during September was near average, but the numbers of hurricanes and major hurricanes were both well above average.

GOES-16 clean window view of Atlantic hurricanes August/September 2017. Loop shows storms Franklin through Maria using the 10.3-micron imagery from Goes-16. Credit: CIMMS Satellite Blog

In terms of the Accumulated Cyclone Energy (ACE), which measures the combined strength and duration of tropical storms and hurricanes, September 2017 was the most active month on record, easily breaking the previous record of September 2004. Overall, this September was about 3.5 times more active than an average September from 1981-2010.

From a seasonal perspective, activity in the Atlantic basin so far in 2017 is well above average, and this season is the 3^rd most active on record to date in the basin, behind 1933 and 2004. 

* Denotes a storm for which the post-storm analysis is complete.

Featured image: Hurricanes Katia, Irma and Jose – September 2017. Credit: NOAA/GOES-16