Hurricane Season 2013: Least Active Since the 1990s

The 2013 Atlantic hurricane season was the least active season so far this century, and among the quietest on record since 1950.

Tracks of named tropical storms and hurricanes in the 2013 Atlantic hurricane season.

• ENLARGE MAP

Graph of Atlantic Basin ACE index by year from 1970-2013. The 2013 total is highlighted in red at the far right. (Credit: Weather Underground)

• ENLARGE GRAPH

While the total of 13 named storms was one more than the 30-year average of 12 named storms, that doesn't tell the whole story.
A better method of summing up hurricane season activity than simply counting storms utilizes the Accumulated Cyclone Energy, or ACE, index. This is calculated by adding each tropical storm or hurricane's wind speed through its life cycle. Long-lived, intense hurricanes have a high ACE index. Short-lived, weak tropical storms, a low ACE index. Summing up the ACE indices of each storm or hurricane will give you an ACE index for the entire season.
The bar graph at right from Weather Underground shows just that. Notice the paltry ACE index of 33 in 2013.
Since 1950, there were only five other hurricane seasons less active than 2013:

• 1983: 17
• 1977: 25
• 1972: 28
• 1982: 29
• 1994: 32

That stretch from 1982-83 was one of the strongest El Niño events on record. Increased wind shear during stronger El Niño events tends to suppress tropical cyclone development. Indeed, only 10 named storms formed during the 1982 and 1983 seasons, combined, though one was destructive Hurricane Alicia. In 2013, the equatorial Pacific was in a neutral state, neither El Niño, or its opposite, La Niña, was in play.
An average season's ACE index is about 110. Hurricane Ike in 2008 had an ACE index of 39, more than the entire seasons of 2013, 1983 and 1982.
(MORE:  Weather Underground ACE Page)
Only two Atlantic Basin storms strengthened to hurricanes in 2013, Humberto and Ingrid. Humberto pushed the record for the latest first Atlantic hurricane of the season, waiting until Sept. 11. Ingrid became a hurricane in the far western Gulf of Mexico before sliding into eastern Mexico.
Furthermore, there was not a single major hurricane, Category 3 or stronger on the Saffir-Simpson hurricane wind scale, this season. According to Digital Meteorologist Chris Dolce (Twitter), the last season lacking a single major Atlantic hurricane was 1994.
(MORE:  Hurricane Season By The Numbers)
Eight of the season's 13 named storms eventually succumbed to either dry air, strong wind shear or both. This includes each storm forming in the central and eastern Atlantic Ocean, as well as Tropical Storm Karen.