El Nino’s impact on the hurricane season

 

Hurricane Joaquin, October 2015 (Source: NOAA)

NOAA recently issued a statement saying a very strong El Nino event is likely during the upcoming fall and winter in the Northern Hemisphere. That could have profound effects on the Atlantic hurricane season and is reflected in NOAA’s forecast for a below average season.

Since 1950, there have been three separate “very strong” episodes of El Nino that led to a seasonal average of seven tropical storms, three hurricanes and only one major hurricane. That’s compared to the normal seasonal average of 14 tropical storms, 7 hurricanes and 3 major hurricanes. The current hurricane season could mirror one of these three prior seasons that also had a “very strong” episode of El Nino.

2015-2016 (2015): The 2015 Atlantic hurricane season was below average with only 11 tropical storms, 4 hurricanes, including 2 major hurricanes. The strongest storm this season was Hurricane Joaquin in late September and early October. It reached peak intensity on October 1 as a borderline Category 4/Category 5 storm with peak sustained winds of 155 mph. However, the only storms to make landfall in the United States that season were Tropical Storms Ana and Bill.

This season’s ACE score was only 62.7 and while relatively high for an El Nino season, still much lower than the seasonal average ACE score of 123 10⁴ knot² (1991-2020). The ACE score is a more accurate measure of how busy a season is than just the overall number of named storms. It takes into account the number of tropical storms and hurricanes, as well as the intensity and duration of the storms.

1997-1998 (1997): This season had a particularly strong El Nino. There were only 8 tropical storms, 3 hurricanes and 1 major hurricane. The strongest hurricane of the season was Hurricane Erica that peaked at Category 3 intensity (125 mph sustained winds) over the open Atlantic. Erica was the only named storm in the Atlantic in August or September. 1997’s final ACE score – a measure of tropical storm and hurricane intensity and duration – was 41.

1982-1983 (1983): Since the majority of the 1970s and 1980s saw below average Atlantic hurricane seasons, the 1983 season didn’t stand out as much at the time. It occurred during another very strong episode of El Nino and had only 4 tropical storms with 3 hurricanes and 1 major hurricane. The major hurricane was “Alicia.” A Category 3 storm, Alicia developed off the Texas Gulf Coast where it made landfall. Major impacts occurred in Houston and it was the costliest hurricane in U.S. history at the time. The 1983 season, as a whole, however, was exceptionally quiet and had an ACE score of only 17.4. That remains the lowest ACE score for any Atlantic hurricane season since the satellite era began in the 1960s.