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.

Weather Quiz

 

August in Washington, D.C.

During what month has triple-digit heat been most prevalent in the nation’s capital this century? 

A.  June

B.  July

C.  August

D.  September

2026 Atlantic hurricane update

 

An afternoon along Dewey Beach, Delaware

The peak of the Atlantic hurricane season is quickly approaching in September. That's when atmospheric and environmental conditions are the most favorable for tropical storm and hurricane development. Earlier this month, NOAA updated its seasonal hurricane forecast to reflect the tropical activity over the first two months of the season.

NOAA's updated forecast calls for a seasonal total of 7-13 tropical storms, of which 2-6 could become hurricanes, with 0-2 major hurricanes. That includes the three tropical storms that have already occurred this season. An "average" hurricane season features 14 tropical storms, 7 hurricanes and 4 major hurricanes. The primary reason NOAA has maintained its expectation for a below average Atlantic hurricane season is an intensifying – and potentially historic – episode of El Nino.

One of the trademarks of El Nino conditions in the tropical Atlantic is an increased amount of wind shear. Wind shear refers to winds that change in both speed and direction at different levels of the atmosphere. Above average wind shear means conditions are less favorable for tropical development. Tropical systems require calm winds – or the absence of wind shear - to develop. They also require warm ocean water, typically at least 80° Fahrenheit, which serves as its fuel source. Another hallmark of an El Nino event is cooler than average sea surface temperatures across the Main Development Region or “MDR” of the tropical Atlantic.

The three tropical storms that have already developed this season were relatively weak and short-lived. Only Bertha impacted the United States, having developed near the Gulf Coast last month. No hurricanes have developed anywhere in the Atlantic Ocean since last October. That makes this the first season since 2022 that no Atlantic hurricanes have developed through mid-August.

The National Hurricane Center doesn't expect any tropical storms to develop anywhere in the Atlantic over the next week. However, despite the El Nino conditions, recent seasons have shown that things in the tropical Atlantic can ramp up in a hurry. The 2017 Atlantic hurricane season, for example, got markedly more active in late-August, starting with Hurricane Harvey. September 2017 saw four major Atlantic hurricanes, including two Category 5 powerhouses (Irma and Maria). 

However, the key difference between 2017 and this season is that a weak episode of La Nina developed in 2017 and that helped create more favorable conditions for an active hurricane season. That’s unlike the potentially historic El Nino this summer and fall. Still, it’s important to remember that even a below average hurricane season can produce an infamous storm such as Hurricane Alicia in 1983 and Hurricane Andrew in 1992.