What will it take to have a below-average season?

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AlphaToOmega
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What will it take to have a below-average season?

#1 Postby AlphaToOmega » Sun May 08, 2022 9:46 am

Note: by "below-average", I mean a season with less than 73 ACE (73 is 75% the 1951-2020 ACE median).

Ever since 2016, we have seen above-average seasons (even in years with unfavorable Atlantic patterns). It makes sense why 2017 and 2020 were above average: the favorable Atlantic pattern combined with the -ENSO. Similar logic can explain why 2016 and 2021 were above-average. 2019 had a +ENSO, but it had a strong +AMM, which can explain its above-average activity.

However, 2018 is an oddball; during ASO, 2018 had a -AMM, Atlantic Nino, +PDO, and +ENSO; one would expect 2018 to be a below-average season, but it had 132 ACE. Granted, some of that could be due to better detection, but that alone cannot explain why 2018 was above-average; better detection cannot explain why 2018 was 59 ACE above the below-average threshold. Are we so entrenched in this +AMO that below-average seasons are becoming harder to achieve?

2022 is not expected to be a below-average season. In fact, based on my analogs for 2022 (1998, 2001, 2005, 2010, 2011, and 2020), 2022 has a 2.6% chance of being below-average. However, 2023 has a decent chance of being an El Niño year, which could make things interesting. Could a potential +ENSO be strong enough in 2023 to make it our first below-average season since 2015?
Last edited by AlphaToOmega on Sun May 08, 2022 11:36 am, edited 1 time in total.
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Re: What will it take to have a below-average season?

#2 Postby Category5Kaiju » Sun May 08, 2022 9:55 am

Of all the potential causes for a below-average season, the most reliable predictor is an El Nino. However, just because there is one does not mean we're 100% guaranteed to have a below average year. 1969, 2004, and 2018 are prime examples of this; those were extremely rare cases involving a Modoki El Nino allowing the Atlantic to have an above average season.

Or we could have a 2013 redux again, but the chances of that happening (let's face it)...is extremely low. That season was an oddball that should not be used as a baseline comparison for any given season due to how much of an outlier it was.

Also, do keep in mind that it's really hard to predict ENSO state this far out in time. 2023 may be expected to be +ENSO, but that does not mean it has to (for instance, what if it ends up as a cool neutral, much like 2001 did? You may never know).
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Re: What will it take to have a below-average season?

#3 Postby Yellow Evan » Sun May 08, 2022 12:10 pm

Africa shutting up is the answer here aside from the obvious +ENSO season.
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Re: What will it take to have a below-average season?

#4 Postby NotSparta » Sun May 08, 2022 12:28 pm

Yellow Evan wrote:Africa shutting up is the answer here aside from the obvious +ENSO season.


Well I think there'll be at least a handful of below average seasons before that
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Re: What will it take to have a below-average season?

#5 Postby al78 » Thu May 12, 2022 9:37 am

2018 was an oddball year where things flipped at the end of August from unfavourable to favourable. August was a quiet month but things took off in September. In addition, the sub-tropical Atlantic was much warmer than normal and storms steered into the sub-tropics (e.g. Florence) could tap into that. There was a lot of activitiy in the sub-tropics that year.

You can look at 2013 to see what it takes to have a below-average season. I'm not clear what killed that season given that standard climate pre-season parameters suggested at least an average season. Lots of dry air and subsidence over the tropical Atlantic is effective at killing hurricane activity.
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