Category5Kaiju wrote:WalterWhite wrote:Category5Kaiju wrote:It is indeed tempting to compare 2013 with 2022. However, I think the seasons have way more differences than similarities. For example, 2022 still featured major hurricanes (especially Cat 4 hurricanes; 2013 did not). 2022 was a true La Nina year (albeit third year La Nina), while 2013 was a cool neutral following a warm neutral year. There are some speculations that Hunga Tonga somehow messed up the atmospheric conditions early in 2022, which had downstream effects on the Atlantic hurricane season; 2013 did not feature such a kind of volcanic eruption.
With that being said, they do have some key similarities, the most striking of which is that the subtropics were exceptionally warm compared to the deep tropics and both years were also -ENSO years. I think the main reason why both seasons struggled with activity is that the subtropics were super warm and distorted stability. Phil Klotzbach did acknowledge after the 2022 season that in future indicator forecasts, he was interested to see how mid-level dry air and wavebreaking could be incorporated to better predict seasonal activity as it was clear from last year that wind shear isn't really the main killer of TCs; mid-level dry air is (which makes sense considering the Atlantic has had El Nino years in the past that featured destructive major hurricanes, something that even the -ENSO, basin-warm 2013 failed to achieve
).
Dry air affected 2020. It affected 2021. Both of those years were definitely above-average, and 2020 was hyperactive. There must be something more to this.
From 2016 to 2021, every season had above-average ACE and had an above-average number of storms---regardless of ENSO (2018 and 2019 were +ENSO years) or Atlantic SST patterns (2018 definitely did not have the most favorable Atlantic pattern). They all had over 130 ACE and over 15 storms; this seemed like the floor for 2022. The fact that 2022 was less active than any season from 2016 to 2021 (despite the more favorable SST patterns) indicates another factor at work. If not dry air, then what?
Well, mid-level dry air and Sahara Dust dry air are not exactly the same (the former is much more detrimental to TCs). Every year does feature some sort of dry air issue, hence why the Atlantic isn't as active as the WPAC or EPAC typically. Yes 2020 and 2021 had dry air issues, but such did not last until late August/early September and were not as severe as 2022. Last year uniquely featured mid-level dry air issues that suppressed TCs (especially in August and early September) because the subtropics were much warmer than the deep tropics, and there also seemed to be an associated phenomenon called "wave-breaking" where a PV streamer dipped down from the extratropics and invaded the subtropics and tropics, causing dry air from continental Europe to be continuously sent over the Atlantic. Now as to why this all happened in the first place? That remains to be analyzed by scientists, but there's definitely suspicion that the third year La Nina had something to do with it.
I also wonder if 2022 is like 2013 in the sense that it can basically be ignored when making season predictions. Both 2022 and 2013 dramatically underperformed prior years with similar background states. I wonder if 2022's major underperformance was so anomalous that it makes sense to ignore the season when making future predictions.
Think about it like this: every season from 2016 to 2021, regardless of ENSO, was above-average, at the time indicating that, under the current state of Atlantic conditions, above-average activity is virtually guaranteed. Then 2022 comes (a La Nina year, which is FAVORABLE for activity) and breaks the trend.
It being a third-year La Nina definitely might have contributed to the wave-breaking, and thus lower ACE, but such cannot fully explain why 2022 broke the streak of above-average activity because 2018 and 2019 were +ENSO years, which are usually less favorable for activity in the Atlantic than -ENSO years, regardless of whether the -ENSO event was 1st year, 2nd year, or 3rd year.