The anomaly at or below -0.5 persisted for 10 out of 12 overlapping periods in the 2020-2021 measuring season. For the first two periods of the 2021-2022 measuring season the anomaly continues in the negative at sum -0.9. The deepest anomaly in the last season was -1.3 in the October-November-December period, which is considered neither weak nor strong, but middling.
The trend toward lower ONI values since 1951 is consistent with wetter conditions in the Upper Midwest of the US, and greater incidence of tropical storms in the Atlantic from the 1980s. There is no need to adduce "global warming":
the historical tropical storm count record does not provide compelling evidence for a greenhouse warming induced long-term increase.
