As Ben says, the only times on record in April (i.e. back to 1982) that Niño 1+2 was higher than now were in 1998 and 1983, but those were both AFTER a fall/winter with El Niño. In their respective Aprils the year before, which is comparable to April of 2023, the SSTs were much cooler.
Looking back all of the way to 1870, here's a link to monthly SST anomalies in Nino 1+2:
https://psl.noaa.gov/gcos_wgsp/Timeseri ... .anom.data
Looking at April, the warmest April monthlies all of the way back to 1870 in 1+2 by far are the aforementioned 1998 and 1983, which were as previously mentioned after rather than before their respective El Niño peaks. All other Aprils were over a degree cooler!
I then focused on April anomalies in Nino 1+2 just prior to the El Niños that reached +2.0+ in Nino 3.4 for 3 month averaged periods: 2015, 1997, 1982, 1972, 1965, 1888, and 1877.
- 2015: +0.6
- 1997: +1.0
- 1982: -0.5
- 1972: +1.1
- 1965: +1.7 (warmest of any pre-Nino April back to 1870)
- 1888: +0.9
- 1877: +0.0
The first week of April of 2023 is +2.7. It is as we know by far the most unstable Nino region from week to week. So, it could easily fall back sharply during the next few weeks. But if it doesn't fall back much, we'd end up with by far the warmest pre-El Nino April in Nino 1+2 for all El Niños back to at least 1870! We'd be so far into uncharted territory.
really odd that that index has 2018-19 PDO as cold.
