La Niña January 2023 Update

La Nina is weakening this summer, and as we move forward to the middle of 2023 ENSO is expected to return to neutral. Model forecasts have lower accuracy this time of year, and typically accuracy improves after austral autumn (boreal spring) - the so called "autumn predictability barrier." In Jan 2022, many models predicted a return to El Nino later in 2022 - we know this didn't happen and in fact another La Nina eventuated.

So can we believe the forecast this time around? Will a fourth La Nina develop, despite tentative signals for an emerging El Nino later in 2023? Well, since the era of modern instrumentation, 4 consecutive La Nina events have never been recorded. This alone makes another La Nina return later this year statistically very unlikely.

Let's compare the current forecast with that of last year. The two images below show the Bureau of Meteorology ACCESS model forecast for Jan 2022 (left) and Jan 2023 (right). The solid black line indicates the mean, or average, forecast; the thin black lines depicts an array of ensemble members. These ensemble members define an envelope of possible model outcomes, and when there is a large spread in outcomes, as in Jan 2022, it corresponds to a large amount of uncertainty associated with the forecast. Skip forward to Jan 2023, and the right side image below is significantly different to Jan 2022, we note the ensemble forecasts cluster together and all show a similar evolution over time, suggesting less uncertainty compared to Jan 2022 (lower model skill notwithstanding). The current forecast shows La Nina conditions ending in the next month or two, then ENSO returning to neutral, before a possible El Nino episode later this year.

All of these factors means there is good confidence that La Nina will break down this summer and return to neutral in Autumn. Later this year, during the winter and spring months, it’s a toss-up between El Nino and neutral ENSO conditions, with models becoming more accurate about which scenario will play out once we get past March/April (and the "autumn predictability barrier" is behind us).