Oceanic La Nina ends by FEB 2023; La Nina Climate Lingers

Executive summary: La Nina is moderate-to-strong enjoying a 3^rd peak in intensity of the 2020-22 cold ENSO regime. However, dynamic and statistical ENSO phase forecast models are agreeable to La Nina ending in early 2023 coinciding with demise of negative Indian Ocean dipole (-IOD). However, the La Nina climate is unusually strong and could linger to the mid-point of 2023. El Nino remains a possibility for later 2023.

Fig. 1: Analog ENSO phase forecast comparing (oceanic) Nino34 and (atmospheric) multi-variate ENSO index.

Discussion: The 2020-22 La Nina climate will enter a 4^th year (2023) matching only 1973-76 and 1998-2001 in duration according to historical multivariate ENSO index (MEI). The MEI is a measure of the atmospheric climate in response to the equatorial Pacific environment which is dominated by the ENSO regime. Interestingly, despite the lengthy and increasingly robust La Nina climate, the oceanic (Nino34 SSTA) La Nina has a choppy character and is generally weaker than the MEI signature (Fig. 1). There are 5 reasonable analogs for the Nino34 regime including 1954-57, 1973-76, 1983-86, 1988-91 and 1998-01. Using the analogs to project the historical ENSO precedent for 2022 the oceanic La Nina should weaken early in the year while the La Nina climate ends mid-year. A weak El Nino may initiate during the last third of 2023. Dynamic models (using Nino34 SSTA) are all in agreement on dissipation of La Nina in early 2023 with neutral phase to follow by March (Fig. 2).

Fig. 2: Australia Bureau of Meteorology collection of dynamic models ENSO phase forecast for March 2023.

In October 2022, the global SSTA analysis from IRI/LDEO (Fig. 3) indicated the tropical environment of the Pacific Ocean was dominated by La Nina and a cross-equatorial flow from south-to-north hemisphere causing cool SSTA in the South Pacific tropics while just north of the equator SSTA was somewhat warmer. In the Indian Ocean cool SSTA dominated the western tropics while warm SSTA persisted north and northwest of Australia characteristic of negative phase of the Indian Ocean dipole (-IOD). The -IOD pattern is forecast to fade fast by early 2023 which should lower West Pacific tropical convection. Fading rising air associated with the tropical West Pacific convection should ease the trade winds sustaining La Nina across the eastern equatorial Pacific leading to weakening. There is likelihood of a significant eastward surging Madden Julian oscillation (MJO) coupled with an oceanic Kelvin Wave in January which should accelerate the La Nina fade indicated by dynamic and statistical models. An eastward shifting MJO coupled with a Kelvin Wave would be an eastward migration of subsurface warm water present now near and west of the Dateline (Fig. 4).

Fig. 3: IRI/LDEO analysis of global SSTA during October 2022 with annotated tropical SSTA regimes.

Fig. 4: Subsurface equatorial Pacific Ocean temperature anomalies.

Climate implications for DEC/JAN/FEB 2022-23 based on the ENSO projection include a dry climate across the Southern U.S. and Mexico and Argentina to Southeast Brazil plus a large portion of the Middle East. A wet climate is likely across the Interior Northwest U.S. and northern South America plus Southeast Africa and much of Australia. Dryness persists on much of the Asia East Coast. Temperature regimes include a hot summer in Argentina while Australia is generally cooler than normal. All of the subtropical latitudes of the northern hemisphere are warmer than normal. The cold winter candidates are Alaska/Western Canada and Central Russia.