In December 2021, below-average sea surface temperatures (SSTs) across the central and eastern equatorial Pacific Ocean were consistent with a mature La Niña [Fig. 1]. With the exception of the westernmost Niño-4 region, which warmed to -0.4°C at the end of the December, the other Niño indices were between -0.9°C and -1.4°C during the last week [Fig. 2]. Below-average subsurface temperatures weakened east of the Date Line [Fig. 3], reflecting the slow eastward movement of positive temperature anomalies, at depth, from the western into the central Pacific Ocean [Fig. 4]. However, below-average subsurface temperatures still dominated the eastern Pacific from ~200m to the surface. Low-level easterly wind anomalies and upper-level westerly wind anomalies prevailed over the east-central and eastern Pacific Ocean. Enhanced convection persisted near Indonesia and the western Pacific, while suppressed convection remained over the Date Line [Fig. 5]. Overall, the coupled ocean-atmosphere system reflected a mature La Niña.
The IRI/CPC plume average for the Niño-3.4 SST index continues to forecast a transition to ENSO-neutral during the Northern Hemisphere spring [Fig. 6]. The forecaster consensus this month favors the continuation of La Niña through March-May 2022, with a transition to ENSO-neutral occurring in April-June 2022 (51% chance). ENSO-neutral is then expected to persist through the Northern Hemisphere summer, though chances do not exceed 57% (for May-July 2022), which is consistent with the generally lower confidence forecasts made through the spring. In summary, La Niña is likely to continue into the Northern Hemisphere spring (67% chance during March-May 2022) and then transition to ENSO-neutral (51% chance during April-June; click CPC/IRI consensus forecast for the chances in each 3-month period).
La Niña is anticipated to affect temperature and precipitation across the United States during the upcoming months (the 3-month seasonal temperature and precipitation outlooks will be updated on Thurs. Jan. 20th).