La Niña strengthened in the last month, with below-average sea surface temperatures (SSTs) evident across most of the equatorial Pacific [Fig. 1]. In the last week, all of the Niño index values were between -0.7°C and -1.0°C, with the coolest anomalies in the Niño-3.4 region [Fig. 2]. Below-average subsurface temperatures (averaged from 180-100°W) were roughly the same amplitude at this time last month [Fig. 3], and reflected the prevalence of below-average temperatures in the eastern Pacific Ocean [Fig. 4]. Low-level easterly and upper-level westerly wind anomalies were again observed over parts of the equatorial Pacific, although weaker than last month. Tropical convection was suppressed near and west of the Date Line and was slightly enhanced over Indonesia [Fig. 5]. The Southern Oscillation Index and Equatorial Southern Oscillation Index remained positive. Overall, the coupled ocean-atmosphere system was consistent with La Niña.

The IRI/CPC plume average of forecasts for the Niño-3.4 SST index favors La Niña to continue through January-March 2022 season [Fig. 6]. The forecaster consensus anticipates La Niña to persist longer, potentially returning to ENSO-neutral during April-June 2022. The Niño-3.4 index has a 66% chance of reaching a value less than -1.0°C during November 2021 - January 2022, but only a 14% chance of being below -1.5°C. Thus, at its peak, a moderate-strength La Niña is favored. In summary, La Niña is likely to continue through the Northern Hemisphere winter 2021-22 (~90% chance) and into spring 2022 (~50% chance during March-May; 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. Nov. 18th).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA's National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Additional perspectives and analysis are also available in an ENSO blog. A probabilistic strength forecast is available here. The next ENSO Diagnostics Discussion is scheduled for 9 December 2021.

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