La Niña strengthened during October, as indicated by well below-average sea surface temperatures (SSTs) extending from the Date Line to the eastern Pacific Ocean [Fig. 1]. The SST indices in the two westernmost Niño regions, Niño-4 and Niño-3.4 cooled further from last month, and the Niño-3.4 index was -1.5°C in the past week [Fig. 2]. The equatorial subsurface temperature anomalies (averaged from 180°-100°W) also became colder [Fig. 3], and continue to reflect below-average temperatures from the surface to 200m depth in the eastern Pacific Ocean [Fig. 4]. The atmospheric circulation anomalies over the tropical Pacific Ocean remained consistent with La Niña. Low-level wind anomalies were easterly across most of the tropical Pacific and strengthened during October. Upper-level westerly wind anomalies expanded over most of the tropical Pacific. Tropical convection continued to be suppressed from the western Pacific to the Date Line, and enhanced convection remained over Indonesia [Fig. 5]. Also, both the Southern Oscillation and Equatorial Southern Oscillation indices were positive. Overall, the coupled ocean-atmosphere system indicates the continuation of La Niña.
A majority of the models in the IRI/CPC plume predict La Niña (Niño-3.4 index less than -0.5°C) to persist through the Northern Hemisphere winter 2020-21 and to weaken during the spring [Fig. 6]. The latest forecasts from several models suggest the possibility of a strong La Niña (Niño-3.4 index values at -1.5°C) during the peak November-January season. The forecaster consensus supports that view in light of significant atmosphere-ocean coupling already in place. In summary, La Niña is likely to continue through the Northern Hemisphere winter 2020-21 (~95% chance for January-March) and spring 2021 (~65% chance for March-May; click CPC/IRI consensus forecast for the chances in each 3-month period).
La Niña is anticipated to affect climate across the United States during the upcoming months. The 3-month seasonal temperature and precipitation outlooks will be updated on Thurs. November 19th.