La Niña strengthened in the last month, with below-average sea surface temperatures (SSTs) evident across most of the equatorial Pacific, 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 Below-average subsurface temperatures (averaged from 180-100°W) were roughly the same amplitude at this time last month and reflected the prevalence of below-average temperatures in the eastern Pacific Ocean. 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 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. 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. El Niño and La Niña are opposite phases of what is known as the El Niño-Southern Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific (approximately between the International Date Line and 120 degrees West). La Niña episodes typically last nine to 12 months, but some prolonged events may last for years. We had a La Niña last winter as well. This Winter it is expected to be a moderate La Niña. El Niño and La Niña events occur on average every two to seven years. Typically, El Niño occurs more frequently than La Niña. La Niña events represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific. Global climate La Niña impacts tend to be opposite those of El Niño impacts. In the tropics, ocean temperature variations in La Niña also tend to be opposite those of El Niño. Keep in mind just because one area is showing above average temperatures or below average temperatures does NOT mean that it will be really cold or really warm the entire winter or that it means no snow if an area is expected to have below average precipitation.
Comments