The November 29 forecast from the Climate Prediction Center of the US National Weather Service (NWS) shows a reduced chance of La Nina, reinforcing previous forecasts that La Nina will be weaker and shorter.
For those unfamiliar with La Nina, the key is the ENSO cycle.
According to the NWS, the El Nino-Southern Oscillation (ENSO) cycle is a recurring climate pattern associated with changes in water temperatures in the central and eastern tropical Pacific Ocean.
Surface water over parts of the Pacific Ocean tends to warm or cool over time. The NWS calls this warming and cooling pattern the ENSO cycle.
ENSO, as defined by the NWS, is when neither phase of the ENSO cycle (El Nino and La Nina) is dominant. During this phase, sea surface temperatures in the Pacific Ocean are near normal. ENSO-neutral conditions remained strong this summer and continued through late November.
La Nina, unlike El Nino, is a cold event. During this phase of the cycle, trade winds strengthen and direct warm water toward Asia, cooling the Pacific Ocean off the U.S. coast, according to the National Oceanic and Atmospheric Administration (NOAA). When this happens and La Nina prevails during the winter, temperatures are typically warmer than normal in the south and colder than normal in the north.
While a strong La Nina can bring some significant weather impacts, forecasts continue to show the development of a weak and short-lived La Nina.
The chances of La Nina have decreased slightly compared to a few months ago. In September, La Nina was initially forecast to have a 66% chance of forming before the end of November; that number dropped to 60% in October.
Currently, the Climate Prediction Center is giving a 57% chance of La Nina appearing sometime before the end of December.
If and when La Nina materializes, it is expected to last only from January to March 2025. This “weak” and “short-lived” event is “unlikely to cause normal weather impacts,” according to the Climate Prediction Center report.
During a typical La Nina, this weather event can influence the trajectory of storms/depressions, leading to a more northerly track during the winter months.
La Nina winters are typically colder. The El Nino-affected winter of 2023-24 is expected to be one of the warmest, snowiest winters on record across the United States.
With a weak La Nina forecast, the phenomenon may not demonstrate the strength it usually has.
Meanwhile, according to the Vietnam National Center for Hydro-Meteorological Forecasting, the current standard error of sea surface temperature in the equatorial central Pacific region is -0.3 degrees Celsius lower than the long-term average in the first week of November 2024.
According to the latest forecasts, the probability of La Nina appearing in the last months of 2024 and early 2025 is significantly lower than previous forecasts.
In the next 3 months, La Nina is forecasted to have a 50-55% chance of appearing, although the average sea surface temperature for the 3 months is still lower than the average of many years, but it is unlikely to exceed the threshold of -0.5 degrees Celsius (the threshold to determine La Nina).
ENSO is likely to be neutral with a probability of 55-70% from around March to May 2025.
